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A comparative FTIR study for supplemented agavin as functional food
Journal Pre-proof A comparative FTIR study for supplemented agavin as functional food Oscar F. Vázquez-Vuelvas, Félix A. Chávez-Camacho, Jorge A. Meza-Velázquez, Emilio Mendez-Merino, Merab M. Ríos-Licea, Juan Carlos Contreras-Esquivel PII:
S0268-005X(18)31730-2
DOI:
https://doi.org/10.1016/j.foodhyd.2020.105642
Reference:
FOOHYD 105642
To appear in:
Food Hydrocolloids
Received Date: 3 September 2018 Revised Date:
3 January 2020
Accepted Date: 3 January 2020
Please cite this article as: Vázquez-Vuelvas, O.F., Chávez-Camacho, Fé.A., Meza-Velázquez, J.A., Mendez-Merino, E., Ríos-Licea, M.M., Contreras-Esquivel, J.C., A comparative FTIR study for supplemented agavin as functional food, Food Hydrocolloids (2020), doi: https://doi.org/10.1016/ j.foodhyd.2020.105642. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2020 Published by Elsevier Ltd.
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A comparative FTIR study for supplemented agavin as functional food
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Oscar F. Vázquez-Vuelvas,a,* Félix A. Chávez-Camacho,b Jorge A. Meza-Velázquez,c Emilio Mendez-
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Merino,d Merab M. Ríos-Licea,d Juan Carlos Contreras-Esquivel.b, e, *
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a
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de Colima, Km 9 Carr. Colima-Coquimatlan s/n. Coquimatlan, Colima. C. P. 28400, Mexico.
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b
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Universidad Autónoma de Coahuila. Saltillo, Coahuila. 25280. México.
Laboratory of Biochemical Engineering and Bioprocesses, Faculty of Chemical Sciencies, Universidad
Laboratory of Applied Glycobiotechnology, Food Research Department, School of Chemistry,
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c
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Palacio, Durango. C. P. 35010, Mexico.
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d
Sigma Alimentos Co., Torre Sigma, San Pedro Garza Garcia, Nuevo Leon. C. P. 66260, Mexico.
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e
Research and Development Center, Coyotefoods Biopolymer and Biotechnology Co., Simon Bolivar
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851-A, Saltillo, Coahuila. C. P. 25000. Mexico.
Food Science Laboratory, School of Chemistry, Universidad Juarez del Estado de Durango, Gomez
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Corresponding authors:
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[email protected]
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[email protected]
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* These authors contributed equally to this work.
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Abstract
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Functional foods are products focused to human consumption with benefits to different physiologic
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aspects in order to prevent diverse metabolic problems in the body. Prebiotics recently have been started
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to be employed as functional foods, and fructans as inulin or agave inulin, known as agavin, represent a
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valuable source of them. Standard polysaccharides as starch, inulin, cellulose and agavin were
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vibrationally analyzed by FTIR spectroscopy, as well as solid mixtures with different agavin-cellulose
40
and agavin-cocoa ratios, to identify important absorption peaks to detect evolutive changes of bands in
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absorbance intensities and wavenumbers displacements, in order to employ this information for possible
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adulteration in this prebiotic functional foods. Three commercial products identified as supplemented
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agavins with Aloe vera, antioxidants and cocoa were vibrationally analyzed and described by
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comparative visualization with standard solid mixtures for detecting discrepancies with ingredient
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compositions. The vibrational patterns displayed by standard polysaccharides allowed to identify
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frequency zones for making an approach to elucidate standards; furthermore, solid mixtures of standards
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described the evolution of absorption peaks proportionally to the ratio of the samples. Spectra of agavin-
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cellulose and agavin-cocoa solid mixtures exhibited an increment in bands associated with C-O and C-
49
O-C between 1176 cm-1 and 1074 cm-1 when the agavin content diminished in the mixture; an opposite
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behavior was depicted at 926 cm-1 absorption band, intensity
51
decreased. The spectra of commercial agavins provided the information to identify structural similarities
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with the absorption bands shown by polysaccharide standards, which made it possible to identify the
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presence of the components of interest.
54 55 56 57 58 59 60 61 62
Keywords: FTIR, fructan, agavin, polysaccharide, functional food
decreased when the agavin ratio
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1. Introduction
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Functional foods represent a series of food products with benefits to diverse physiological aspects for
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humans (Konar et al., 2018). Functional foods may be described as nutriments that affect positively to
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different targets in the body to promote health (Donato-Capel et al., 2014), by cure and/or prevention of
68
diverse
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functional food characteristics associate with a recent definition of prebiotic concept, since they are
70
substrates that are selectively utilized by gastrointestinal microorganisms to confer health benefit to the
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host (Konar et al., 2018).
