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Sweeteners as food additives in the XXI century: A review of what is known, and what is to come
Accepted Manuscript Sweeteners as food additives in the XXI century: A review of what is known, and what is to come Márcio Carocho, Patricia Morales, Isabel C.F.R. Ferreira PII:
S0278-6915(17)30364-2
DOI:
10.1016/j.fct.2017.06.046
Reference:
FCT 9153
To appear in:
Food and Chemical Toxicology
Received Date: 23 May 2017 Revised Date:
26 June 2017
Accepted Date: 28 June 2017
Please cite this article as: Carocho, Má., Morales, P., Ferreira, I.C.F.R., Sweeteners as food additives in the XXI century: A review of what is known, and what is to come, Food and Chemical Toxicology (2017), doi: 10.1016/j.fct.2017.06.046. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Sweeteners as food additives in the XXI century: A review of what is known, and what is to come Márcio Carochoa, Patricia Moralesb*, Isabel C.F.R. Ferreiraa* Mountain Research Centre, (CIMO), ESA, Polytechnic Institute of Bragança, Campus
de Santa Apolónia, 5300-253, Bragança, Portugal b
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Department of Nutrition and Bromatology II, Faculty of Pharmacy, Complutense
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University of Madrid, Plaza Ramón y Cajal, s/n, 28040, Madrid, Spain
* Corresponding authors: Patricia Morales (email: [email protected];
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Telephone: +34913941808, FAX: +34913941799), Isabel C.F.R. Ferreira (email:
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[email protected]; Telephone: +351-273-303219; fax +351-273-325405)
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1. Introduction Mankind experiences the world through its five primary senses, and interprets the
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inputs with reason and emotion. This fragile human condition makes humans tend to prefer
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some stimuli, and hate other types of negative sensations (Mooradian et al., 2017). With
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regard to taste, it is widely known that children prefer sweet taste over the other basic
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flavors, and although this can change with age, sweet taste is still one of the most desired
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flavors for mankind, preferred over sour and bitterness (Kim et al., 2017). Research deems
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this preference as innate and linked it to sensations of pleasure and happiness. Moreover,
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other studies have proven that sugar craving could be genetic, making some individuals
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struggle with adverse effects of overconsumption of sweet food (Drexler and Souček, 2016;
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Padulo et al., 2017).
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In a profit driven economy, the food industry finds new ways to lure consumers to
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consume their products, paying little attention to the potential health effects of the
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cumulative consumption of various food products throughout the day. Thus, especial
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attention should be given to children and toddlers, for they are unaware of the
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consequences (Hert et al., 2014). For many years, the consumption of excessive sugar is
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known to have adverse effects in humans, and thus, to reduce its intake, sweeteners
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appeared back in the 1800’s. Since their inception, sweeteners have come a long way, and
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while they were once regarded as one of the most important achievements for the food
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industry, many controversies, conflicting regulations and laws have deemed them to
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untrusted molecules that are added to food to make it sweeter. Today, metabolic disorders
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are increasing, obesity is increasing, and so are diabetes and other diseases that are directly
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related to sugar consumption, in fact, the WHO studies have considered metabolic disorders
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as being of “epidemic proportions” in industrialized countries (Pradhan, 2007; Rani et al.,
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2016). With the increasing prevalence of diseases related to sugar consumption, sweeteners
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are now widespread in foodstuffs, and are highly researched for their impact on sweetening
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potentials, on health, on the economy and in social studies (Mooradian et al., 2017). In this article, the authors review the sweeteners state of the art (classes, behaviors,
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applications, benefits, disadvantages, scandals, and corporative tactics), and postulate future
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trends in food sweetening.
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2. General considerations
The most important aspect of sweeteners is undoubtedly their sweetness; it is
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measured in relation to sucrose, which is the reference sugar. Thus, a solution of 30 g L-1 at
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20 ºC has a sweetening power of 1, with the threshold of the minimum concentration to
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detect sugar being 1-4 mM. For the sweet flavor intensity to be perceived, the substance
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must first be dissolved in saliva and come into contact with the receptors that are present on
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the tongue. Other parameters influence the sweet flavor, namely the sugar structure (in
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which the intensity decreases as the number of monosaccharides increase), temperature of
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perception, pH and the presence of other molecules that can influence receptors.
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Taking sucrose as a reference (its reference value can be considered 1), it has a higher
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sweetening power when compared to other simple sugars, for instance, galactose (0.3),
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while others show higher values, namely fructose (1.7). Furthermore, there are other highly
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complex sweeteners that have thousands of times the sweetening power of sucrose,
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neotame (13,000 times sweeter) or even advantame, which is 37,000 times stronger than
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sucrose (Table 1) (Ordoñez et al., 1998).
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Table 1. Difference of sweetness among different molecules, calculated based on the
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assumption that sucrose is equivalent to 1 unit of sweetness. Data extracted from Mitchell,
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2006; Otabe, 2011c; Varzakas et al., 2012. Sweetening power
Advantame
37000
Neotame
7000-13000
Neohesperidin
1500-2000
Sucralose
400-800
Saccharin
240-300
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Acesulfame-K
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Cyclamate
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Fructose
1.1-1.5
Sucrose
1
Xylitol
1
Dextrose
0.9
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Sweetener
Maltitol
0.75
Glucose
0.75
Erythritol
0.7
Mannitol
0.6
Sorbitol
0.6
Isomaltose
0.55
Maltose
0.4
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Lactitol
0.35
Galactose
0.3
Raffinose
0.2
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Biologically, the perception of sweetness happens through the receptors on the taste buds,
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based on a donor/acceptor proton system, establishing an AH/B/X system between the food
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and the receptors of the taste buds. A and B are electronegative atoms, like oxygen or
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nitrogen, H represents hydrogen, which is connected to an atom (A) through a covalent
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bond. X represent hydrophobic groups that are attracted by the taste buds in order for the
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AH/B/X to become tridimensional. The receptors of the taste buds are coupled to G
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proteins (T1R2 and T1R3), forming part of the C class of proteins (GPCR), which are
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structurally similar to the glutamate metabotropic receptors. The bond between sweet
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molecules with the AH/B/X structure with these receptors happens through hydrophobic
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hydrogen bonds. This bond changes the configuration of the “taste sensible” receptor,
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altering the permeability of the ionic environment, aiding the entrance of Na+
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(Shallenberger and Acree, 1971). For a compound to display a sweet taste, the molecular
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distance between A and B must be at least 0.25 to 0.40 nm. The sensation of sweetness also
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depends on the configuration of the molecule, which in sugars comes from the dextrorotary
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conformations, but not from the inverse, levorotary. For this reason, some sugars, like
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cellobiose are insipid, but others are sweet (D-glucose), while L-glucose is slightly salty.
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The three-dimensional structure of D-glucose binds to the receptor with the hydroxyl group
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of C4 (AH function) and the oxygen in C3 (B function), together with the hydroxyl group
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of C6, they bind to the receptor through hydrogen bonds (Crammer and Ikan, 1979;
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Lindemann, 2001). The activation of such receptors by sweet substances releases adenosine
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triphosphate (ATP) that consequently activates neurons that transmit this input to the brain.
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Apart from depending on physical and chemical properties of the substances, sweet flavor
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is also determined by differences in humans, namely age, genetics, race and ethnicity
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(Nelson et al., 2001; Ohtsu et al., 2014; Smutzer et al., 2014; Weerasinghe and DuBois,
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2006).
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3. Classification, properties and sweeteners role in food
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Sweeteners (as legal food additives and non-additives) can be classified by intrinsic
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properties or origin. Some of the most common classifications are in terms of their nutritive
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value, sweetening power and their provenance. Thus, they can be divided in nutritive vs.
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intensive sweeteners (Figure 1A and 1B), but also between synthetic and natural origin
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(Figure 2). While the former is a classification used by governing bodies like the European
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Food Safety Authority of the European Union (EFSA) the division in natural and synthetic
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food additives is not used by these organizations, and is based solely on the origin of the
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sweetener.
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A
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Figure 1. A – Examples of nutritive sweeteners. B – Examples of intensive sweeteners.
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Figure 2. Examples of synthetic and natural sweeteners.
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In the nutritive sweeteners group (Figure 1A) are the simple sugars but also high
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fructose corn syrup, isomaltulose, trehalose, which, under the Regulation (EU) No
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1333/2008 cannot be considered food additives, but ingredients. Furthermore, polyols
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(which are considerd as food additives) are also included in this classification; examples of
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polyls are erythritol, isomaltitol, lactitol, maltitol, sorbitol, mannitol, and xylitol. On the
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other hand, the intensive sweeteners, all of them considered as food additives (Figure 1B),
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have negligible caloric contribution and high sweetening capacity, being used in low
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quantities in food. Generally, they are not cariogenic and do not trigger glycemic response,
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thus being extensively used in hypocaloric diets, for diabetes patients and other specific
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cases where caloric intake must be controlled (Baines and Seal, 2012; Varzakas et al.,
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2012).
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The other classification, presented in Figure 2. divides sweeteners by their nature or origin,
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which can be either synthetic or natural. Sucrose, a disaccharide, the most used table sugar, known commonly as sugar and
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the most used sweetening agent in the world. It is composed of a molecule of glucose in
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which the aldehyde carbon is joined to the ketone one of fructose, forming a b(1,2) bond,
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preventing any reducing properties and forming an adequate structure to bind to the taste
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bud receptors, conferring the traditional sweet taste. For some time now, the relation
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between the consumption of this sugar and dental decay has been established, given that it
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is the substrate for bacteria, like Streptococcus mutans and S. sanguis that use this
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disaccharide and convert it to pyruvic, acetic and lactic acid, which dissolve the tooth
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enamel, fostering bacterial colonization. Furthermore, the very fast absorbance of sucrose
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can make glycemic values spike, causing hormonal problems, thus the danger if its
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consumption by some diabetic patients (Valdés-Martínez, 2006). Other diseases and
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disorders are also related to sugar consumption, among them are cardiovascular diseases
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(coronary), type II diabetes, metabolic syndrome, hypertriglyceridemia, insulin resistance,
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cancer (breast, colon), obesity, childhood obesity, hypertension and kidney diseases
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(Bostick et al., 1994; Grundy, 1999; Johnson et al., 2007; Ludwig et al., 2001; Mente et al.,
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2009; Slattery et al., 1997; Stanhope et al., 2013; Touger-Decker and van Loveren, 2003;
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Yang et al., 2014).
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For these reasons, the role of sweeteners has been paramount in the dichotomy of
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food and health, and their impact on our daily life, longevity and quality thereof is
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staggering. Thus, the changes of food consumption have been drastic, with sweeteners
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chugging alongside the industrialization of food and food components, being their
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discovery a revolution in the food sector. This allowed the production of sweet food
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without caloric intake, changing the paradigm of how we eat, and of vital importance to
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people with hypocaloric diets and diabetics. For the latter, polyols, for instance, as like
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fructose, display a metabolization that is independent from insulin, given that they may
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enter the hepatic cells through the action of the enzyme fructocinase, which is independent
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from insulin, which also deems them safe for these patients. Furthermore, many sweeteners
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are not cariogenic, so they are not used as subtract for oral bacteria.
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Some of the most used sweeteners worldwide are aspartame (E951), cyclamates
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(E952), acesulfame K (E950), tagatose (considered “generally regarded as safe” (GRAS)
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by the Food and Drug Administration of the United States of America (FDA)), sucralose
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(E955) and more recently steviol glucosides (E960).
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3.1. Polyols: Classification and applications
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Polyols, polyhydric alcohols or polyalcohols, are food additives that result of the
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hydrogenation of reducing sugars, being the presence of an alcohol group in the place of the
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carbonyl group quite common in the aldose or ketose fractions of mono, di, oligo and
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polysaccharides. Polyols are stable at high temperature, pH changes and do not intervene in
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Maillard reactions. They can be found in nature, especially in fruit and vegetables, being
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partially responsible for their sweetness. Their industrial production started in the 20’s with
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hopes of solving health problems related to excessive sucrose consumption. Nearly 90
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years after, polyols are the most consumed group of sweeteners because of their lack of
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cariogenic properties, salivation induction, and no interference in insulin levels, being used
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in “light” foods (Nabors, 2001 (Chapter II); Varzakas et al., 2012). On the other hand, their
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consumption is not recommended for toddlers under 1 year of age, due to their laxative
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effects that can unleash severe diarrheas. Technologically, polyols are also important,
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namely for reduction of water activity, as humectants, inert to Maillard reactions,
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texturizing agents, sugar crystallization mediators, flavoring solubilizers, and so on. When
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being used for these purposes, they are labelled quantum satis (latin for “just far enough”
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meaning that there is no limit for its use, as long as the least amount for the specific
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outcome is used) (EU Regulation 1333/2008; EU Regulation 1129/2011). The most used
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polyols are sorbitol (E420), mannitol (E421), isomaltose (E953), maltitol (E965), lactitol
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(E966), xylitol (E967), erythritol (968). Less used, but also with relevance are arabitol and
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hydrogenated starch hydrolysates (HSH), although not allowed within the EU.
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Sorbitols (E420) and mannitols (E421) are isomeric polyols and have been use in
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food since the 40’s through glucose syrups, inverted sugars and other hydrolyzed starches.
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Their production is based on the catalytic hydrogenation of glucose with subsequent
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purification. The separation of the isomers is done by solubility difference, yielding a very
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hygroscopic sorbitol and a much less mannitol. Sorbitol is 50 to 60% sweeter than
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mannitol, making it preferably used as sweetener, while mannitol is employed as an anti-
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caking agent (Song and Vieille, 2009). Overall, these polyols are used in baked goods,
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sweets, bubble gum, surimi, sausages and drinks (Nabors, 2001 (Part II)). Although there is
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no evidence of sorbitol toxicity, in 2016, a study found that sorbitol can be genotoxic and
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induce metabolic reactions in offspring of female wistar albino rats fed sorbitol. A study
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found that patients with irritable bowel syndrome (IBS) have adverse gastrointestinal
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reactions to polyols, especially sorbitol and mannitol, being these reactions independent of
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the absorption patterns of each molecule. While sorbitol can be of concern for patients with
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IBS, it seems to be safe for healthy individuals, although there are reports of laxative
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effects when consumed in high doses. Some studies point out that this effect is related to
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the fructose:glucose:sorbitol ratio that is consumed, and not to sorbitol itself (Hoekstra et
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al., 1993; Yao et al., 2014). Mannitol, although less sweet than sorbitol is also used in food,
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given its high metabolization ratio, about 75%, being the other 25% absorbed before being
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excreted in urine. Because it is virtually inert, it does not react with active components of
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drugs and confers a cool sweet taste, apart from being used in the food industry, it is also
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widely used in the pharmaceutical area in dental hygiene products, drug filler and as a
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diuretic in intravenous fluids (Biesiekierski et al., 2011; Lee, 2015; Livesey, 2003;
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Mitchell, 2006;). B
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Figure 3. Chemical structure or sorbitol (A) and mannitol (B).