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The elaboration of functional foods requires supplements with a high nutritional value, since they have
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been gaining interest, an increment in their value has occurred; as a consequence, functional foods have
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become economically valuable (Oreopoulou & Tzia, 2007). In this sense, hydrocolloids are widely used
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to produce functional foods and are catalogued as fibre-rich foods or dietary fiber; they are defined as
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any carbohydrate that does not hydrolyze in the gastrointestinal tract. Nevertheless, a more complete
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definition is about those carbohydrate polymers with ten or more monomeric units, which are not
78
hydrolyzed by endogenous enzymes in the small intestine of humans (Perry & Ying, 2016).
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Fructans are a group of soluble polymeric carbohydrates considered as dietary fiber according to
80
structural, analytical and physiological concepts (Handa, Goomer, & Siddhu, 2012). They are
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constituted basically by fructose units; and after starch, fructans are the most abundant non-structural
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polysaccharides (Mancilla-Margalli, López, & López, 2006; Muñoz-Gutiérrez, Rodríguez-Alegría, &
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López Munguía, 2009; Velázquez-Martínez et al., 2014). From the structural point of view, fructans are
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macromolecules naturally synthetized from sucrose and named considering the linkage type present in
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the carbohydrate chain. Inulins are fructans with the predominant β(2-1) fructosydic bond, and levans
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when the main fructosydic linkage is β(2-6), both linked to the fructosyl unit of saccharose (Muñoz-
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Gutiérrez et al., 2009). In addition, fructans obtained from Agave tequilana plants are known as agavins
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and are considered a series with a highly branched chains defined by linked fructosyl units with a
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combination of β(2-1) and β(2-6) fructosydic bonds (Mancilla-Margalli et al., 2006; Muñoz-Gutiérrez et
90
al., 2009; Waleckx, Gschaedler, Colonna-Ceccaldi, & Monsan, 2008). The fructan biopolymer presents
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different degree of polymerization; the number of linked fructosyl residues may vary from 2 to 60
metabolic disorders or illnesses (Dubey, Toh, & Yeh, 2018; Konar et al., 2018). These
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residual units, and comparatively to sucrose, they are 10% as sweet as sucrose, an attractive organoleptic
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property that enhances palatability of fructans as a functional food ingredient. Oligomer molecules are
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constituted by no more than ten fructofuranosyl units, and are better known as fructooligosaccharides
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(FOS) or oligofructose (Apolinário et al., 2014; Brownlee, 2011; Franck, 2006; Mensink, Frijlink, Van
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Der Voort Maarschalk, & Hinrichs, 2015).
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In Mexico, the agave species represent an appreciated bioresource due to several of them are
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economically important for producing a wide variety of distilled and fermented beverages (Ávila-
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Fernández, Galicia-Lagunas, Rodríguez-Alegría, Olvera, & López-Munguía, 2011). Agave tequilana,
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raw material to produce Tequila, is mainly harvested to this purpose (Montañez-Soto, Venegas-
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gonzález, Vivar-Vera, & Ramos-Ramirez, 2011); however, agave fructans have recently become
102
attractive ingredients because of its characteristic as dietary fiber and prebiotic activity. Numerous
103
reports indicate that consumption of specific hydrocolloids as fructans may regulate the composition of
104
the intestinal flora, to promote the production of biologically short chain fatty acids in the human large
105
bowel, especially the butyric acid, which has important anticarcinogenic effects (Li & Nie, 2016).
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The agave inulin (agavin) recently started to be commercially available in Mexico as a supplement; this
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makes agavin powder become valuable as a food supplement from the economical point of view, due to
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the value as a dietary fiber source and sweetener. Consequently, agavin powder may be a target of
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adulteration with low-cost glucans like sweeteners or carbohydrates that simulate their natural
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carbohydrate profile, in order to increase economical profits (Wang et al., 2010).
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At industry level, the analyses of polysaccharides for quality control are numerous, then FTIR
112
vibrational spectroscopy becomes an important analytical tool. The FTIR (Fourier Transform Infrared)
113
Spectroscopy equipment, coupled to an ATR (Attenuated Total Reflectance) device, improves the time-
114
consuming procedure for preparing samples, employing small quantity of solid, liquid or concentrated
115
analyte solutions without the necessity of additional reagents or preparative processes. This technique is
116
rapid, non-destructive and suitable to estimate the constituents, composition or pureness of samples. The
117
region located from 4000 cm-1 to 700 cm-1 shows vibrations of molecular structure through the band
118
displacement corresponding to different types of functional groups, and helps to identify quality
119
attributions of food samples with different compositions (Anjos, Campos, Ruiz, & Antunes, 2015;
120
Espinosa-Velázquez, Ramos-de-la-peña, Montanez, & Contreras-Esquivel, 2018). As a result, FTIR-
121
ATR is an important tool to analyze potential adulterated samples of food products and it may contribute
122
to detect fraudulent acts (Bureau et al., 2009; Miaw et al., 2018).
123
The aim of this paper is to employ FTIR-ATR spectroscopy to examine in depth vibrational patterns of
124
several carbohydrates frequently used as ingredients in the food industry. This report makes an approach
125
to describe the absorption bands that define the agavin polymeric structure, in order to identify changes
126
of vibrational patterns when different ingredients are added. For this purpose, artificial solid dilutions of
127
agavins with cellulose and cocoa powder, as well as three commercial samples of agavins, were
128
analyzed to determine components based on vibrational spectra of characterized standards, as a food
129
industry application case of adulterant component analysis.