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Isomaltose, isomaltitol, or isomalt (E953) in a legal polyol in the EU and the USA,
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obtained through enzymatic transformation of sucrose (Cammenga and Zielasko, 1996). It
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is stable at high temperatures and has a very low hygroscopic value. Its sweetening power
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is in line with other polyols, about 45 to 60 % of sucrose, but a very low caloric
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contribution, of about 2 kcal g-1. This molecule is not absorbed by the small intestine, and is
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readily fermented in the colon through colonic bacteria (Caballero et al., 2016). Isomalt is
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used in bubble gums, gelatins, chocolate, coatings, baked goods and yogurts, among others
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(Grenby, 1996; JECFA, 2003).
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Figure 4. Chemical structure of isomaltose.
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Lactitol (E966) is a disaccharide that is obtained by hydrogenation of lactose. It was
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discovered around 1920 and since then has been used in many different foods. Given its
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limited sweetening power compared to the other polyols it is usually used in combination
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with intense sweeteners, like acesulfame K, aspartame and sucralose. The human body does
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not metabolize this polyol, therefore it has no caloric contribution (Mitchell, 2006). Still, it
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only has a sweetening power of 30 to 40 % of sucrose and a lower solubility that xylitol
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and sorbitol. Its taste, apart from being sweet gives a fresh aftertaste, and is therefore used
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to confer different kind of sweetness to food. Furthermore, it is also used to increase food
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volume, as a probiotic, while also not being cariogenic. Lactitol exists in four crystallized
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crystalline forms: anhydrous lactitol, lactitol monohydrate, lactitol dehydrate, and lactitol
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trihydrate, being the anhydrous the most stable form of this compound. The foods it is used
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in are chocolates, baked goods, bubble gums and ice creams (Aidoo et al., 2013; Grenby,
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1996; Halttunen et al., 2001; Mitchell, 2006).
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Figure 5. Chemical structure of lactitol.
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Maltitol (E965) is obtained by hydrolyzation, reduction and hydrogenation of starch,
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resulting in a sweetener with about 90% of sweetening capacity, no other residual flavors
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and very high stability (Maguire et al., 2000; Pratt et al., 2011). Of all the sugar alcohols, it
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is the one that most resembles the flavor of sugar. It is not cariogenic and safe for diabetics.
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In terms of solubility and hygroscopicity it is very similar to sucrose, thus being the
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preferred sugar to use in the production of chocolate in which the label says “no sugars
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added” (Joshi, 2016). It has a very slow digestion rate, being fermented in the colon. Apart
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from chocolates, it is also employed in lactic products, baked goods, muffins, bubble gum,
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jams, jelly and other sweets (Grenby, 1996; Mitchell, 2006;).
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Figure 6. Chemical structure of maltitol.
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Xylitol (E967), a five-carbon polyol, obtained by hydrogenation of xylose, was first
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synthesized in 1891 and has about 95% the sweetness of sucrose. Of all the polyols, it is the
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sweetest, contributing only 2.4 kcal g-1. This compound is obtained by extraction from
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birch and other woods, almond husks, corncobs, straw and paper production surplus. Apart
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from this, and although not viable for industrial production, xylitol is also found in many
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fruits and vegetables (Nabors, 2001 (Part II); Mitchell, 2006). It is known to increase
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salivation, thus increasing teeth cleansing and reducing the bacterial load in the mouth and
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therefore teeth decay. Xylitol is used in bubble gum, refreshments, baked goods, among
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others. It is estimated that this sweetener has a market of 670 million dollars worldwide,
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which has been increasing 6% per year, and is expected to continue growing until 2020.
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These figures, in line with what is happening transversally to all food additives, represent
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the increasing awareness of naturally derived food additives (Dasgupta et al., 2017;
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Mitchell, 2006; Peterson, 2013).
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Figure 7. Chemical structure of xylitol.
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Erythritol (E968), used legally both in the EU and the USA, appears naturally in some
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fruits (melon, pears and grapes), but also in vegetables, mushrooms, honey and seaweeds,
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but its primary method for industrial production is through yeasts (Boesten et al., 2015
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Tomaszewska et al., 2014). Being discovered in 1848, today it takes part in a multitude of
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products, like food coatings, baked goods, fermented milk, glazed goods, candy, and
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chocolate (Carocho et al., 2015). Its sweetening power is about 60 to 80% of that of sucrose
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and a very low caloric contribution, of just 0.3 kcal g-1, therefore being safe for diabetics.
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Furthermore, erythritol is easily absorbed through the intestine and has a very low
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metabolization, being almost completely excreted in urine (Arrigoni et al., 2005; Röper et
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al., 1993). Erythritol is considered as a safe additive after many specific tests regarding
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toxicity, carcinogenicity and reproductive hazards resulted negative, although in 2013,
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there was report of an 11-year-old child that had erythritol induced anaphylaxis (Shirao et
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al., 2013). This sweetener also displays antioxidant capacity and has protective endothelial
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properties (Boesten et al., 2015).
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Figure 8. Chemical structure of erythritol.
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Apart from these polyols, there are others, although these cannot be used in food inside the
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EU, namely arabitol, which is obtained by reduction of arabinose, and HSH, which is a
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mixture of polyols that can achieve about 90% of sweetening power. In the USA, these
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sweeteners are legal, and actually considered GRAS food additives. Arabitol has a very
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similar structure to sorbitol (6-carbon skeleton) and is used for its rheological properties,
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viscosity improvement, humidifying, crystallization and rehydration properties of the
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foodstuff it is used in (Carpentier et al., 2013; Modderman, 1993). HSH are a family of
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bulk nutritive sweeteners that comprehend hydrogenated glucose, maltitol and sorbitol
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syrups. They were first developed in the 60’s in Sweden and have been used in foodstuffs
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since then. They are produced by hydrolysis and hydrogenation of corn, wheat or potato
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starch, and a caloric contribution of 3 calories per gram, not causing tooth decay.
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Furthermore, HSH can be used as viscosity and bodying agents, humectants, crystallization
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modifiers and rehydration aids. (Larry and Greenly, 2003). On Table 2 some of the most
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important polyols used in food are displayed, along with their chemical structure and
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caloric contribution per gram.
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Figure 9. Chemical structure of arabinose (A), the precursor of arabitol (B).
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Figure 10. Chemical structure of hydrogenated starch hydrolysates.
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Table 2. Most used polyols and caloric contribution in kcal g-1. Data extracted from
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Varzakas et al., 2012.
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Caloric Name contribution
Hydrogenated starch hydrolysates
2.8
Maltitol - E 965
2.7
Sorbitol - E 420
2.5
Xylitol - E 967
2.5
Isomaltose - E 953
2.1
Lactitol - E 966
2
Mannitol - E 421
1.5
Erythritol - E 968
0.2
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4. Intensive sweeteners
Intensive sweeteners are those that present a high sweetening power, higher than
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sucrose, thus only being necessary in very low doses to obtain intense sweetness. Their
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caloric contribution is also very low or even virtually zero, they also present no danger in
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terms of cariogenicity or insulin reaction and have no other function in food apart from
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sweetening.
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4.1. Synthetic intensive sweeteners
Among all the intense sweeteners used in the industry, the most notable ones are
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acesulfame K (E950), aspartame (E951), cyclamates (E952), saccharin (E954), sucralose
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(E955) and neotame (E961), which are detailed in Table 3. Recent research has showed the
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impact of neural mechanisms involved in the sweet taste, and related that, like all things
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sweet, sweeteners modulate neural systems, perpetuating their intake, although in different
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manners. Both caloric and non-caloric sweeteners act on the reward mechanisms, and in
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situations of caloric deficit, caloric sweeteners excerpt stronger craving. Thus, non-caloric
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sweeteners potentially act with lower intensity in neuronal paths of reward, but is their
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contribution to health and industry innocuous? Probably not… Recent studies suggest that
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non-nutritive sweeteners can, surprisingly, be related to weight gain and type 2 diabetes
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risk through 3 potential mechanisms: a) interference with learned responses that contribute
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to control glucose and energy homeostasis; b) interference with the gut microbiota,
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inducing glucose intolerance; c) interaction with sweet-taste receptors that may trigger
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insulin secretion (Murray et al., 2016; Pepino, 2015).
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Acesulfame K (E950) corresponds to the potassium salt of acesulfame, and was
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discovered in 1967, although today, its industrial production has changed, being obtained
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through sulfamic acid and deketene which will eventually produce sulphur. Acesulfame K
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is one of the most used synthetic sweeteners due to the lack of residual flavors and a
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sweetening power of over 200 times the one of sucrose. It can be used in synergies with
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other sweeteners, namely aspartame, cyclamates and sucralose to further improve
314
sweetening and flavor. Unlike polyols, this compound suffers metabolization by the human
315
body, thus having an admissible daily intake (ADI) of 15 mg kg-1 of body weight. The ADI
316
is the maximum amount of a compound that can be ingested per kg of body weight per day,
317
considering all the sources of the compound. Many studies have described its
318
innocuousness, although other studies up until 2000 pointed some type of toxicity, but were
319
then disproved (Carocho et al., 2014; Shankar et al., 2013). Still, studies carried out by
320
Stohs and Miller (2014) claim that there is some type of hypersensitivity at a dose
321
dependent manner. Acesulfame K is used in baked goods, cereals, sweets, confectionary
322
products, marmalades, canned food and fruit, bubble gum and as tabletop sweeteners (for
323
coffee and others) (Nabors (Part I), 2001; Mitchell, 2006; O’Donnell and Kerasley, 2012).
324
A new problem related to acesulfame k and other synthetic sweeteners is their ubiquity in
325
the environment given the high amounts that are consumed by populations and excreted
326
into wastewaters. Thus, a considerable amount of research groups are trying to find new
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ways to inactivate this contaminant, for it is excreted unaltered due to the lack of
328
metabolization in the human body. In surface waters, its concentration can achieve 1 µg L-1,
329
which is higher than the concentration of the average contaminant. The major problem is
330
that the residue produced by its inactivation is more toxic than acesulfame k itself, which
331
consists of yet another challenge to the food/environmental industries with regard to
332
synthetic food additives (Yin et al., 2017). B
O O
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A
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S
O
O
333 334
K+
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Figure 11. Chemical structure of sulfamic acid (A) and acesulfame K (B).
335
Aspartame (E951), discovered in 1965 is obtained through the combination of amino acids,
337
namely L-phenylalanine, L-aspartic acid, and connected through methyl ester bonds. Given
338
is extremely low solubility in water and unstable pH it cannot be used in refreshments with
339
low pH like juices, and does not resist to prolonged heat and pasteurization procedures, thus
340
having very high stability, even higher then saccharin and acesulfame K. It has a pleasant
341
taste without sourness or metallic residue (usual in some types of sweeteners) and a
342
sweetening capacity of 180 to 200 times sucrose. It is however, considered a source of
343
phenylalanine thus not being advised for people with phenylketonuria (Shankar et al.,
344
2013). Furthermore, there are reports of toxicity and hepatocellular alteration in long-term
345
exposure to it (Abhilash et al., 2011). According to regulation of the EU No. 1169/2011, all
346
food that uses aspartame has to have a visible section containing “contains aspartame
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(source of phenylalanine)”. Its ADI is 40 mg kg-1 of body weight. Further recommendations
348
should be considered, given that the use of aspartame in food with a pH higher than 6 can
349
make it transform into diketopiperazine, a carcinogenic compound (Rycerz and Jaworska-
350
Adamu, 2013). Aspartame is used in refreshments, yogurts, lactic beverages, desserts,
351
baked goods and others (Mitchell, 2006; Nabors (Part I), 2001; O’Donnell and Kearsley,
352
2012). It has always been a target of intense studies regarding its safety, although being
353
widely regarded as safe, this sweetener has seen recent studies, (2010 and onwards)
354
pointing outs its nephrotoxicity, hepatotoxicity, damage to nerves, cancer, and even type 2
355
diabetes (which is strange given the non-nutritional nature), being all these diseases
356
reported in murine models (Ashok et al., 2013; Fagherazzi et al., 2013; Haliem and
357
Mohamed, 2011; Okasha, 2016 Saleh, 2014; Soffritti et al., 2010). Despite having evident
358
differences, the human body and metabolism shares some similarities with these models,
359
which perpetuates the mistrust of this molecule by the public. Inversely, a review published
360
in the Food and Chemical Toxicology Journal, authored by Kirkland and Gatehouse in
361
2015, deems aspartame safe, after reviewing all available data from various sources. The
362
authors state no toxicity in gene mutations, some evidence of chromosomal damage in
363
vitro, while bone marrow micronucleus, chromosomal aberration and comet assays found
364
no toxicity in somatic cells, supporting the claim by the EFSA of a non-genotoxic
365
compound. In 2014, an article signed by Suez et al. and published in Nature referred to
366
aspartame as inducing glucose intolerance by altering gut microbiota, requesting that a
367
reassessment of non-caloric artificial sweeteners be carried out. Concomitantly, PepsiCo
368
announced in 2015 that they would remove aspartame from their diet version of the famous
369
drink, bowing to consumer demand of an aspartame free drink. In 2016, after a crash in
370
sales, PepsiCo reintroduced aspartame in their beverage, claiming that some consumers
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found a difference in taste, making the company produce three types of beverage: the
372
original Pepsi, one with aspartame and one with a natural sweetener to meet all customer
373
demands. This small industrial maneuver further deepens the plot and casts more distrust
374
and fear in customers, which are left baffled without actually knowing if aspartame is safe
375
or not (CNBC, 2015, 2016;Paolini et al., 2016). A
SC
B
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C
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377
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371
Figure 12. Chemical structure of the amino acids L-phenylalanine (A), L-aspartic acid (B),
379
which are the building blocks of aspartame (C).
380
EP
378
Cyclamates (E952), discovered in 1937 at the University of Illinois, are a very good
382
example of the legislative discrepancies between the EU and USA. The European Union
383
has approved its use in food, while the FDA removed its GRAS status in 1969 and
384
completely banned it in 1970. It is now pending approval for re-admission. The base for
385
this ban is a study that relates the metabolization of cyclamates to cyclohexylamine (toxic
386
compound), and although a later study pointed out that this metabolization only takes place
387
in a small amount of the population, it has not been enough for the FDA to remove the ban.
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Its industrial production could be the reason for this intransigent maneuver, given that it is
389
obtained though the sulfonation of cyclohexylamine (Renwick and Nordmann, 2007).
390
China, Indonesia, Taiwan and Spain are the biggest producers of this sweetener, which,
391
along with saccharin are the least expensive to produce (Nabors (Part I), 2001). In the EU,
392
the ADI is set at 11 mg Kg-1 of body weight and is used in desserts, baked and processed
393
food, soft drinks, canned fruits, gelatins and as tabletop sweeteners (Carocho et al., 2014).
394
One of the drawbacks of cylamates is the slight sour taste, although its sweetening capacity
395
is set between 35 to 50 times stronger than sucrose. The long-lasting sweetness if put off by
396
a sour aftertaste, so it is almost always combined with saccharin (Martins et al., 2010;
397
Mitchell, 2006O’Donnel and Kearsley, 2012; Renwick et al., 2004; Roberts, 2016;
398
Takayama et al., 2000).
399
B
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A
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388
Figure 13. Chemical structures of the precursor cyclohexylamine (A) and sodium
401
cyclamate (cyclamate) (B).
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400
403
Saccharin (E954) was the first discovered intense sweetener, back in 1878. Today, more
404
than 100 years later, it is produced at an industrial scale, though a process called Maumee,
405
which derives from the company that developed the technique (Maumee Chemical
406
Company). In this process, phathalic anhydride is converted to anthranilic acid to then react
407
with nitrous oxide, nitrogen dioxide, chlorine and ammonia, forming saccharin Carocho et
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al., 2014 Mitchell, 2006. This compound is stable at low pH and resists high temperatures,
409
which makes it an ideal sweetener to be used in production steps of foods and for long
410
lasting goods. It has a sweet taste, but also a slight acid contamination so it is combined
411
with cyclamates and aspartame. It can have 300 times the potency of sucrose in terms of
412
sweetening, but has the lowest ADI of all non-caloric sweeteners, only 5 mg Kg-1 of body
413
weight. In terms of consumption, it has always been controversial, with Canada banning its
414
use in 1977 after animal testing showed toxicity. In that same year, the US considered
415
doing the same, but Congress placed a moratorium on this decision, having other studies
416
then ruled out the adverse effects. All these studies were based on the formation of tumors
417
in rats, namely in the bladder (Nabors (Part I), 2001). Thus, given the anatomical
418
differences between mouse and man, the danger for humans was ruled out. Today,
419
numerous studies have deemed saccharin safe and its consumption is, today, safe, fostering
420
the increase of its use all over the world (Shankar et al., 2013). As like acesulfame K,
421
saccharin is excreted through urine and is not metabolized in the body, although it can cross
422
the placenta of pregnant woman and can be transferred through breast milk, thus not being
423
recommended to pregnant women or breastfeeding ones. It is employed in fruit juices,
424
processed fruit, gelatins, marmalades, coverings, sauces, desserts, bubble gum and tabletop
425
sweetener (Swither et al., 2013; Takayama et al., 1998; Whysner & Williams, 1996).
SC
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426
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408
427
Neotame (E961) is a sweetener with a very similar structure to aspartame, in fact, they are
428
isomers, but neotame has a very high sweetening power, from 7000 to 13000 times stronger
429
than sucrose and less than 1.2 kJ g-1 Mayhew et al., 2003. It has a clean taste, with no
430
metallic or acid aftertaste. Like sucralose, it was only discovered in the 80’s and is obtained
431
by reductive alkylation of aspartame, which is converted into 3,3-dimethylbutyraldehyde.
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Given the lack of phenylalanine in its composition, it is safe for phenylketonuria patients,
433
but also safe for diabetics O’Donnell and Kearsley, 2012. It is used mainly in synergies
434
with other sweeteners (except acesulfame-k and saccharin) and for soft and lactic drinks,
435
sauces, yogurts, lemon tea, as tabletop and in bubble gum, but also as an enhancer of
436
natural flavors, namely acidic fruit flavors. It is stable under dry storage conditions, not
437
hygroscopic and appears a white crystalline odorless powder. In terms of metabolization,
438
half of the ingested neotame is not absorbed and excreted through the feces while the other
439
half in excreted in the urine as de-esterified neotame. It meets the five basic criteria for
440
commercial viability of a nonnutritive sweetener: taste, solubility, stability, safety and cost.
441
Regarding safety, neotame, as has been subject to a battery of tests, in which, even at doses
442
higher that its ADI, no toxicity was detected. No adverse findings were reported for
443
physical examinations, water consumption, clinical pathology evaluations, no reports of
444
morbidity, mortality, organ toxicity, macroscopic or microscopic postmortem findings in
445
murine models and other test animals (Mitchell, 2006; Nabors (Part I), 2001; Nofre and
446
Tinti, 2000; Zhu et al., 2016).
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Advantame (E969) is one of the newest sweeteners to be approved in the EU, in 2013. It is
449
obtained through chemical synthesis from aspartame and isovaniline. Contrary to neotame,
450
advantame is a source of phenylalanine, and even though it is derived from aspartame, it
451
has a very different structure. The sweetening power of this molecule is around 20,000
452
times the one of sucrose and it appears a white to yellow powder (Warrington et al., 2011).
453
It has a very sweet flavor with little intensity of bitter and sour. It has been successfully
454
used in coffee, iced tea, powdered beverage formulations, chewing gum, yogurt, and also as
455
a flavor enhancer (Otabe et al., 2011a). In terms of stability, it can withstand high
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temperatures and be used in low pH products.
In July 2013, EFSA experts defined
457
advantame as non-toxic or carcinogenic and there are no risks of its consumption as a food
458
additive. The ADI was established at 5 mg kg-1 of body weight per day. Model animal (rats,
459
dogs) and human trial data suggest that there are no issues with the use of advantame as a
460
food sweetener (EFSA, 2013; Otabe et al., 2011b; 2011c; 2011d; Ubukata et al., 2011).
RI PT
456
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A
461 462
AC C
463
EP
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B
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SC
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C
464
Figure 14. Chemical formulas of A – saccharine, B – neotame, and C – advantame.
M AN U
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Sucralose (E955) is another intense synthetic sweetener, obtained industrially by
468
substitution of the three hydroxyl groups in sucrose Roberts et al., 2008. This
469
transformation renders this molecule 750 times sweeter than the precursor, sucrose. Its ADI
470
is 5 mg kg-1 of body weight (as saccharin), although sucralose suffers metabolization in the
471
human body. This metabolization is related to migraines, intestinal unrest and inhibition of
472
colonic bacteria when consumed in high amounts. The principal applications of sucralose
473
are yogurts, ice cream, canned fruits, biscuits, caramels, soft drinks, lactic products, baked
474
goods, gelatins, marmalades, bubble gum, among others Mitchell, 2006; Nabors (Part I),
475
2001; O’Donnell and Kearsley. Despite some research pointing out the possible connection
476
of the consumption of sucralose with cancer at the beginning of the century, a review article
477
authored by Berry et al. (2016), stressed that there is no relation, even at higher dosages
478
that the previewed in the ADI. Furthermore, back in 2009, another review article that
479
thoroughly reviewed all the available studies at the time pointed out that there are no risks
480
in consuming this additive, and many studies in vivo, in vitro and with human trials point
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out the overall safety of sucralose Grotz and Munro, 2009; In 2012, another paper refuted
482
claims of previous ones that questioned the safety of sucralose, namely in stability in vivo,
483
chemical reactivity of sucralose, stability at high temperatures and interaction with
484
cytochrome P450 Shiffman and Abou-Donia, 2012. Recently, more controversy shattered
485
the public opinion, when in 2016 an article pointed out that consumption of sucralose
486
increases food intake through a neuronal fasting response Wang et al., 2016. The research
487
was carried out in Drosophila flies for their simple genome and fast replicating speeds.
488
Recently, in the same journal, Cell Metabolism, a new research implies the contrary, stating
489
that sucralose suppresses food intake, using the same test subjects. Another study, dated
490
2017 claimed that children, due to their lower weight and blood volume, have a higher
491
amount of sucralose in circulation, and that measures should be taken to determine the
492
security of this occurrence Sylvetsky et al., 2017; Park et al., 2017. These conflicting
493
results just bring more doubt towards the consumption of sucralose. A
B
495 496
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481
Figure 15. Molecular structure of sucrose (A) the precursor of the sweetener sucralose (B).
497 498
Table 3. Structure, ADI and sweetening power of the most common synthetic intense
499
sweeteners. Data extracted from Mitchell, 2006; Otabe, 2011c; Varzakas et al., 2012.
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ADI (mg/kg/day)
Brand Names
Sweetening power
Advantame - E 969
5
-
37000
Neotame - E 961
2
Newtame®
7000-13000
Sucralose – E955
5
Splenda®
400-800
RI PT
Name
Sweet and Low® Saccharin - E 954
5
Sweet Twin®
240-300
SC
Sweet N’Low® Nutrasweet® 40
Equal®
M AN U
Aspartame - E 951
200
Sugar Twin® Sweet One®
Acesulfame K - E950
9
150-200
Sunett®
EP
TE D
Assugrin®
AC C
Cyclamates - E 952
Chuker® Cologran® Hermesetas® Huxol®
11
Novasweet® Rio® Sucaryl® Sugar Twin® Suitli® Sweet N’Low®
500
30-80
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4.2. Natural intensive sweeteners
502
In recent years, the use of natural sweeteners has been increasing, mainly due to demand
503
from consumers. Even though natural organisms like the EFSA or FDA do not differentiate
504
sweeteners by synthetic or natural, being all sweeteners regulated by the EU normative
505
1129/2011.
RI PT
501
The most common natural sweeteners are steviol glycosides (E960), thaumatin
507
(E957) and neohesperidine dihydrochalcone (E959). Others, like tagatose and glycyrrhizin
508
also exist in the market but are not allowed to be used within the EU (Table 5).
SC
506
Steviol glycosides (E960) are molecules extracted from the leaves of Stevia
510
rebaudiana Bertoni, a plant from the Asteraeae family that is native from Paraguay and
511
Portugal. The plant has such a high concentration of steviosides that it can be directly used
512
as a sweetener (Lobete et al., 2017). The leaves are not allowed to be used in the EU, but
513
the purified, steviol glycosides compounds, are (Periche et al., 2015). They are extracted
514
with hot water and then recrystallized in a hydroalcoholic solution. Steviol glycosides
515
consist of mixtures of different compounds, namely stevioside (5-10%), rebaudioside A (2-
516
5%), rebaudioside C (1%), dulcoside A (0.5%), rebaudioside D, E and F (0.2%). Among
517
them, the sweetest compound is rebaudioside A (Gonzales et al., 2014; Momtazi-Borojeni
518
et al., 2016). The combination of these molecules has a sweetening power of over 300 times
519
sucrose and an ADI limit of 4 mg kg-1 of body weight per day. These molecules are
520
metabolized by the colonic bacteria, converting them to steviol glucoronides to finally be
521
excreted through urine. In terms of caloric contribution, it is neglectable, a thus safe for
522
diabetic patients, while properties like anti-inflammatory and diuretic effects are also
523
attributed to the compounds that comprise the mixture. Furthermore, it is relatively stable to
524
heat, can operate at a pH of 2 to 10. It displays a clean sweetness, although some of the
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components have a bitter taste. A small slice of the research concerning this sweetener has
526
shown concern about toxicity and genotoxicity of these compounds, although many authors
527
claim the database of in vitro and in vivo studies is robust and there is no indication of the
528
toxicity of stevioside and rebaudioside (Barriocanal et al., 2008; Brusick, 2008; Wheeler et
529
al., 2008). Recently, concerns about the endocrine disruption potential of steviol glucosides
530
has become a hot topic, with publications claiming there is a potential risk of these
531
compounds to have disrupting effects, suggesting further and deeper research on this
532
subject (Shannon et al., 2016; Urban et al., 2013, 2015). The uses of stevia encompass ice
533
creams, yogurts, cakes, sauces, drinks, bread, pastry, flavored milk, spices and as a tabletop
534
sweetener (Baines and Seal, 2012; Brandle et al., 2008; Carocho et al., 2015; Nabors (Part
535
I), 2001; Prakash and Chaturvedula, 2016).
M AN U
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525
A
OH
OH
OH
O
OH
O
O
TE D
O
OH
OH
EP
H3C
H
O
536
O
AC C
OH OH
OH
O
H CH3
OH OH
CH2
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M AN U
SC
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B
AC C
EP
C
TE D
537
538
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M AN U
SC
RI PT
D
539 540
Figure 16. The most representative compounds of steviol glycosides, namely stevioside
541
(A), rebaudioside A (B), rebaudiocide C (C), and dulcoside A (D).
542
Thaumatin (E957) is also a mixture of compounds, namely proteins, which are extracted
544
from the Thaumatococcus danielli Bennett plant, which is endemic to Africa (Baines and
545
Seal, 2012). It is a single-chain of 207 amino acid residues, which provide a sweet taste at
546
concentrations as low as 50 nM. There are other examples of sweet proteins, like monellin,
547
brazzein, and lysozyme, but thaumatin is the most widespread example of protein-based
548
sweeteners (Beauchamp, 2016; Firsov et al., 2016). The extraction is carried out with water
549
and mechanical processes, being the most important compounds Thaumatin A and B. In the
550
plant, these proteins display antimicrobial and protective functions, as sweeteners, they can
551
be 2,000 to 3,000 times stronger than sucrose, although the sweetness is quite slow to
552
develop and has a residual taste of licorice, thus being used in combination with other sugar
553
substitutes. In terms of stability, it has a high resistance to heat and acidic pH, while being
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very soluble in water. Furthermore, it has no caloric contribution and is very soluble in
555
water and stable at high temperatures (Baines and Seal, 2012; Pawar et al, 2013). It also has
556
a use as a flavor enhancer at a maximum of 0.5 mg kg-1, being used in food commodities
557
and supplements (EFSA, 2015). As a sweetener, it is approved both in the EU (since 1984)
558
and the US, where it is considered GRAS. Soups, sauces, processed vegetables and egg-
559
derived products are the main foods where it is used. Given the instabilities of its endemic
560
region in West Africa, and climate change, the production of thaumatin is not enough for
561
demand, therefore, many studies have focused on the production of recombinant thaumatin
562
through microorganisms and transgenic plants (Jain and Grover, 2015; Masuda, 2016;
563
Nabors (Part I), 2001).