130 131
2. Material and Methods
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The inulin and cellulose standards were procured by MP Biomedicals (Santa Ana, California, USA), and
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starch by Realbiotech Co. (Yeongi-Gun, Chungnam, South Korea). Roasted and powdered cocoa
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(Theobroma cacao) was acquired from Organicos Monterrey (Monterrey, Nuevo Leon, Mexico). Agave
135
fructan (agavin) sources were acquired according to the supplier listed in the Table 1.
136 137
Table 1. Types of agavin and supplemented commercial agavin suppliers.
138 139
An FTIR experimental model to develop a method to identify the presence and intensity of specific
140
bands associated with population of certain functional groups, has been reported previously (Clarck,
141
2016). The augmentation and diminution of vibrational bands may be detected through the formulation
142
of known composition powder mixtures (Lira-Ortiz et al., 2014). This methodology has been adopted in
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the report herein, to determine polysaccharide components of solid mixtures. The visualization of
144
spectra that shows an evolutive change of specific-band absorption intensities is a useful manner to
145
analyze and identify differences in the composition of a sample (Bureau, Cozzolino, & Clark, 2019;
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Espinosa-Velázquez et al., 2018; Lira-Ortiz et al., 2014). Considering that agavins may be altered
147
through its carbohydrate profile for adulteration purposes, two series of solid mixtures, agavin-cellulose
148
and agavin-cocoa powder with different composition were vibrationally analyzed. The Table 2 lists the
149
codes for the solid mixtures and their composition.
150 151
Table 2. Polysaccharide composition of powder mixtures
152 153
Standards and mixtures were analyzed by Fourier transform infrared attenuated total reflectance (FTIR-
154
ATR) spectroscopy by Perkin Elmer Spectrum GX FTIR spectrometer equipment (Waltham, MA, USA)
155
operating at 4 cm-1 resolution with 16 scans per test. The mirror velocity was 0.08 cm-1 and 35
156
interferograms were co-added before Fourier transformation. Spectra were collected from 4000 to 700
157
cm-1 in the absorbance mode, the baseline was corrected and normalized that the stronger absorption
158
band at ca. 1015 cm-1 was equaled to 1. Normalization did not alter the proportion of signals of the
159
origin spectra.
160 161
3. Results and Discussion
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3.1 FTIR Polysaccharide analysis
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The standard carbohydrates analyzed by FTIR spectroscopy are described through their basic structure
165
in solid state, to identify band patterns to discern between samples. Despite the products are defined as
166
polymers and their saccharide units are structurally similar (isomers constituted basically by pyranosides
167
and furanosides), the pattern of spectral vibrations is particular for every polysaccharide due to the
168
macromolecular arrangement (Bureau et al., 2019, 2009; Espinosa-Velázquez et al., 2018). Literature is
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frequently ambiguous about band assignments in carbohydrates, nonetheless, correct assignments of
170
bands may be done more certainly when precise wavenumbers are well localized, specifically when the
171
sample set presents a known composition about a particular functional-group characteristic band
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(Bureau et al., 2019).
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Figure 1. Infrared spectra of inulin, agavin, starch and cellulose. Functional group frequency region
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(1800 – 1500 cm-1) and fingerprint region (1200 – 900 cm-1) appear squared with dotted lines. Agavin is
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listed in Table 3 as Agavin B.
177 178
The spectral region to analyze standard carbohydrates, in this report, was from 1800 to 700 cm-1, due to
179
functional groups that mainly describe the molecular nature of biopolymers are present at this zone.
180
Absorption bands in the 1800 to 1500 cm-1 region are usually assigned to stretching vibrations of double
181
bonding atoms, commonly called functional group frequency region (Dufour, 2009). Neutral
182
polysaccharides, as standards reported herein, do not present any absorption band at these frequencies,
183
except for cases when products are not in a purified form due to heterogeneity of components or
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humidity content. The region from 1500 to 1200 cm-1 displays absorption bands belonging to single
185
bond atoms, the biopolymeric structure is displayed with medium to low intensity vibrational peaks
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(Bureau et al., 2019). The spectral area from 1200 to 900 cm-1 is the most informative and frequently
187
used in FTIR analysis of carbohydrates. It is characterized by strong overlapping bands and is generally
188
recognized as the fingerprint region (Bureau et al., 2019; Cerna et al., 2003; Pretsch, Buhlmann, &
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Badertscher, 2009; Tipson, 1968), and depicts an important difference in the structural framework for
190
products whose macroscopic characteristics are similar (Bureau et al., 2019; Cui, 2005; Stephen,
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Phillips, & Williams, 2006). Figure 1 shows a comparative view (an overlapped fashion) of the spectra
192
of the polysaccharide inulin, starch, cellulose and agavin, and a pair of squared groups of two different
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spectral signals, group frequency and fingerprint regions. Since the scheme of spectra presents high
194
overlapping, the assignment of the vibrational peaks corresponding to the FTIR analyzed
195
polysaccharides are listed in Table 3. Band were identified by comparative revision with literature
196
(Dufour, 2009; Larkin, 2011; Pretsch et al., 2009). This scheme represents an easy method to detect, not
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only the structural and qualitative difference of pure and adulterated samples, but also the composition
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of a characteristic functional group, since wavenumbers are associated with functional group and band
199
intensities with proportion in the sample (Bureau et al., 2019).