566
SC
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565
Figure 17. Representation of the protein thaumatin created with PYMOL software.
AC C
564
RI PT
554
567
Neohesperidin dihydrochalcone (E959) is another intense semi-natural sweetener that
568
comes from the skin of the immature fruits of Citrus aurantium L. When extracted, this
569
compound is a flavone, neohesperidin, which after suffering hydrolysis becomes a
570
dihydrochalcone (Baines and Seal, 2012). Other method to obtain neohesperidin
571
dihydrochalcone is through synthesis of naringenin, extracted from the fruit of Citrus
572
paradise Macfad. This sweetener is reasonably hygroscopic and is stable at high
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temperatures, namely during pasteurization, but quite insoluble, and presents an off-white
574
crystalline powder, although being poorly soluble in water at room temperature but highly
575
soluble in hot water (Nabors (Part I), 2001). This fact is attenuated by the low quantities
576
needed in food, and the fact that it is used in combination with polyols or glucose syrup. Its
577
sweetening power, although quite high is far from the most potent ones, achieving only
578
1,500 times stronger than glucose, and also has a very slow sweetening speed and a
579
menthol residue. One of its functions when used with other sweeteners is to mask their
580
unwanted tastes. It has a high ADI, of 35 mg kg-1 of body weight per day and does not
581
accumulate in tissues given to its quick metabolization and excretion (EFSA, 2011).
582
Approved in the EU since 1994 but not in the US. This natural sweetener is also used to
583
thicken liquid foods, so it is used for ice creams, bubble gums, pastry, water-based flavored
584
drinks, milk and derivatives, snacks, confectionary foodstuffs, beer, soups, food
585
supplements and as a tabletop sweetener and fruit derived food (El-Samragy; Spillane,
586
2006).
587 588 589
AC C
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573
Figure 18. Chemical structure of neohesperidin dihydrochalcone.
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Glycyrrhizin, or more correctly glycyrrhizinic acid is a triterpenoid saponin that is obtained
591
from the roots and rhizome of Glycyrrhiza glabra, a plant known as licorice. It is described
592
as being from 30 to 200 times sweeter than sucrose. Apart from this, it is also recognized
593
for having several pharmacological and biological activities, namely anticancer, anti-
594
inflammatory, hepatoprotective, antioxidant and antiviral. In the US, glycyrrhizin is
595
considered GRAS although there is a guideline for the maximum permitted levels for the
596
saponins on several preparations (Karkanis et al., 2016). In the EU, although the
597
Commission Report states that the consumption is safe, a limit of 100 mg per day is
598
recommended, given the glucocorticoid effects id the glycyrrhetinic acid present in the
599
extract. Still, given that the use of this extract is not widespread, these levels are related to
600
the consumption as licorice rather than a sweetener (Komes et al., 2015). One drawbacks of
601
using glycyrrhizin is the potential hypertensive effects. Still, it has been used previously in
602
candies, chewing gum, toothpaste, beverages and tobacco. Furthermore, its specific aroma
603
and intense aftertaste are reasons that it has not been very widespread (Graebin, 2016;
604
Omar et al., 2012).
SC
M AN U
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EP AC C
605
RI PT
590
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O HO
H OH
RI PT
O
O
O OH H O OH
O H
O
SC
O
HO OH
OH
607
OH
M AN U
606
Figure 19. Representation of glycyrrhizin.
608
Tagatose is a ketohexose that is structurally similar to lactose, displaying a hydroxyl
610
group in C4, and can be found in small quantities in fruits (cacao) and in dairy products. It
611
is obtained from lactose, though an enzymatic process followed by an isomerization and
612
purification steps. It displays a staggering 92% of sweetness potency, but with only one
613
third of the calories, making it interesting for sweetening food (Bell, 2016; Jayamuthunagai
614
et al., 2016). Even though it is considered a sugar, it does not promote tooth decay.
615
Furthermore, tagatose, by having a different metabolization to sucrose, does not interfere
616
with blood glucose levels, deeming it safe for diabetic individuals. Of all the consumed
617
tagatose, only 20% is absorbed by the intestine and readily excreted in urine (Ensor et al.,
618
2014; Lu et al., 2007; Tandel, 2011; Levin, 2002). Although tagatose is naturally occurring,
619
its production is now industrialized (through enzymatic reactions), making its classification
620
as a semi-synthetic compound in foodstuffs, and rendering a colorless crystalline powder
621
with a bitter aftertaste, but compatible with a wide range of food ingredients It has
AC C
EP
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609
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considerable advantage when compared to other natural and synthetic sweeteners since it
623
can be considered a prebiotic and has a similar taste to sucrose (Dobbs and Bell, 2010; Oh,
624
2007). It is stable at pH 2 − 7, displays a high solubility in water, making it ideal to also be
625
used as a flavor enhancer, although it lacks some stability. Furthermore, it shows humectant
626
behavior like sorbitol, but decomposes faster than sucrose at high temperatures. Tagatose is
627
approved in New Zealand, Korea and in the EU, although its use in the EU is not as a
628
sweetener, rather as a food ingredient. In the USA, it is considered GRAS and can be used
629
as a low-calorie sweetener. Its applications encompass beverages, cereals, bubble gum,
630
chocolate, caramels yogurts, ice creams, nutritional supplements, and candy. Some
631
conflicting results have been found regarding its effects on gastrointestinal unrest.
632
Genotoxic studies have been carried out and determined tagatose as non-genotoxic (Baines
633
and Seal, 2012; Kim, 2004; Nabors (Part I), 2001).
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B
635 636 637 638
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Figure 20. Lactose and tagatose
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Table 5. Natural intense sweeteners, ADI, structure and sweetening power ADI (mg/kg/day)
Brand Names
Sweetening power
Thaumatin - E957
50
-
2000
Neohesperidine dihydrochalcone – E959
35
-
1500
RI PT
Name
Truvia®
Steviol glucosides - E960
4
PureVia®
300
Glycyrrhizin
Not specified
SC
Enliten®
M AN U
Not considered a food Tagatose
-
100
-
0.92
additive
640 641
5. Conclusions and Future perspectives
The WHO directives state that sugar should not represent more than 10% of the
643
daily caloric contribution, and is preparing to propose a reduction to 5% in the near future
644
(Mooradian et al., 2017). This is a huge burden and at the same time an opportunity for the
645
food industry, governments and consumers! For one, the opportunity to reduce the
646
consumption of sugar is beneficial, lowering the health issues associated with its excess
647
consumption, translating in a reduction of health spending by governments. On the other
648
hand, stronger and more effective sweeteners are necessary to be added to food to carry out
649
sweetening functions without increasing the quantity of added sweetener, due to legal
650
restrictions and the alleged health implications of sweeteners.
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The recent discovery that non-caloric sweeteners also seem to increase the
652
prevalence of diabetes and weight, unravels a grim future for patients with sugar
653
restrictions and the average consumer, whom cannot be free from the dangers of eating? Or
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is research “simply just seeking to deep?” Is research trying to find, at all costs, culprits for
655
sicknesses, and links between sweeteners and illnesses? (Fowler et al., 2008; Imamura et
656
al., 2015; Koning et al., 2011) Could some of these metabolic disorders happen to be, like
657
cancer, which recent studies state that two thirds of carcinomas are a matter of “luck” rather
658
than lifestyle or gene disorders? What will be the fate of eating in the beginning of the
659
century? (Nowak and Waclaw, 2017; Tomasetti and Vogelstein, 2015).
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Further entropy arises when similar studies end up in conflicting results. One
661
incredible example is detailed by Bes-Rastrollo et al. (2013), in which similar studies found
662
contradicting results. In one, funded by food industry companies, in 83% of studies stated
663
that insufficient proof was detected for a correlation among the consumption of sugar-
664
sweetened beverages and weight gain, while in other studies, without industrial financing,
665
the same percentage could relate the increase in weight with the consumption of such
666
beverages.
667
researcher, especially clinical investigators when carrying out their research while being
668
funded by enterprises. The risk of biased reports in the food industry is continuous, given
669
the different ways associations of enterprises and researchers can be achieved, namely
670
through sponsorships of journals and conferences, sponsorships of research studies,
671
partnerships and alliances. Although there is always a latent risk in virtually all areas,
672
because advances in industry come from research, tight regulation is critical to avoid these
673
types of occurrences that just discredit both the industry and research (Boyd et al., 2003;
674
Nestle, 2001).
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Even before this study, uncomfortable positions have been identified by
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After a “not so peaceful” coexistence between consumers and sweeteners, fueled by
676
scandals, legislation gaps and controversies, and occasional deception by the industry, the
677
public wants to be assured that they are consuming safe sweeteners. There are many forms
ACCEPTED MANUSCRIPT
to induce trust in consumers, but they rely on combined efforts from the industry,
679
governments, press/media and consumers. The industry must, at all costs research and
680
produce safe, sound, cheap, easily producible, sustainable and strong sweeteners.
681
Governments must act in two manners. Firstly, combining efforts to avoid legislation gaps
682
and harmonizing legislation across the many governing bodies (EFSA, FDA…), which can
683
be an incredible leap in gaining consumer trust. In the XXI century, it is unthinkable that
684
cyclamates and neohesperidine dihydrochalcone are allowed in the EU and not in the US,
685
while D-tagatose is not considered a sweetener in the EU and cannot be used as one, if the
686
scientific background is available for both governing bodies to consult and legislate
687
accordingly. Why the legislation difference? The second effort that could be put forward by
688
governments is the public education regarding eating, healthy lifestyles and choices. The
689
press and media play a role in the scandals, speculation and exaggeration of studies and
690
legislation, and should tone down when disseminating information that can be badly
691
interpreted by the public, especially the uninformed fringe. Finally, the consumer must, at
692
all costs seek trustworthy information to make informed decisions about what they are
693
eating. In the era where information is everywhere, finding reliable information can be the
694
difficulty, but scientific publications are somewhat easier to find as they tend to become
695
open source. Reading the article or study that originated a news article is always better than
696
to read the news itself, for the scientific reports are stripped from exaggeration and
697
extrapolation, conveying specific findings.
SC
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EP
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698
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What are the next generation of sweeteners, and how are they going to affect the
699
population is the question to be asked. There should be a constant seek for new low caloric
700
sweeteners, namely isomers of known ones and other related compounds that have should
701
have higher sweetening powers, lower production costs, lower caloric contribution and no
ACCEPTED MANUSCRIPT
health impact. Concomitantly, the major investment should be on both synthetic and natural
703
non-caloric sweetener. The synthetic molecules will be rearrangements of known
704
sweeteners or prospection for new ones, relying on combinatorial chemistry, but also the
705
improvement of the production of widespread sweeteners. The answer to passing the idea
706
of safety could be the production of these compounds through ecological and sustainable
707
processes, translating in a better understanding of the public, while associating sweeteners
708
with eco-friendly and safety ideas. The marketing of studies that deem artificial sweeteners
709
safe is critical to, through scientific discovery inform consumers that they are consuming
710
safe chemicals. The natural sweeteners financing will be for better extraction methods of
711
currently impracticable compounds and the discovery of new sources of sweetening
712
molecules. Natural sweeteners have been becoming more widespread due to the public’s
713
perception that what is natural is less hazardous for health, and both manufactures and food
714
companies have started to shift considerable amounts of funds to new natural sweeteners.
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Further innovations in the sector could arise from new types of sweeteners or
716
improvements. Compounds like miraculin, which is not a sweet molecule, but alters taste
717
buds to perceive food as sweet could be improved while, other similar molecules can be
718
found in nature or synthesized and used in the food industry. These molecules or extracts
719
could be added to food to make it be perceived as sweet, rather than making them actually
720
sweet, ultimately avoiding alleged health impacts from sweeteners.
AC C
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Although some improvements and innovations may seem temporally closer than
722
others, the truth is that the sweeteners market, mainly regarding sweeteners as food
723
additives, will be suffering changes and having to tackle health and economic issues, while
724
coping with regulation that should become more harmonic to ensure trust and peace of
725
mind for consumers, because the reduction of sugar intake seems imminent and necessary.
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By 2020, EFSA will be providing scientific advice of added sugar in food, establishing a
727
science-based cut-off value for daily exposure to added sugars from all sources which is not
728
associated with adverse health effects. This means that the concerns about sugar’s effects
729
on health are real, making this an opportunity for the sugar substitutes to become safer,
730
trustworthy, and, expectedly sweeter.
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731
Acknowledgments
733
The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) and
734
FEDER under Programme PT2020 for financial support to CIMO (UID/AGR/00690/2013).
735
Author
736
SFRH/BPD/114650/2016.
Márcio
Carocho
also
737
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thanks
FCT
for
his
Conflict of Interest
739
The authors state no conflicts of interest regarding the manuscript.