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Table 3. Assignment of vibrational bands corresponding to the FTIR analyzed carbohydrate samples
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depicted in Figures 1, 2 and 3.
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3.2 Spectral comparison of agavins
206 207
For comparative analysis purposes, the spectra of different agavin samples are depicted in Figure 2. The
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overlapped mode of displayed spectra shows the resemblance of agavin samples (Agavin A, B and C).
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As shown, the vibrational patterns exhibited analogous wavenumbers for the three samples; main
210
differences can be seen in the intensity bands belonging to Agavin A spectrum; however, taking into
211
account higher resemblance between agavins B and C, for further comparative goals of this report, the
212
agavin B will be considered as agavin standard. Assignment of their vibrational bands are listed in Table
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3.
214 215 216
Figure 2. Infrared spectra of commercial agavin products.
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3.3 Solid mixtures of agavins
219 220
3.3.1 Agavin – cellulose comparative analysis
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The spectra of agavin-cellulose mixtures with different % compositions are shown in Figure 3. Cellulose
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standard was utilized to formulate mixture samples, taking into account its low cost as dietary fiber
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source for human nutrition with bulky properties as ingredient (Robin, Schuchmann, & Palzer, 2012).
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The functional group frequency region does not present differences in band wavenumbers, matching
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bands at around 1640 cm -1. The vibrational bands in the fingerprint region present a change of peak
227
intensity with respect to the composition of ingredients, which may be associated with a band group
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“chemically sensible” to model an approach to detect ingredient composition (Bureau et al., 2019). The
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band group 1 (BG 1) at 1160 cm-1 shows that band intensity of AgvCls 100 increases when the % of
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agavin decreases to AgvCls 0. The same behavior is observed at BG 2 around 1105 cm-1, where the
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band for AgvCls 100 got decreased to medium intensity and displaced to lower wavenumber (1103 cm-
232
1
233
for AgvCls 100 when % agavin decreases to the level of AgvCls 0, as well as the stronger band in 1015
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cm-1 for AgvCls 100 resulted displaced to higher wavenumber (1028 cm-1) for AgvCls 0. The bands
235
displayed at around 993 cm-1 does not present either increasing or decreasing tendency of band
236
intensities when the agavin composition diminished. This behavior may be possibly associated with an
237
spectral composite, where different absorbances overlap, enhance or subsume one another, making
238
difficult to assign peaks to specific vibration and then, identifying a tendency (Bureau et al., 2019). In
239
addition, an important change is detected in the BG 4; the band at 926 cm-1 displayed by AgvCls 100
240
decreased to disappearance with the reduction of % agavin in the solid mixture, which results in the
241
appearance of bands at 897 cm-1 by both AgvCls 10 and AgvCls 0, the corresponding-to-cellulose band
) as shown by AgvCls 0 (see Table 3). The BG 3 illustrates also the increasing of the band at 1053 cm-1
242
spectrum. The displacements of wavenumber showed by BG2 and BG4 possibly describes the change
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from pentoses to hexoses in the composition of the polymeric framework of the mixture components.
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The displayed spectra (Figure 3) illustrate, not only a comparative overlapped view of the spectra, which
245
allows to identify increasing, decreasing and displacements of absorption bands, but also the main
246
absorption peaks of agavins, which are squared and selected as functional group signals for further
247
analysis of commercial agavin samples.
248 249 250
Figure 3. Comparative visualization of spectra for agavin mixed with cellulose with different
251
composition. Band Group (BG) indicates evolution in specific wavenumbers and absorption intensity of
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specific vibration bands.
253 254
3.3.2 Agavin – cocoa comparative analysis
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A series of agavin-cocoa solid mixtures were analyzed to detect the change of band intensities and
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displacements when composition of agavin decreases; the spectra are displayed in the Figure 4. The
258
assignment of the vibrational peaks corresponding to the FTIR analyzed samples are listed in Table A.1
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(Supplementary information). The composition of cocoa in the agavin mixtures changes from 0% to
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10% (agavin from 100% to 90%), as it can be observed by the colored lines corresponding to the
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indicated mixture in the figure. The bands localized at the functional group frequency zone for AgvCca
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90 shows a noticeable peak that merges at 1735 cm-1, as well as a band at around 1656 cm-1 got more
263
intense when the cellulose content in the mixture got increased. These bands are associated with
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esterified carbonyls from pectic material (Redgwell, Trovato, & Curti, 2003), and with humidity in both
265
cocoa powder (Chung, Iiyama, & Han, 2003; Redgwell et al., 2003; Sotelo & Alvarez, 1991; Velázquez
266
de la cruz & Martín-Polo, 2000) and agavins (Kačuráková & Wilson, 2001). The vibration band at 1267
267
cm-1, displayed by AgvCca 90 corresponds to vibrations of C-H and C-O bonds (Bureau et al., 2019;
268
Lecumberri et al., 2007; Liendo, Padilla, & Quintana, 1997; Redgwell et al., 2003; Sotelo & Alvarez,
269
1991), and the band at 1253 cm-1 to N-H of proteinic material present in cocoa powder (Larkin, 2011).