740
grant
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post-doctoral
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ACCEPTED MANUSCRIPT HIGHLIGHTS Sweeteners are essential to reduce caloric intake in diets Some sweeteners are still seen with distrust by consumers Natural sweeteners are gaining interest from consumers and companies There are still some legislation discrepancies among the EFSA and FDA concerning sweeteners
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• • • •
S0278-6915(17)30364-2
DOI:
10.1016/j.fct.2017.06.046
Reference:
FCT 9153
To appear in:
Food and Chemical Toxicology
Received Date: 23 May 2017 Revised Date:
26 June 2017
Accepted Date: 28 June 2017
Please cite this article as: Carocho, Má., Morales, P., Ferreira, I.C.F.R., Sweeteners as food additives in the XXI century: A review of what is known, and what is to come, Food and Chemical Toxicology (2017), doi: 10.1016/j.fct.2017.06.046. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Sweeteners as food additives in the XXI century: A review of what is known, and what is to come Márcio Carochoa, Patricia Moralesb*, Isabel C.F.R. Ferreiraa* Mountain Research Centre, (CIMO), ESA, Polytechnic Institute of Bragança, Campus
de Santa Apolónia, 5300-253, Bragança, Portugal b
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Department of Nutrition and Bromatology II, Faculty of Pharmacy, Complutense
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University of Madrid, Plaza Ramón y Cajal, s/n, 28040, Madrid, Spain
* Corresponding authors: Patricia Morales (email: [email protected];
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[email protected]; Telephone: +351-273-303219; fax +351-273-325405)
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1. Introduction Mankind experiences the world through its five primary senses, and interprets the
3
inputs with reason and emotion. This fragile human condition makes humans tend to prefer
4
some stimuli, and hate other types of negative sensations (Mooradian et al., 2017). With
5
regard to taste, it is widely known that children prefer sweet taste over the other basic
6
flavors, and although this can change with age, sweet taste is still one of the most desired
7
flavors for mankind, preferred over sour and bitterness (Kim et al., 2017). Research deems
8
this preference as innate and linked it to sensations of pleasure and happiness. Moreover,
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other studies have proven that sugar craving could be genetic, making some individuals
10
struggle with adverse effects of overconsumption of sweet food (Drexler and Souček, 2016;
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Padulo et al., 2017).
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In a profit driven economy, the food industry finds new ways to lure consumers to
13
consume their products, paying little attention to the potential health effects of the
14
cumulative consumption of various food products throughout the day. Thus, especial
15
attention should be given to children and toddlers, for they are unaware of the
16
consequences (Hert et al., 2014). For many years, the consumption of excessive sugar is
17
known to have adverse effects in humans, and thus, to reduce its intake, sweeteners
18
appeared back in the 1800’s. Since their inception, sweeteners have come a long way, and
19
while they were once regarded as one of the most important achievements for the food
20
industry, many controversies, conflicting regulations and laws have deemed them to
21
untrusted molecules that are added to food to make it sweeter. Today, metabolic disorders
22
are increasing, obesity is increasing, and so are diabetes and other diseases that are directly
23
related to sugar consumption, in fact, the WHO studies have considered metabolic disorders
24
as being of “epidemic proportions” in industrialized countries (Pradhan, 2007; Rani et al.,
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2016). With the increasing prevalence of diseases related to sugar consumption, sweeteners
26
are now widespread in foodstuffs, and are highly researched for their impact on sweetening
27
potentials, on health, on the economy and in social studies (Mooradian et al., 2017). In this article, the authors review the sweeteners state of the art (classes, behaviors,
29
applications, benefits, disadvantages, scandals, and corporative tactics), and postulate future
30
trends in food sweetening.
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2. General considerations
The most important aspect of sweeteners is undoubtedly their sweetness; it is
34
measured in relation to sucrose, which is the reference sugar. Thus, a solution of 30 g L-1 at
35
20 ºC has a sweetening power of 1, with the threshold of the minimum concentration to
36
detect sugar being 1-4 mM. For the sweet flavor intensity to be perceived, the substance
37
must first be dissolved in saliva and come into contact with the receptors that are present on
38
the tongue. Other parameters influence the sweet flavor, namely the sugar structure (in
39
which the intensity decreases as the number of monosaccharides increase), temperature of
40
perception, pH and the presence of other molecules that can influence receptors.
41
Taking sucrose as a reference (its reference value can be considered 1), it has a higher
42
sweetening power when compared to other simple sugars, for instance, galactose (0.3),
43
while others show higher values, namely fructose (1.7). Furthermore, there are other highly
44
complex sweeteners that have thousands of times the sweetening power of sucrose,
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neotame (13,000 times sweeter) or even advantame, which is 37,000 times stronger than
46
sucrose (Table 1) (Ordoñez et al., 1998).
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Table 1. Difference of sweetness among different molecules, calculated based on the
49
assumption that sucrose is equivalent to 1 unit of sweetness. Data extracted from Mitchell,
50
2006; Otabe, 2011c; Varzakas et al., 2012. Sweetening power
Advantame
37000
Neotame
7000-13000
Neohesperidin
1500-2000
Sucralose
400-800
Saccharin
240-300
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Aspartame
200
Acesulfame-K
150-200
Cyclamate
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Fructose
1.1-1.5
Sucrose
1
Xylitol
1
Dextrose
0.9
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Sweetener
Maltitol
0.75
Glucose
0.75
Erythritol
0.7
Mannitol
0.6
Sorbitol
0.6
Isomaltose
0.55
Maltose
0.4
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Lactitol
0.35
Galactose
0.3
Raffinose
0.2
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Biologically, the perception of sweetness happens through the receptors on the taste buds,
53
based on a donor/acceptor proton system, establishing an AH/B/X system between the food
54
and the receptors of the taste buds. A and B are electronegative atoms, like oxygen or
55
nitrogen, H represents hydrogen, which is connected to an atom (A) through a covalent
56
bond. X represent hydrophobic groups that are attracted by the taste buds in order for the
57
AH/B/X to become tridimensional. The receptors of the taste buds are coupled to G
58
proteins (T1R2 and T1R3), forming part of the C class of proteins (GPCR), which are
59
structurally similar to the glutamate metabotropic receptors. The bond between sweet
60
molecules with the AH/B/X structure with these receptors happens through hydrophobic
61
hydrogen bonds. This bond changes the configuration of the “taste sensible” receptor,
62
altering the permeability of the ionic environment, aiding the entrance of Na+
63
(Shallenberger and Acree, 1971). For a compound to display a sweet taste, the molecular
64
distance between A and B must be at least 0.25 to 0.40 nm. The sensation of sweetness also
65
depends on the configuration of the molecule, which in sugars comes from the dextrorotary
66
conformations, but not from the inverse, levorotary. For this reason, some sugars, like
67
cellobiose are insipid, but others are sweet (D-glucose), while L-glucose is slightly salty.
68
The three-dimensional structure of D-glucose binds to the receptor with the hydroxyl group
69
of C4 (AH function) and the oxygen in C3 (B function), together with the hydroxyl group
70
of C6, they bind to the receptor through hydrogen bonds (Crammer and Ikan, 1979;
71
Lindemann, 2001). The activation of such receptors by sweet substances releases adenosine
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triphosphate (ATP) that consequently activates neurons that transmit this input to the brain.
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Apart from depending on physical and chemical properties of the substances, sweet flavor
74
is also determined by differences in humans, namely age, genetics, race and ethnicity
75
(Nelson et al., 2001; Ohtsu et al., 2014; Smutzer et al., 2014; Weerasinghe and DuBois,
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2006).
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3. Classification, properties and sweeteners role in food
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Sweeteners (as legal food additives and non-additives) can be classified by intrinsic
80
properties or origin. Some of the most common classifications are in terms of their nutritive
81
value, sweetening power and their provenance. Thus, they can be divided in nutritive vs.
82
intensive sweeteners (Figure 1A and 1B), but also between synthetic and natural origin
83
(Figure 2). While the former is a classification used by governing bodies like the European
84
Food Safety Authority of the European Union (EFSA) the division in natural and synthetic
85
food additives is not used by these organizations, and is based solely on the origin of the
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sweetener.
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A
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Figure 1. A – Examples of nutritive sweeteners. B – Examples of intensive sweeteners.
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Figure 2. Examples of synthetic and natural sweeteners.
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In the nutritive sweeteners group (Figure 1A) are the simple sugars but also high
98
fructose corn syrup, isomaltulose, trehalose, which, under the Regulation (EU) No
99
1333/2008 cannot be considered food additives, but ingredients. Furthermore, polyols
100
(which are considerd as food additives) are also included in this classification; examples of
101
polyls are erythritol, isomaltitol, lactitol, maltitol, sorbitol, mannitol, and xylitol. On the
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other hand, the intensive sweeteners, all of them considered as food additives (Figure 1B),
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have negligible caloric contribution and high sweetening capacity, being used in low
104
quantities in food. Generally, they are not cariogenic and do not trigger glycemic response,
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thus being extensively used in hypocaloric diets, for diabetes patients and other specific
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cases where caloric intake must be controlled (Baines and Seal, 2012; Varzakas et al.,
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2012).
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The other classification, presented in Figure 2. divides sweeteners by their nature or origin,
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which can be either synthetic or natural. Sucrose, a disaccharide, the most used table sugar, known commonly as sugar and
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the most used sweetening agent in the world. It is composed of a molecule of glucose in
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which the aldehyde carbon is joined to the ketone one of fructose, forming a b(1,2) bond,
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preventing any reducing properties and forming an adequate structure to bind to the taste
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bud receptors, conferring the traditional sweet taste. For some time now, the relation
115
between the consumption of this sugar and dental decay has been established, given that it
116
is the substrate for bacteria, like Streptococcus mutans and S. sanguis that use this
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disaccharide and convert it to pyruvic, acetic and lactic acid, which dissolve the tooth
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enamel, fostering bacterial colonization. Furthermore, the very fast absorbance of sucrose
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can make glycemic values spike, causing hormonal problems, thus the danger if its
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consumption by some diabetic patients (Valdés-Martínez, 2006). Other diseases and
121
disorders are also related to sugar consumption, among them are cardiovascular diseases
122
(coronary), type II diabetes, metabolic syndrome, hypertriglyceridemia, insulin resistance,
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cancer (breast, colon), obesity, childhood obesity, hypertension and kidney diseases
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(Bostick et al., 1994; Grundy, 1999; Johnson et al., 2007; Ludwig et al., 2001; Mente et al.,
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2009; Slattery et al., 1997; Stanhope et al., 2013; Touger-Decker and van Loveren, 2003;
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Yang et al., 2014).
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For these reasons, the role of sweeteners has been paramount in the dichotomy of
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food and health, and their impact on our daily life, longevity and quality thereof is
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staggering. Thus, the changes of food consumption have been drastic, with sweeteners
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chugging alongside the industrialization of food and food components, being their
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discovery a revolution in the food sector. This allowed the production of sweet food
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without caloric intake, changing the paradigm of how we eat, and of vital importance to
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people with hypocaloric diets and diabetics. For the latter, polyols, for instance, as like
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fructose, display a metabolization that is independent from insulin, given that they may
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enter the hepatic cells through the action of the enzyme fructocinase, which is independent
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from insulin, which also deems them safe for these patients. Furthermore, many sweeteners
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are not cariogenic, so they are not used as subtract for oral bacteria.
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Some of the most used sweeteners worldwide are aspartame (E951), cyclamates
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(E952), acesulfame K (E950), tagatose (considered “generally regarded as safe” (GRAS)
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by the Food and Drug Administration of the United States of America (FDA)), sucralose
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(E955) and more recently steviol glucosides (E960).
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3.1. Polyols: Classification and applications
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Polyols, polyhydric alcohols or polyalcohols, are food additives that result of the
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hydrogenation of reducing sugars, being the presence of an alcohol group in the place of the
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carbonyl group quite common in the aldose or ketose fractions of mono, di, oligo and
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polysaccharides. Polyols are stable at high temperature, pH changes and do not intervene in
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Maillard reactions. They can be found in nature, especially in fruit and vegetables, being
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partially responsible for their sweetness. Their industrial production started in the 20’s with
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hopes of solving health problems related to excessive sucrose consumption. Nearly 90
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years after, polyols are the most consumed group of sweeteners because of their lack of
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cariogenic properties, salivation induction, and no interference in insulin levels, being used
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in “light” foods (Nabors, 2001 (Chapter II); Varzakas et al., 2012). On the other hand, their
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consumption is not recommended for toddlers under 1 year of age, due to their laxative
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effects that can unleash severe diarrheas. Technologically, polyols are also important,
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namely for reduction of water activity, as humectants, inert to Maillard reactions,
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texturizing agents, sugar crystallization mediators, flavoring solubilizers, and so on. When
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being used for these purposes, they are labelled quantum satis (latin for “just far enough”
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meaning that there is no limit for its use, as long as the least amount for the specific
160
outcome is used) (EU Regulation 1333/2008; EU Regulation 1129/2011). The most used
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polyols are sorbitol (E420), mannitol (E421), isomaltose (E953), maltitol (E965), lactitol
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(E966), xylitol (E967), erythritol (968). Less used, but also with relevance are arabitol and
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hydrogenated starch hydrolysates (HSH), although not allowed within the EU.
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Sorbitols (E420) and mannitols (E421) are isomeric polyols and have been use in
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food since the 40’s through glucose syrups, inverted sugars and other hydrolyzed starches.
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Their production is based on the catalytic hydrogenation of glucose with subsequent
167
purification. The separation of the isomers is done by solubility difference, yielding a very
168
hygroscopic sorbitol and a much less mannitol. Sorbitol is 50 to 60% sweeter than
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mannitol, making it preferably used as sweetener, while mannitol is employed as an anti-
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caking agent (Song and Vieille, 2009). Overall, these polyols are used in baked goods,
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sweets, bubble gum, surimi, sausages and drinks (Nabors, 2001 (Part II)). Although there is
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no evidence of sorbitol toxicity, in 2016, a study found that sorbitol can be genotoxic and
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induce metabolic reactions in offspring of female wistar albino rats fed sorbitol. A study
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found that patients with irritable bowel syndrome (IBS) have adverse gastrointestinal
175
reactions to polyols, especially sorbitol and mannitol, being these reactions independent of
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the absorption patterns of each molecule. While sorbitol can be of concern for patients with
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IBS, it seems to be safe for healthy individuals, although there are reports of laxative
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effects when consumed in high doses. Some studies point out that this effect is related to
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the fructose:glucose:sorbitol ratio that is consumed, and not to sorbitol itself (Hoekstra et
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al., 1993; Yao et al., 2014). Mannitol, although less sweet than sorbitol is also used in food,
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given its high metabolization ratio, about 75%, being the other 25% absorbed before being
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excreted in urine. Because it is virtually inert, it does not react with active components of
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drugs and confers a cool sweet taste, apart from being used in the food industry, it is also
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widely used in the pharmaceutical area in dental hygiene products, drug filler and as a
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diuretic in intravenous fluids (Biesiekierski et al., 2011; Lee, 2015; Livesey, 2003;
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Mitchell, 2006;). B
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Figure 3. Chemical structure or sorbitol (A) and mannitol (B).