270
With respect to the vibrational pattern at fingerprint region, the evolution of the band intensities
271
resemblances to the described in Figure 3. At 1158 cm-1 and around 1120 cm-1 wavenumbers, there are
272
increments in peak intensities showed by AgvCca 90, which also showed a displacement to a lower
273
wavenumber, from 1124 cm-1 to 1115 cm-1, with respect to the rest of AgvCca composites. Finally, the
274
band at 926 cm-1 for AgvCca 90 appears with a slight decrease in the absorbance intensity compared
275
with the rest of peaks; and at 869 cm-1, the bands did not exhibit an intensity change. The overlapped
276
spectra (Figure 4) allow to detect that shown spectra are very similar when the content of cocoa powder
277
changes from 0% up to 5%; nevertheless, the solid mixture with 10% of cocoa powder displayed
278
important variations in peak intensities at functional group frequency zone, unlike fingerprint region
279
where the intensity variations were minor.
280 281 282
Figure 4. Infrared spectra of different composites of agavin mixed with cocoa powder in a range of
283
100% to 90%.
284 285
A complementary analysis of the solid mixtures with higher differences in % composition of agavin-
286
cocoa was carried out with the purpose of describing the vibrational profile of composites. The spectra
287
are displayed in the Figure 5 and are respectively illustrated by different color lines. This schematization
288
exhibits an evolutive change of absorbance intensities and shifts of vibrational bands when the cocoa
289
component gets increased in the composite, in a higher degree than the showed in Figure 4, and even it
290
may be used eventually as calibration curve for analogous systems when a specific functional group is
291
selected, as reported previously (Espinosa-Velázquez et al., 2018).
292 293
The comparison among depicted samples in Figure 4 and 5 allows to identify that absorption signals
294
mainly undergo an augmentation in absorbance, as well as broad bands got split when the agavin
295
composition diminished in the different samples from 1800 cm-1 to 1015 cm-1; bands at lower
296
wavenumbers behaved in a decreasing manner. It is detectable the augmentation of the band at around
297
1740 cm-1 for AgvCca 80, from very weak to medium intensity, which even got split to the bands at
298
1743 cm-1, 1735 cm-1 and 1729 cm-1 for AgvCca 0. These bands are associated with esterified carbonyl
299
C=O group of fatty acids (Lecumberri et al., 2007; Liendo et al., 1997), acetylated carbonyls of pectic
300
material and ketones of antioxidant polyphenols present in the cocoa powder (Batista, de Andrade,
301
Ramos, Dias, & Schwan, 2016; Carrillo, Londoño-Londoño, & Gil, 2014; Lecumberri et al., 2007). The
302
broad and very weak band at 1643 cm-1 displayed for AgvCca 100 got increased and split in two bands
303
at 1653 cm-1 and 1623 cm-1 with medium intensity. These absorption peaks correspond to the stretching
304
of a C=O bond from an amide type I, N-H bending and C-C stretching of phenyl groups from
305
polyphenols present in cocoa powder (Batista et al., 2016; Carrillo et al., 2014; Larkin, 2011; Pretsch et
306
al., 2009). The bands at 1549 cm-1 and 1523 cm-1 for AgvCca 0, appeared and got increased from a very
307
broad and almost non-existent band at 1525 cm-1 for AgvCca 80 spectra, which is associated with the
308
symmetrical stretching of the atomic bonding system N-C=O that belong to amide type II and also the
309
N-H bending from protein content of the cocoa (Larkin, 2011; Redgwell et al., 2003; Sotelo & Alvarez,
310
1991). Absorption bands from lower wavenumbers than 1500 cm-1 down to 1280 cm-1 are mainly caused
311
by the presence of C-H bond from a variety of aliphatic and phenyl groups and by different vibration
312
types (see Table A.3 Supplementary material). The depicted bands at 1270 cm-1 and 1219 cm-1 by
313
AgvCca 100 evolved to a set of several absorption peaks showed by the AgvCca 0 sample. Vibrational
314
band group between 1280 – 1200 cm-1 region may be assigned to C-O stretching, O-H in-plane-bending
315
carbohydrates and C-H in-plane-bending for phenyls present in antioxidant and aliphatic hydrocarbon
316
compounds present in fatty acids of cocoa. A medium intensity absorption peak at 1248 cm-1 may be
317
associated with C-O-C and N-H stretching and belongs to acetylated carbonyls and amino acid groups
318
from pectic material, proteins, fatty acids and flavonoid ketones present in cocoa (Batista et al., 2016;
319
Carrillo et al., 2014; Lecumberri et al., 2007). The weak shoulder type peak at 1163 cm-1 for AgvCca
320
100 became split with the increment of cocoa content of the sample AgvCca 0, which are displayed as
321
medium size bands at 1176 cm-1 and 1150 cm-1. The band at 1123 cm-1 for AgvCca 100 was also split to