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Isomaltose, isomaltitol, or isomalt (E953) in a legal polyol in the EU and the USA,
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obtained through enzymatic transformation of sucrose (Cammenga and Zielasko, 1996). It
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is stable at high temperatures and has a very low hygroscopic value. Its sweetening power
193
is in line with other polyols, about 45 to 60 % of sucrose, but a very low caloric
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contribution, of about 2 kcal g-1. This molecule is not absorbed by the small intestine, and is
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readily fermented in the colon through colonic bacteria (Caballero et al., 2016). Isomalt is
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used in bubble gums, gelatins, chocolate, coatings, baked goods and yogurts, among others
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(Grenby, 1996; JECFA, 2003).
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Figure 4. Chemical structure of isomaltose.
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Lactitol (E966) is a disaccharide that is obtained by hydrogenation of lactose. It was
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discovered around 1920 and since then has been used in many different foods. Given its
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limited sweetening power compared to the other polyols it is usually used in combination
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with intense sweeteners, like acesulfame K, aspartame and sucralose. The human body does
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not metabolize this polyol, therefore it has no caloric contribution (Mitchell, 2006). Still, it
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only has a sweetening power of 30 to 40 % of sucrose and a lower solubility that xylitol
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and sorbitol. Its taste, apart from being sweet gives a fresh aftertaste, and is therefore used
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to confer different kind of sweetness to food. Furthermore, it is also used to increase food
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volume, as a probiotic, while also not being cariogenic. Lactitol exists in four crystallized
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crystalline forms: anhydrous lactitol, lactitol monohydrate, lactitol dehydrate, and lactitol
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trihydrate, being the anhydrous the most stable form of this compound. The foods it is used
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in are chocolates, baked goods, bubble gums and ice creams (Aidoo et al., 2013; Grenby,
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1996; Halttunen et al., 2001; Mitchell, 2006).
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214 215
Figure 5. Chemical structure of lactitol.
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Maltitol (E965) is obtained by hydrolyzation, reduction and hydrogenation of starch,
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resulting in a sweetener with about 90% of sweetening capacity, no other residual flavors
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and very high stability (Maguire et al., 2000; Pratt et al., 2011). Of all the sugar alcohols, it
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is the one that most resembles the flavor of sugar. It is not cariogenic and safe for diabetics.
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In terms of solubility and hygroscopicity it is very similar to sucrose, thus being the
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preferred sugar to use in the production of chocolate in which the label says “no sugars
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added” (Joshi, 2016). It has a very slow digestion rate, being fermented in the colon. Apart
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from chocolates, it is also employed in lactic products, baked goods, muffins, bubble gum,
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jams, jelly and other sweets (Grenby, 1996; Mitchell, 2006;).
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Figure 6. Chemical structure of maltitol.
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Xylitol (E967), a five-carbon polyol, obtained by hydrogenation of xylose, was first
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synthesized in 1891 and has about 95% the sweetness of sucrose. Of all the polyols, it is the
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sweetest, contributing only 2.4 kcal g-1. This compound is obtained by extraction from
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birch and other woods, almond husks, corncobs, straw and paper production surplus. Apart
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from this, and although not viable for industrial production, xylitol is also found in many
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fruits and vegetables (Nabors, 2001 (Part II); Mitchell, 2006). It is known to increase
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salivation, thus increasing teeth cleansing and reducing the bacterial load in the mouth and
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therefore teeth decay. Xylitol is used in bubble gum, refreshments, baked goods, among
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others. It is estimated that this sweetener has a market of 670 million dollars worldwide,
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which has been increasing 6% per year, and is expected to continue growing until 2020.
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These figures, in line with what is happening transversally to all food additives, represent
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the increasing awareness of naturally derived food additives (Dasgupta et al., 2017;
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Mitchell, 2006; Peterson, 2013).
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Figure 7. Chemical structure of xylitol.
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Erythritol (E968), used legally both in the EU and the USA, appears naturally in some
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fruits (melon, pears and grapes), but also in vegetables, mushrooms, honey and seaweeds,
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but its primary method for industrial production is through yeasts (Boesten et al., 2015
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Tomaszewska et al., 2014). Being discovered in 1848, today it takes part in a multitude of
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products, like food coatings, baked goods, fermented milk, glazed goods, candy, and
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chocolate (Carocho et al., 2015). Its sweetening power is about 60 to 80% of that of sucrose
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and a very low caloric contribution, of just 0.3 kcal g-1, therefore being safe for diabetics.
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Furthermore, erythritol is easily absorbed through the intestine and has a very low
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metabolization, being almost completely excreted in urine (Arrigoni et al., 2005; Röper et
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al., 1993). Erythritol is considered as a safe additive after many specific tests regarding
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toxicity, carcinogenicity and reproductive hazards resulted negative, although in 2013,
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there was report of an 11-year-old child that had erythritol induced anaphylaxis (Shirao et
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al., 2013). This sweetener also displays antioxidant capacity and has protective endothelial
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properties (Boesten et al., 2015).
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Figure 8. Chemical structure of erythritol.
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Apart from these polyols, there are others, although these cannot be used in food inside the
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EU, namely arabitol, which is obtained by reduction of arabinose, and HSH, which is a
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mixture of polyols that can achieve about 90% of sweetening power. In the USA, these
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sweeteners are legal, and actually considered GRAS food additives. Arabitol has a very
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similar structure to sorbitol (6-carbon skeleton) and is used for its rheological properties,
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viscosity improvement, humidifying, crystallization and rehydration properties of the
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foodstuff it is used in (Carpentier et al., 2013; Modderman, 1993). HSH are a family of
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bulk nutritive sweeteners that comprehend hydrogenated glucose, maltitol and sorbitol
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syrups. They were first developed in the 60’s in Sweden and have been used in foodstuffs
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since then. They are produced by hydrolysis and hydrogenation of corn, wheat or potato
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starch, and a caloric contribution of 3 calories per gram, not causing tooth decay.
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Furthermore, HSH can be used as viscosity and bodying agents, humectants, crystallization
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modifiers and rehydration aids. (Larry and Greenly, 2003). On Table 2 some of the most
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important polyols used in food are displayed, along with their chemical structure and
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caloric contribution per gram.
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Figure 9. Chemical structure of arabinose (A), the precursor of arabitol (B).
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Figure 10. Chemical structure of hydrogenated starch hydrolysates.
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Table 2. Most used polyols and caloric contribution in kcal g-1. Data extracted from
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Varzakas et al., 2012.
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Caloric Name contribution
Hydrogenated starch hydrolysates
2.8
Maltitol - E 965
2.7
Sorbitol - E 420
2.5
Xylitol - E 967
2.5
Isomaltose - E 953
2.1
Lactitol - E 966
2
Mannitol - E 421
1.5
Erythritol - E 968
0.2
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4. Intensive sweeteners
Intensive sweeteners are those that present a high sweetening power, higher than
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sucrose, thus only being necessary in very low doses to obtain intense sweetness. Their
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caloric contribution is also very low or even virtually zero, they also present no danger in
290
terms of cariogenicity or insulin reaction and have no other function in food apart from
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sweetening.
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4.1. Synthetic intensive sweeteners
Among all the intense sweeteners used in the industry, the most notable ones are
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acesulfame K (E950), aspartame (E951), cyclamates (E952), saccharin (E954), sucralose
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(E955) and neotame (E961), which are detailed in Table 3. Recent research has showed the
297
impact of neural mechanisms involved in the sweet taste, and related that, like all things
298
sweet, sweeteners modulate neural systems, perpetuating their intake, although in different
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manners. Both caloric and non-caloric sweeteners act on the reward mechanisms, and in
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situations of caloric deficit, caloric sweeteners excerpt stronger craving. Thus, non-caloric
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sweeteners potentially act with lower intensity in neuronal paths of reward, but is their
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contribution to health and industry innocuous? Probably not… Recent studies suggest that
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non-nutritive sweeteners can, surprisingly, be related to weight gain and type 2 diabetes
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risk through 3 potential mechanisms: a) interference with learned responses that contribute
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to control glucose and energy homeostasis; b) interference with the gut microbiota,
306
inducing glucose intolerance; c) interaction with sweet-taste receptors that may trigger
307
insulin secretion (Murray et al., 2016; Pepino, 2015).
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Acesulfame K (E950) corresponds to the potassium salt of acesulfame, and was
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discovered in 1967, although today, its industrial production has changed, being obtained
310
through sulfamic acid and deketene which will eventually produce sulphur. Acesulfame K
311
is one of the most used synthetic sweeteners due to the lack of residual flavors and a
312
sweetening power of over 200 times the one of sucrose. It can be used in synergies with
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other sweeteners, namely aspartame, cyclamates and sucralose to further improve
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sweetening and flavor. Unlike polyols, this compound suffers metabolization by the human
315
body, thus having an admissible daily intake (ADI) of 15 mg kg-1 of body weight. The ADI
316
is the maximum amount of a compound that can be ingested per kg of body weight per day,
317
considering all the sources of the compound. Many studies have described its
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innocuousness, although other studies up until 2000 pointed some type of toxicity, but were
319
then disproved (Carocho et al., 2014; Shankar et al., 2013). Still, studies carried out by
320
Stohs and Miller (2014) claim that there is some type of hypersensitivity at a dose
321
dependent manner. Acesulfame K is used in baked goods, cereals, sweets, confectionary
322
products, marmalades, canned food and fruit, bubble gum and as tabletop sweeteners (for
323
coffee and others) (Nabors (Part I), 2001; Mitchell, 2006; O’Donnell and Kerasley, 2012).
324
A new problem related to acesulfame k and other synthetic sweeteners is their ubiquity in
325
the environment given the high amounts that are consumed by populations and excreted
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into wastewaters. Thus, a considerable amount of research groups are trying to find new
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ways to inactivate this contaminant, for it is excreted unaltered due to the lack of
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metabolization in the human body. In surface waters, its concentration can achieve 1 µg L-1,
329
which is higher than the concentration of the average contaminant. The major problem is
330
that the residue produced by its inactivation is more toxic than acesulfame k itself, which
331
consists of yet another challenge to the food/environmental industries with regard to
332
synthetic food additives (Yin et al., 2017). B
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Figure 11. Chemical structure of sulfamic acid (A) and acesulfame K (B).
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Aspartame (E951), discovered in 1965 is obtained through the combination of amino acids,
337
namely L-phenylalanine, L-aspartic acid, and connected through methyl ester bonds. Given
338
is extremely low solubility in water and unstable pH it cannot be used in refreshments with
339
low pH like juices, and does not resist to prolonged heat and pasteurization procedures, thus
340
having very high stability, even higher then saccharin and acesulfame K. It has a pleasant
341
taste without sourness or metallic residue (usual in some types of sweeteners) and a
342
sweetening capacity of 180 to 200 times sucrose. It is however, considered a source of
343
phenylalanine thus not being advised for people with phenylketonuria (Shankar et al.,
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2013). Furthermore, there are reports of toxicity and hepatocellular alteration in long-term
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exposure to it (Abhilash et al., 2011). According to regulation of the EU No. 1169/2011, all
346
food that uses aspartame has to have a visible section containing “contains aspartame
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(source of phenylalanine)”. Its ADI is 40 mg kg-1 of body weight. Further recommendations
348
should be considered, given that the use of aspartame in food with a pH higher than 6 can
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make it transform into diketopiperazine, a carcinogenic compound (Rycerz and Jaworska-
350
Adamu, 2013). Aspartame is used in refreshments, yogurts, lactic beverages, desserts,
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baked goods and others (Mitchell, 2006; Nabors (Part I), 2001; O’Donnell and Kearsley,
352
2012). It has always been a target of intense studies regarding its safety, although being
353
widely regarded as safe, this sweetener has seen recent studies, (2010 and onwards)
354
pointing outs its nephrotoxicity, hepatotoxicity, damage to nerves, cancer, and even type 2
355
diabetes (which is strange given the non-nutritional nature), being all these diseases
356
reported in murine models (Ashok et al., 2013; Fagherazzi et al., 2013; Haliem and
357
Mohamed, 2011; Okasha, 2016 Saleh, 2014; Soffritti et al., 2010). Despite having evident
358
differences, the human body and metabolism shares some similarities with these models,
359
which perpetuates the mistrust of this molecule by the public. Inversely, a review published
360
in the Food and Chemical Toxicology Journal, authored by Kirkland and Gatehouse in
361
2015, deems aspartame safe, after reviewing all available data from various sources. The
362
authors state no toxicity in gene mutations, some evidence of chromosomal damage in
363
vitro, while bone marrow micronucleus, chromosomal aberration and comet assays found
364
no toxicity in somatic cells, supporting the claim by the EFSA of a non-genotoxic
365
compound. In 2014, an article signed by Suez et al. and published in Nature referred to
366
aspartame as inducing glucose intolerance by altering gut microbiota, requesting that a
367
reassessment of non-caloric artificial sweeteners be carried out. Concomitantly, PepsiCo
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announced in 2015 that they would remove aspartame from their diet version of the famous
369
drink, bowing to consumer demand of an aspartame free drink. In 2016, after a crash in
370
sales, PepsiCo reintroduced aspartame in their beverage, claiming that some consumers
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found a difference in taste, making the company produce three types of beverage: the
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original Pepsi, one with aspartame and one with a natural sweetener to meet all customer
373
demands. This small industrial maneuver further deepens the plot and casts more distrust
374
and fear in customers, which are left baffled without actually knowing if aspartame is safe
375
or not (CNBC, 2015, 2016;Paolini et al., 2016). A
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Figure 12. Chemical structure of the amino acids L-phenylalanine (A), L-aspartic acid (B),
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which are the building blocks of aspartame (C).
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Cyclamates (E952), discovered in 1937 at the University of Illinois, are a very good
382
example of the legislative discrepancies between the EU and USA. The European Union
383
has approved its use in food, while the FDA removed its GRAS status in 1969 and
384
completely banned it in 1970. It is now pending approval for re-admission. The base for
385
this ban is a study that relates the metabolization of cyclamates to cyclohexylamine (toxic
386
compound), and although a later study pointed out that this metabolization only takes place
387
in a small amount of the population, it has not been enough for the FDA to remove the ban.
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Its industrial production could be the reason for this intransigent maneuver, given that it is
389
obtained though the sulfonation of cyclohexylamine (Renwick and Nordmann, 2007).
390
China, Indonesia, Taiwan and Spain are the biggest producers of this sweetener, which,
391
along with saccharin are the least expensive to produce (Nabors (Part I), 2001). In the EU,
392
the ADI is set at 11 mg Kg-1 of body weight and is used in desserts, baked and processed
393
food, soft drinks, canned fruits, gelatins and as tabletop sweeteners (Carocho et al., 2014).
394
One of the drawbacks of cylamates is the slight sour taste, although its sweetening capacity
395
is set between 35 to 50 times stronger than sucrose. The long-lasting sweetness if put off by
396
a sour aftertaste, so it is almost always combined with saccharin (Martins et al., 2010;
397
Mitchell, 2006O’Donnel and Kearsley, 2012; Renwick et al., 2004; Roberts, 2016;
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Takayama et al., 2000).
399
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Figure 13. Chemical structures of the precursor cyclohexylamine (A) and sodium
401
cyclamate (cyclamate) (B).
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Saccharin (E954) was the first discovered intense sweetener, back in 1878. Today, more
404
than 100 years later, it is produced at an industrial scale, though a process called Maumee,
405
which derives from the company that developed the technique (Maumee Chemical
406
Company). In this process, phathalic anhydride is converted to anthranilic acid to then react
407
with nitrous oxide, nitrogen dioxide, chlorine and ammonia, forming saccharin Carocho et
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al., 2014 Mitchell, 2006. This compound is stable at low pH and resists high temperatures,
409
which makes it an ideal sweetener to be used in production steps of foods and for long
410
lasting goods. It has a sweet taste, but also a slight acid contamination so it is combined
411
with cyclamates and aspartame. It can have 300 times the potency of sucrose in terms of
412
sweetening, but has the lowest ADI of all non-caloric sweeteners, only 5 mg Kg-1 of body
413
weight. In terms of consumption, it has always been controversial, with Canada banning its
414
use in 1977 after animal testing showed toxicity. In that same year, the US considered
415
doing the same, but Congress placed a moratorium on this decision, having other studies
416
then ruled out the adverse effects. All these studies were based on the formation of tumors
417
in rats, namely in the bladder (Nabors (Part I), 2001). Thus, given the anatomical
418
differences between mouse and man, the danger for humans was ruled out. Today,
419
numerous studies have deemed saccharin safe and its consumption is, today, safe, fostering
420
the increase of its use all over the world (Shankar et al., 2013). As like acesulfame K,
421
saccharin is excreted through urine and is not metabolized in the body, although it can cross
422
the placenta of pregnant woman and can be transferred through breast milk, thus not being
423
recommended to pregnant women or breastfeeding ones. It is employed in fruit juices,
424
processed fruit, gelatins, marmalades, coverings, sauces, desserts, bubble gum and tabletop
425
sweetener (Swither et al., 2013; Takayama et al., 1998; Whysner & Williams, 1996).
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Neotame (E961) is a sweetener with a very similar structure to aspartame, in fact, they are
428
isomers, but neotame has a very high sweetening power, from 7000 to 13000 times stronger
429
than sucrose and less than 1.2 kJ g-1 Mayhew et al., 2003. It has a clean taste, with no
430
metallic or acid aftertaste. Like sucralose, it was only discovered in the 80’s and is obtained
431
by reductive alkylation of aspartame, which is converted into 3,3-dimethylbutyraldehyde.
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Given the lack of phenylalanine in its composition, it is safe for phenylketonuria patients,
433
but also safe for diabetics O’Donnell and Kearsley, 2012. It is used mainly in synergies
434
with other sweeteners (except acesulfame-k and saccharin) and for soft and lactic drinks,
435
sauces, yogurts, lemon tea, as tabletop and in bubble gum, but also as an enhancer of
436
natural flavors, namely acidic fruit flavors. It is stable under dry storage conditions, not
437
hygroscopic and appears a white crystalline odorless powder. In terms of metabolization,
438
half of the ingested neotame is not absorbed and excreted through the feces while the other
439
half in excreted in the urine as de-esterified neotame. It meets the five basic criteria for
440
commercial viability of a nonnutritive sweetener: taste, solubility, stability, safety and cost.
441
Regarding safety, neotame, as has been subject to a battery of tests, in which, even at doses
442
higher that its ADI, no toxicity was detected. No adverse findings were reported for
443
physical examinations, water consumption, clinical pathology evaluations, no reports of
444
morbidity, mortality, organ toxicity, macroscopic or microscopic postmortem findings in
445
murine models and other test animals (Mitchell, 2006; Nabors (Part I), 2001; Nofre and
446
Tinti, 2000; Zhu et al., 2016).
SC
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EP
447
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432
Advantame (E969) is one of the newest sweeteners to be approved in the EU, in 2013. It is
449
obtained through chemical synthesis from aspartame and isovaniline. Contrary to neotame,
450
advantame is a source of phenylalanine, and even though it is derived from aspartame, it
451
has a very different structure. The sweetening power of this molecule is around 20,000
452
times the one of sucrose and it appears a white to yellow powder (Warrington et al., 2011).
453
It has a very sweet flavor with little intensity of bitter and sour. It has been successfully
454
used in coffee, iced tea, powdered beverage formulations, chewing gum, yogurt, and also as
455
a flavor enhancer (Otabe et al., 2011a). In terms of stability, it can withstand high
AC C
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temperatures and be used in low pH products.
In July 2013, EFSA experts defined
457
advantame as non-toxic or carcinogenic and there are no risks of its consumption as a food
458
additive. The ADI was established at 5 mg kg-1 of body weight per day. Model animal (rats,
459
dogs) and human trial data suggest that there are no issues with the use of advantame as a
460
food sweetener (EFSA, 2013; Otabe et al., 2011b; 2011c; 2011d; Ubukata et al., 2011).
RI PT
456
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A
461 462
AC C
463
EP
TE D
B
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SC
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C
464
Figure 14. Chemical formulas of A – saccharine, B – neotame, and C – advantame.
M AN U
465 466
Sucralose (E955) is another intense synthetic sweetener, obtained industrially by
468
substitution of the three hydroxyl groups in sucrose Roberts et al., 2008. This
469
transformation renders this molecule 750 times sweeter than the precursor, sucrose. Its ADI
470
is 5 mg kg-1 of body weight (as saccharin), although sucralose suffers metabolization in the
471
human body. This metabolization is related to migraines, intestinal unrest and inhibition of
472
colonic bacteria when consumed in high amounts. The principal applications of sucralose
473
are yogurts, ice cream, canned fruits, biscuits, caramels, soft drinks, lactic products, baked
474
goods, gelatins, marmalades, bubble gum, among others Mitchell, 2006; Nabors (Part I),
475
2001; O’Donnell and Kearsley. Despite some research pointing out the possible connection
476
of the consumption of sucralose with cancer at the beginning of the century, a review article
477
authored by Berry et al. (2016), stressed that there is no relation, even at higher dosages
478
that the previewed in the ADI. Furthermore, back in 2009, another review article that
479
thoroughly reviewed all the available studies at the time pointed out that there are no risks
480
in consuming this additive, and many studies in vivo, in vitro and with human trials point
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out the overall safety of sucralose Grotz and Munro, 2009; In 2012, another paper refuted
482
claims of previous ones that questioned the safety of sucralose, namely in stability in vivo,
483
chemical reactivity of sucralose, stability at high temperatures and interaction with
484
cytochrome P450 Shiffman and Abou-Donia, 2012. Recently, more controversy shattered
485
the public opinion, when in 2016 an article pointed out that consumption of sucralose
486
increases food intake through a neuronal fasting response Wang et al., 2016. The research
487
was carried out in Drosophila flies for their simple genome and fast replicating speeds.
488
Recently, in the same journal, Cell Metabolism, a new research implies the contrary, stating
489
that sucralose suppresses food intake, using the same test subjects. Another study, dated
490
2017 claimed that children, due to their lower weight and blood volume, have a higher
491
amount of sucralose in circulation, and that measures should be taken to determine the
492
security of this occurrence Sylvetsky et al., 2017; Park et al., 2017. These conflicting
493
results just bring more doubt towards the consumption of sucralose. A
B
495 496
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494
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481
Figure 15. Molecular structure of sucrose (A) the precursor of the sweetener sucralose (B).
497 498
Table 3. Structure, ADI and sweetening power of the most common synthetic intense
499
sweeteners. Data extracted from Mitchell, 2006; Otabe, 2011c; Varzakas et al., 2012.
ACCEPTED MANUSCRIPT
ADI (mg/kg/day)
Brand Names
Sweetening power
Advantame - E 969
5
-
37000
Neotame - E 961
2
Newtame®
7000-13000
Sucralose – E955
5
Splenda®
400-800
RI PT
Name
Sweet and Low® Saccharin - E 954
5
Sweet Twin®
240-300
SC
Sweet N’Low® Nutrasweet® 40
Equal®
M AN U
Aspartame - E 951
200
Sugar Twin® Sweet One®
Acesulfame K - E950
9
150-200
Sunett®
EP
TE D
Assugrin®
AC C
Cyclamates - E 952
Chuker® Cologran® Hermesetas® Huxol®
11
Novasweet® Rio® Sucaryl® Sugar Twin® Suitli® Sweet N’Low®
500
30-80
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4.2. Natural intensive sweeteners
502
In recent years, the use of natural sweeteners has been increasing, mainly due to demand
503
from consumers. Even though natural organisms like the EFSA or FDA do not differentiate
504
sweeteners by synthetic or natural, being all sweeteners regulated by the EU normative
505
1129/2011.
RI PT
501
The most common natural sweeteners are steviol glycosides (E960), thaumatin
507
(E957) and neohesperidine dihydrochalcone (E959). Others, like tagatose and glycyrrhizin
508
also exist in the market but are not allowed to be used within the EU (Table 5).
SC
506
Steviol glycosides (E960) are molecules extracted from the leaves of Stevia
510
rebaudiana Bertoni, a plant from the Asteraeae family that is native from Paraguay and
511
Portugal. The plant has such a high concentration of steviosides that it can be directly used
512
as a sweetener (Lobete et al., 2017). The leaves are not allowed to be used in the EU, but
513
the purified, steviol glycosides compounds, are (Periche et al., 2015). They are extracted
514
with hot water and then recrystallized in a hydroalcoholic solution. Steviol glycosides
515
consist of mixtures of different compounds, namely stevioside (5-10%), rebaudioside A (2-
516
5%), rebaudioside C (1%), dulcoside A (0.5%), rebaudioside D, E and F (0.2%). Among
517
them, the sweetest compound is rebaudioside A (Gonzales et al., 2014; Momtazi-Borojeni
518
et al., 2016). The combination of these molecules has a sweetening power of over 300 times
519
sucrose and an ADI limit of 4 mg kg-1 of body weight per day. These molecules are
520
metabolized by the colonic bacteria, converting them to steviol glucoronides to finally be
521
excreted through urine. In terms of caloric contribution, it is neglectable, a thus safe for
522
diabetic patients, while properties like anti-inflammatory and diuretic effects are also
523
attributed to the compounds that comprise the mixture. Furthermore, it is relatively stable to
524
heat, can operate at a pH of 2 to 10. It displays a clean sweetness, although some of the
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509
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components have a bitter taste. A small slice of the research concerning this sweetener has
526
shown concern about toxicity and genotoxicity of these compounds, although many authors
527
claim the database of in vitro and in vivo studies is robust and there is no indication of the
528
toxicity of stevioside and rebaudioside (Barriocanal et al., 2008; Brusick, 2008; Wheeler et
529
al., 2008). Recently, concerns about the endocrine disruption potential of steviol glucosides
530
has become a hot topic, with publications claiming there is a potential risk of these
531
compounds to have disrupting effects, suggesting further and deeper research on this
532
subject (Shannon et al., 2016; Urban et al., 2013, 2015). The uses of stevia encompass ice
533
creams, yogurts, cakes, sauces, drinks, bread, pastry, flavored milk, spices and as a tabletop
534
sweetener (Baines and Seal, 2012; Brandle et al., 2008; Carocho et al., 2015; Nabors (Part
535
I), 2001; Prakash and Chaturvedula, 2016).
M AN U
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525
A
OH
OH
OH
O
OH
O
O
TE D
O
OH
OH
EP
H3C
H
O
536
O
AC C
OH OH
OH
O
H CH3
OH OH
CH2
ACCEPTED MANUSCRIPT
M AN U
SC
RI PT
B
AC C
EP
C
TE D
537
538
ACCEPTED MANUSCRIPT
M AN U
SC
RI PT
D
539 540
Figure 16. The most representative compounds of steviol glycosides, namely stevioside
541
(A), rebaudioside A (B), rebaudiocide C (C), and dulcoside A (D).
542
Thaumatin (E957) is also a mixture of compounds, namely proteins, which are extracted
544
from the Thaumatococcus danielli Bennett plant, which is endemic to Africa (Baines and
545
Seal, 2012). It is a single-chain of 207 amino acid residues, which provide a sweet taste at
546
concentrations as low as 50 nM. There are other examples of sweet proteins, like monellin,
547
brazzein, and lysozyme, but thaumatin is the most widespread example of protein-based
548
sweeteners (Beauchamp, 2016; Firsov et al., 2016). The extraction is carried out with water
549
and mechanical processes, being the most important compounds Thaumatin A and B. In the
550
plant, these proteins display antimicrobial and protective functions, as sweeteners, they can
551
be 2,000 to 3,000 times stronger than sucrose, although the sweetness is quite slow to
552
develop and has a residual taste of licorice, thus being used in combination with other sugar
553
substitutes. In terms of stability, it has a high resistance to heat and acidic pH, while being
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543
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very soluble in water. Furthermore, it has no caloric contribution and is very soluble in
555
water and stable at high temperatures (Baines and Seal, 2012; Pawar et al, 2013). It also has
556
a use as a flavor enhancer at a maximum of 0.5 mg kg-1, being used in food commodities
557
and supplements (EFSA, 2015). As a sweetener, it is approved both in the EU (since 1984)
558
and the US, where it is considered GRAS. Soups, sauces, processed vegetables and egg-
559
derived products are the main foods where it is used. Given the instabilities of its endemic
560
region in West Africa, and climate change, the production of thaumatin is not enough for
561
demand, therefore, many studies have focused on the production of recombinant thaumatin
562
through microorganisms and transgenic plants (Jain and Grover, 2015; Masuda, 2016;
563
Nabors (Part I), 2001).