322
strong absorption peaks and shifted to 1105 cm-1, 1090 cm-1 and 1074 cm-1 for AgvCca 0. These split
323
bands correspond to C-O-C bonds of carbohydrate heterocyclic rings and glycosidic links associated
324
with insoluble fiber, which are also overlapped with some possible absorption peaks of the C-O-C bond
325
that belongs to the ester group of fatty acids present in the triacylglycerols of cocoa component
326
(Lecumberri et al., 2007). All spectra coincide with the stronger band at 1016 cm-1 that is assigned to C-
327
O-C bonds of intra and inter monosaccharide rings. The band at 930 cm-1 for AgvCca 100 diminished
328
almost to disappearance in AgvCca 0, with a reduction of agavin content. These bands at 1016 cm-1 and
329
932 cm-1 are associated with the spectral anomeric frequency region, which is defined by the symmetric
330
stretching vibrations of C-O-C glycosidic bonds of the polysaccharide framework (Cerna et al., 2003;
331
Chung et al., 2003; Nikonenko, Buslov, Sushko, & Zhbankov, 2005; Pretsch et al., 2009; Sekkal, Dincq,
332
Legrand, & Huvenne, 1995; Tipson, 1968). The medium size band at 930 cm-1 showed by AgvCca 100
333
decreased to a very weak shoulder type band at 922 cm-1 and got displaced to a lower wavenumber peak
334
displayed at 893 cm-1 by AgvCca 0, a similar band showed by cellulose in Figure 1 and Figure 3. This
335
evolutive band displacement from 930 cm-1 to 893 cm-1 wavenumbers coincides with the increasing of
336
insoluble dietary fiber associated with cellulose present in cocoa (Lecumberri et al., 2007).
337 338 339
Figure 5. Vibrational spectra of different composition of agavin mixed with cocoa powder in a range of
340
100% to 0%.
341 342
3.4 Vibrational analysis of commercial supplemented agavins
343 344
In order to analyze commercial supplemented agavin products, three agavins added with nutritive-value
345
ingredients were analyzed to identify their vibrational pattern, to compare them with composites
346
previously described herein and estimate composition. The commercial agavins are added with Aloe
347
vera, antioxidants (labeled as extract of green tea, cranberry, chamomile and vitamin D) and cocoa
348
(Thereobroma cocoa). The spectra of commercial products and agavin are depicted in Figure 6; agavin
349
standard is shown in the figure just for comparative goals. The assignment of the vibrational peaks
350
corresponding to the FTIR-ATR analyzed samples are listed in Table A.3 (supplementary material).
351
Bands around functional group frequency and fingerprint regions show absorption peaks with a high
352
similarity to the agavins´ (Figure 2). Nevertheless, particularities in specific bands are associated with
353
the nature of the supplemented ingredient. Regarding the functional group frequency zone, Metlin® Aloe
354
exhibited a very weak and broad pair of absorptions at 1640 cm-1 and 1570 cm-1, corresponding to
355
vibrations that belong to moisture, C=O stretching from uronic sugars and polyphenols; as well as the
356
band at 1570 cm-1 is associated with the carboxylate moiety (COO-) stretching (Chang, Chen, & Feng,
357
2011; Kiran & Rao, 2014; Okamura, Asai, Hine, & Yagi, 1996). Metlin® Antiox displayed also weak
358
and broad absorption peaks at 1682 cm-1, 1629 cm-1 and 1608 cm-1, which correspond to stretching of
359
C=O carbonyl from amides type I and N-H bending vibrations that belong to polyphenols supplied by
360
antioxidant supplement (Santos-Sánchez, Salas-Coronado, Villanueva-Cañongo, & Hernández-Carlos,
361
2019). Viv Agave® cocoa presents a similar spectrum displayed by the composite AgvCca 80 (Figure
362
5), whichalso displayed vibrational bands at 1737 cm-1 and 1651 cm-1. With respect to 1500 – 1200 cm-1
363
spectral zone, differences are basically described by the absorption intensity of peaks assigned to
364
aliphatic and aromatic C-H stretchings from carbohydrates of Aloe vera, pectic material from cocoa,
365
and also from polyphenols that are present in antioxidants(band assignation are shown in Table A.3 of
366
the supplementary material). The fingerprint zone of the samples displayed a low-size shoulder at 1157
367
cm-1 for Viv Agave® cocoa, which in common with the peak at 1107 cm-1 exhibit high resemblance to
368
the composite AgvCca60 (Figure 5); the intensity of these two absorption bands (around 0.3 Uabs for
369
band at 1157 cm-1 and 0.4 Uabs for band at 1107 cm-1) indicate that the proportion of cocoa powder in
370
Viv Agave® cocoa is in between AgvCca 80 and AgvCca 60 (20 and 40% of cocoa powder
371
composition). Absorption bands for Metlin® Aloe and Metlin® Antiox displayed high correlation, even
372
with agavin spectra when observing vibrational patterns in lower-wavenumber spectral zone.