566
SC
M AN U
TE D EP
565
Figure 17. Representation of the protein thaumatin created with PYMOL software.
AC C
564
RI PT
554
567
Neohesperidin dihydrochalcone (E959) is another intense semi-natural sweetener that
568
comes from the skin of the immature fruits of Citrus aurantium L. When extracted, this
569
compound is a flavone, neohesperidin, which after suffering hydrolysis becomes a
570
dihydrochalcone (Baines and Seal, 2012). Other method to obtain neohesperidin
571
dihydrochalcone is through synthesis of naringenin, extracted from the fruit of Citrus
572
paradise Macfad. This sweetener is reasonably hygroscopic and is stable at high
ACCEPTED MANUSCRIPT
temperatures, namely during pasteurization, but quite insoluble, and presents an off-white
574
crystalline powder, although being poorly soluble in water at room temperature but highly
575
soluble in hot water (Nabors (Part I), 2001). This fact is attenuated by the low quantities
576
needed in food, and the fact that it is used in combination with polyols or glucose syrup. Its
577
sweetening power, although quite high is far from the most potent ones, achieving only
578
1,500 times stronger than glucose, and also has a very slow sweetening speed and a
579
menthol residue. One of its functions when used with other sweeteners is to mask their
580
unwanted tastes. It has a high ADI, of 35 mg kg-1 of body weight per day and does not
581
accumulate in tissues given to its quick metabolization and excretion (EFSA, 2011).
582
Approved in the EU since 1994 but not in the US. This natural sweetener is also used to
583
thicken liquid foods, so it is used for ice creams, bubble gums, pastry, water-based flavored
584
drinks, milk and derivatives, snacks, confectionary foodstuffs, beer, soups, food
585
supplements and as a tabletop sweetener and fruit derived food (El-Samragy; Spillane,
586
2006).
587 588 589
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573
Figure 18. Chemical structure of neohesperidin dihydrochalcone.
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Glycyrrhizin, or more correctly glycyrrhizinic acid is a triterpenoid saponin that is obtained
591
from the roots and rhizome of Glycyrrhiza glabra, a plant known as licorice. It is described
592
as being from 30 to 200 times sweeter than sucrose. Apart from this, it is also recognized
593
for having several pharmacological and biological activities, namely anticancer, anti-
594
inflammatory, hepatoprotective, antioxidant and antiviral. In the US, glycyrrhizin is
595
considered GRAS although there is a guideline for the maximum permitted levels for the
596
saponins on several preparations (Karkanis et al., 2016). In the EU, although the
597
Commission Report states that the consumption is safe, a limit of 100 mg per day is
598
recommended, given the glucocorticoid effects id the glycyrrhetinic acid present in the
599
extract. Still, given that the use of this extract is not widespread, these levels are related to
600
the consumption as licorice rather than a sweetener (Komes et al., 2015). One drawbacks of
601
using glycyrrhizin is the potential hypertensive effects. Still, it has been used previously in
602
candies, chewing gum, toothpaste, beverages and tobacco. Furthermore, its specific aroma
603
and intense aftertaste are reasons that it has not been very widespread (Graebin, 2016;
604
Omar et al., 2012).
SC
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EP AC C
605
RI PT
590
ACCEPTED MANUSCRIPT
O HO
H OH
RI PT
O
O
O OH H O OH
O H
O
SC
O
HO OH
OH
607
OH
M AN U
606
Figure 19. Representation of glycyrrhizin.
608
Tagatose is a ketohexose that is structurally similar to lactose, displaying a hydroxyl
610
group in C4, and can be found in small quantities in fruits (cacao) and in dairy products. It
611
is obtained from lactose, though an enzymatic process followed by an isomerization and
612
purification steps. It displays a staggering 92% of sweetness potency, but with only one
613
third of the calories, making it interesting for sweetening food (Bell, 2016; Jayamuthunagai
614
et al., 2016). Even though it is considered a sugar, it does not promote tooth decay.
615
Furthermore, tagatose, by having a different metabolization to sucrose, does not interfere
616
with blood glucose levels, deeming it safe for diabetic individuals. Of all the consumed
617
tagatose, only 20% is absorbed by the intestine and readily excreted in urine (Ensor et al.,
618
2014; Lu et al., 2007; Tandel, 2011; Levin, 2002). Although tagatose is naturally occurring,
619
its production is now industrialized (through enzymatic reactions), making its classification
620
as a semi-synthetic compound in foodstuffs, and rendering a colorless crystalline powder
621
with a bitter aftertaste, but compatible with a wide range of food ingredients It has
AC C
EP
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609
ACCEPTED MANUSCRIPT
considerable advantage when compared to other natural and synthetic sweeteners since it
623
can be considered a prebiotic and has a similar taste to sucrose (Dobbs and Bell, 2010; Oh,
624
2007). It is stable at pH 2 − 7, displays a high solubility in water, making it ideal to also be
625
used as a flavor enhancer, although it lacks some stability. Furthermore, it shows humectant
626
behavior like sorbitol, but decomposes faster than sucrose at high temperatures. Tagatose is
627
approved in New Zealand, Korea and in the EU, although its use in the EU is not as a
628
sweetener, rather as a food ingredient. In the USA, it is considered GRAS and can be used
629
as a low-calorie sweetener. Its applications encompass beverages, cereals, bubble gum,
630
chocolate, caramels yogurts, ice creams, nutritional supplements, and candy. Some
631
conflicting results have been found regarding its effects on gastrointestinal unrest.
632
Genotoxic studies have been carried out and determined tagatose as non-genotoxic (Baines
633
and Seal, 2012; Kim, 2004; Nabors (Part I), 2001).
M AN U
SC
RI PT
622
B
635 636 637 638
AC C
634
EP
TE D
A
Figure 20. Lactose and tagatose
ACCEPTED MANUSCRIPT
639
Table 5. Natural intense sweeteners, ADI, structure and sweetening power ADI (mg/kg/day)
Brand Names
Sweetening power
Thaumatin - E957
50
-
2000
Neohesperidine dihydrochalcone – E959
35
-
1500
RI PT
Name
Truvia®
Steviol glucosides - E960
4
PureVia®
300
Glycyrrhizin
Not specified
SC
Enliten®
M AN U
Not considered a food Tagatose
-
100
-
0.92
additive
640 641
5. Conclusions and Future perspectives
The WHO directives state that sugar should not represent more than 10% of the
643
daily caloric contribution, and is preparing to propose a reduction to 5% in the near future
644
(Mooradian et al., 2017). This is a huge burden and at the same time an opportunity for the
645
food industry, governments and consumers! For one, the opportunity to reduce the
646
consumption of sugar is beneficial, lowering the health issues associated with its excess
647
consumption, translating in a reduction of health spending by governments. On the other
648
hand, stronger and more effective sweeteners are necessary to be added to food to carry out
649
sweetening functions without increasing the quantity of added sweetener, due to legal
650
restrictions and the alleged health implications of sweeteners.
AC C
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642
651
The recent discovery that non-caloric sweeteners also seem to increase the
652
prevalence of diabetes and weight, unravels a grim future for patients with sugar
653
restrictions and the average consumer, whom cannot be free from the dangers of eating? Or
ACCEPTED MANUSCRIPT
is research “simply just seeking to deep?” Is research trying to find, at all costs, culprits for
655
sicknesses, and links between sweeteners and illnesses? (Fowler et al., 2008; Imamura et
656
al., 2015; Koning et al., 2011) Could some of these metabolic disorders happen to be, like
657
cancer, which recent studies state that two thirds of carcinomas are a matter of “luck” rather
658
than lifestyle or gene disorders? What will be the fate of eating in the beginning of the
659
century? (Nowak and Waclaw, 2017; Tomasetti and Vogelstein, 2015).
RI PT
654
Further entropy arises when similar studies end up in conflicting results. One
661
incredible example is detailed by Bes-Rastrollo et al. (2013), in which similar studies found
662
contradicting results. In one, funded by food industry companies, in 83% of studies stated
663
that insufficient proof was detected for a correlation among the consumption of sugar-
664
sweetened beverages and weight gain, while in other studies, without industrial financing,
665
the same percentage could relate the increase in weight with the consumption of such
666
beverages.
667
researcher, especially clinical investigators when carrying out their research while being
668
funded by enterprises. The risk of biased reports in the food industry is continuous, given
669
the different ways associations of enterprises and researchers can be achieved, namely
670
through sponsorships of journals and conferences, sponsorships of research studies,
671
partnerships and alliances. Although there is always a latent risk in virtually all areas,
672
because advances in industry come from research, tight regulation is critical to avoid these
673
types of occurrences that just discredit both the industry and research (Boyd et al., 2003;
674
Nestle, 2001).
M AN U
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660
AC C
EP
TE D
Even before this study, uncomfortable positions have been identified by
675
After a “not so peaceful” coexistence between consumers and sweeteners, fueled by
676
scandals, legislation gaps and controversies, and occasional deception by the industry, the
677
public wants to be assured that they are consuming safe sweeteners. There are many forms
ACCEPTED MANUSCRIPT
to induce trust in consumers, but they rely on combined efforts from the industry,
679
governments, press/media and consumers. The industry must, at all costs research and
680
produce safe, sound, cheap, easily producible, sustainable and strong sweeteners.
681
Governments must act in two manners. Firstly, combining efforts to avoid legislation gaps
682
and harmonizing legislation across the many governing bodies (EFSA, FDA…), which can
683
be an incredible leap in gaining consumer trust. In the XXI century, it is unthinkable that
684
cyclamates and neohesperidine dihydrochalcone are allowed in the EU and not in the US,
685
while D-tagatose is not considered a sweetener in the EU and cannot be used as one, if the
686
scientific background is available for both governing bodies to consult and legislate
687
accordingly. Why the legislation difference? The second effort that could be put forward by
688
governments is the public education regarding eating, healthy lifestyles and choices. The
689
press and media play a role in the scandals, speculation and exaggeration of studies and
690
legislation, and should tone down when disseminating information that can be badly
691
interpreted by the public, especially the uninformed fringe. Finally, the consumer must, at
692
all costs seek trustworthy information to make informed decisions about what they are
693
eating. In the era where information is everywhere, finding reliable information can be the
694
difficulty, but scientific publications are somewhat easier to find as they tend to become
695
open source. Reading the article or study that originated a news article is always better than
696
to read the news itself, for the scientific reports are stripped from exaggeration and
697
extrapolation, conveying specific findings.
SC
M AN U
TE D
EP
AC C
698
RI PT
678
What are the next generation of sweeteners, and how are they going to affect the
699
population is the question to be asked. There should be a constant seek for new low caloric
700
sweeteners, namely isomers of known ones and other related compounds that have should
701
have higher sweetening powers, lower production costs, lower caloric contribution and no
ACCEPTED MANUSCRIPT
health impact. Concomitantly, the major investment should be on both synthetic and natural
703
non-caloric sweetener. The synthetic molecules will be rearrangements of known
704
sweeteners or prospection for new ones, relying on combinatorial chemistry, but also the
705
improvement of the production of widespread sweeteners. The answer to passing the idea
706
of safety could be the production of these compounds through ecological and sustainable
707
processes, translating in a better understanding of the public, while associating sweeteners
708
with eco-friendly and safety ideas. The marketing of studies that deem artificial sweeteners
709
safe is critical to, through scientific discovery inform consumers that they are consuming
710
safe chemicals. The natural sweeteners financing will be for better extraction methods of
711
currently impracticable compounds and the discovery of new sources of sweetening
712
molecules. Natural sweeteners have been becoming more widespread due to the public’s
713
perception that what is natural is less hazardous for health, and both manufactures and food
714
companies have started to shift considerable amounts of funds to new natural sweeteners.
TE D
M AN U
SC
RI PT
702
Further innovations in the sector could arise from new types of sweeteners or
716
improvements. Compounds like miraculin, which is not a sweet molecule, but alters taste
717
buds to perceive food as sweet could be improved while, other similar molecules can be
718
found in nature or synthesized and used in the food industry. These molecules or extracts
719
could be added to food to make it be perceived as sweet, rather than making them actually
720
sweet, ultimately avoiding alleged health impacts from sweeteners.
AC C
721
EP
715
Although some improvements and innovations may seem temporally closer than
722
others, the truth is that the sweeteners market, mainly regarding sweeteners as food
723
additives, will be suffering changes and having to tackle health and economic issues, while
724
coping with regulation that should become more harmonic to ensure trust and peace of
725
mind for consumers, because the reduction of sugar intake seems imminent and necessary.
ACCEPTED MANUSCRIPT
By 2020, EFSA will be providing scientific advice of added sugar in food, establishing a
727
science-based cut-off value for daily exposure to added sugars from all sources which is not
728
associated with adverse health effects. This means that the concerns about sugar’s effects
729
on health are real, making this an opportunity for the sugar substitutes to become safer,
730
trustworthy, and, expectedly sweeter.
RI PT
726
731
Acknowledgments
733
The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) and
734
FEDER under Programme PT2020 for financial support to CIMO (UID/AGR/00690/2013).
735
Author
736
SFRH/BPD/114650/2016.
Márcio
Carocho
also
737
M AN U
SC
732
thanks
FCT
for
his
Conflict of Interest
739
The authors state no conflicts of interest regarding the manuscript.
740
grant
TE D
738
post-doctoral
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742
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743
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741
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Aidoo, R.P., Depypere, F., Afoakwa, E.O., Dewettinck, K. 2013. Industrial manufacture of
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751
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754
Baines, D., y Seal., R. 2012. Natural food additives, ingredients and flavourings, Woodhead Publishing Limited, Cambridge, UK.
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ACCEPTED MANUSCRIPT HIGHLIGHTS Sweeteners are essential to reduce caloric intake in diets Some sweeteners are still seen with distrust by consumers Natural sweeteners are gaining interest from consumers and companies There are still some legislation discrepancies among the EFSA and FDA concerning sweeteners
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