373 374 375
Figure 6. Comparative scheme of spectra belonging to supplemented agavins Metlin® Aloe, Metline®
376
Antiox, Viv Agave® cocoa and Agavin.
377 378 379
4. Conclusions
380
The FTIR-ATR spectroscopy was used to analyze the spectra of standard carbohydrates and commercial
381
samples to identify characteristic peaks to explain their structural composition. A comparative analysis
382
of starch, inulin and cellulose with agave fructan (agavin) displayed particularities punctually described
383
for identification purposes at specific regions of the FTIR spectral window. The compilation of spectra
384
from different samples resulted an adequate method to identify changes in polysaccharide composition,
385
with individual spectra as well as with solid mixtures of standards. This schematization provides a
386
suitable manner to observe an evolutive behavior of the band intensities in accordance with the
387
concentration of the component, displaying the presence, absence, lengthening or weakening of specific
388
vibrational bands, as well as displacement of specific wavenumbers.
389
In this sense, the evaluation of the spectral fingerprint region allowed to describe absorption bands
390
susceptible to analyze the composition of artificial solid mixtures. The examination of agavin- cellulose
391
and agavin-cocoa systems resulted informative to observe change in band intensities and shifts, which
392
led to group peaks that may be even used for quantitative composition. Agavin-cellulose serial dilution
393
spectra showed stronger intensity peaks at around 1160 - 1105 cm-1 when the composition of agavin
394
decreased, and an opposite comportment with the absorption peak at 926 cm-1, where the band got
395
diminished with the reduction of agavin composition in the mixture. The system composed by agavin-
396
cocoa also showed similar behavior, with additional characteristic absorption bands that belongs to the
397
cocoa components, which helps to identify alterations of an agavin sample.
398
When a set of three commercial samples of supplemented agavins with Aloe vera, antioxidants and
399
cocoa powders were analyzed vibrationally, several signals were identified promptly considering
400
previous analyzed systems. Since the agavins were supplements with those mentioned specific type of
401
ingredients, based on their structure, the corresponding vibrational peak were readily identified. The
402
Aloe vera and antioxidant supplements did not alter the vibrational patter of the fingerprint region for
403
agavins, even the supplemented agavin with cocoa; just the vibration peak around 1160 cm-1 to 1107 cm-
404
1
405
spectroscopic analysis of agave solid mixtures is a valuable tool to procure information of food
406
ingredients for comparative goals with fructan-type commercial supplemented products, in order of
407
discriminate possible adulterations in related supplemented products.
zone displayed a slightly difference in the vibrational pattern for system analyzed. Finally, this
408 409 410 411
Acknowledgements
412
The first author thanks to CONACyT Mexico for the financial support of postdoctoral fellowship to the
413
first author. This report was partially financed and supported by the project SEP-PRODEP UCOL-
414
NPTC-250 (Mexico).
415 416
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Table 1. Types of agavin and supplemented commercial agavin suppliers. Entry
Commercial name
Supplier
Agavin A
Agave inulin
Ingredion. Monterrey, Nuevo Leon. Mexico.
Agavin B
Agave inulin
Vaserco Co. Zapopan, Jalisco, Mexico.
Agavin C
Agave inulin
Edulag. Villa Corona, Jalisco, Mexico.
Product A
Metlin® Aloe
BioTrendy Co. Zapopan, Jalisco. Mexico.
Product B
Metlin® Antioxidants
BioTrendy Co. Zapopan, Jalisco. Mexico.
Product C
Viv Agave® Cocoa
Vivagave Foods LLC. Mountlake Terrace, Washington, USA.
578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601
Table 2. Polysaccharide composition of powder mixtures Sample code
Agavin A
Cellulose
g
%
g
%
AgvCls 100
1.000
100
0.000
0
AgvCls 30
0.300
30
0.700
70
AgvCls 10
0.100
10
0.900
90
AgvCls 0
0.000
0
1.000
100
Agavin A
602 603 604 605 606 607 608 609 610 611 612 613 614 615 616
Cocoa powder
AgvCca 100
1.000
100.0
0.000
0.00
AgvCca 99.5
0.995
99.5
0.005
0.05
AgvCca 99
0.990
99.0
0.010
1.00
AgvCca 95
0.950
95.0
0.050
5.00
AgvCca 90
0.900
90.0
0.100
10.0
AgvCca 80
0.800
80.0
0.200
20.0
AgvCca 60
0.600
60.0
0.400
40.0
AgvCca 40
0.400
40.0
0.600
60.0
AgvCca 20
0.200
20.0
0.800
80.0
AgvCca 0
0.000
0.00
1.000
100.0
Table 3. Assignment of vibrational bands corresponding to the FTIR analyzed carbohydrate samples depicted in Figures 1, 2 and 3. Inulin
Starch
Cellulose
Agavin A
Agavin B
Agavin C
AgvCls100
AgvCls30
AgvCls10
AgvCls0
Bond Vibration
1640, vw
1643, vw
1643, vw
1643, vw
1642, vw
1643, vw
1643, vw
1639, vw
1637, vw
1640, vw
H-O-H st
1452, vw
1451, vw
1452, vw
1452, vw
1452
1452
1427, vw
1428, vw
1455, vw
1458, vw
C-H methyl oop bd; methylene, bd
1455, vw
C-H methyl oop bd; methylene, bd 1441, vw
1427, vw
1429, vw 1416, vw
1370, vw
1369, vw
1418, w
1420, w
1420, w
1420, w
1368, vw
1371, vw
1366, vw
1368, vw
1430, vw
1335, vw
1367, vw
1369, vw
1370, vw
1334, vw 1314, vw
1278, vw
1279, vw
1335, vw
1266, vw
1330, vw
1270, vw
1332, vw
1269, vw
1335, vw
1266, vw
1333, vw
1334, vw
1333, w
C-H methyl ip bd
1313, vw
1316, w
1316, w
C-H methyl ip bd
1278, vw
1280, vw
1282, vw
C-H methyl ip bd
1246, vw
C-O-H st; C-O-H ip bn
1241, vw
C-O-H st; C-O-H ip bn
1221, vw 1200, vw
1202, vw
1160, w 1144, m
1216, vw
1218, vw
1218, vw
1216, vw
1160, w sh
1157, vw sh
1158, vw sh
1160 vw sh
1122, w
1122, w
1124, w
1124, m
1203, vw 1159, w
1217, vw
C-O-H st; C-O-H ip bn
1201, vw
1201, vw
1202, vw
C-O-H st; C-O-H ip bn
1162, w
1160, w
1160, w
C-O-H, st; C-O-C st inter
1147, m
C-O-H, st; C-O-C st inter
1123, w 1104, m
1103, w
1103, m
1100, w
C-O-H, st; C-O-C st inter 1106, m
1105, m
1103, m
1051, s sh
1052, vs
1053, vs
C-O-H st; C-O-C intra oop st
1028, vs
1028, vs
1028, vs
C-O-H st; C-O-C intra oop st
997, vs sh
994, s sh
1076, m 1052, s sh
1040, s
1028, vs
1050, s sh
1050, s sh
1047, s sh
1047, s sh
1015, vs
1014, vs
1015, vs
1015, vs
986, s
990, s sh
930, w
879, vw sh
C-O-H st; C-O-C intra oop st
999, s sh 989, s sh
988, s sh
988, s sh
937, m
900, vw
926, m
927, m
926, m
987, s
C-O-C st intra, st inter C-O-C st intra, st inter C-O-C st intra, inter; C-O-H, st
926, m 897, w
871, vw
873, vw
873, vw
873, vw
C-O-C st intra, st inter
935, m
897, vw 859, vw
C-O-H, st; C-O-C st inter C-O-H st; C-O-C intra oop st
1054, s 1029, vs
995, vs
C-H methyl oop bd; methylene, bd C-H methyl oop bd; methylene, bd
1315, vw
1249, vw
C-H methyl oop bd; methylene, bd C-H methyl oop bd; methylene, bd; C-N st
1360, vw 1334, vw
C-H methyl oop bd; methylene, bd
873, vw sh
897, w
C-O-C st intra, inter; C-O-H, st C-O-C st intra, inter; C-O-H, st
Legends of bond types is as follows: st, stretching; bn, bending; ip, in-plane; oop, out-of-plane; s, symmetrical; as, asymmetrical; s, strong; vs, very strong; m, medium; w, weak; vw, very weak; sh, shoulder; blank, not observed; intra: cyclic ring; inter: exocyclic glycosidic bond. Bold letters represent atom bonding vibration.
Highlights • • • • •
FTIR-ATR spectroscopy is a rapid method to identify structure of polysaccharide samples. Vibrational spectra of ingredients may be used to identify adulterations in foods. Agavin and polysaccharides were characterized vibrationally to identify interest peaks. Absorption peaks assignments may be detected to find anomalies in solid mixtures. Commercial supplemented agavins displayed signals identified in the spectra of standards.
Conflict of interest declaration We, the authors, have no competing interests to declare.
Author Statement Oscar F. Vázquez-Vuelvas: Conceptualization, Methodology, Formal analysis, Writing – Original Draft, Writing - Review & Editing, Visualization. Félix A. Chávez-Camacho: Investigation, Data curation, Validation, Software. Jorge A. Meza-Velázquez: Resources, Formal Analysis, Writing - Review & Editing.
Emilio Mendez-Merino: Resources,
Formal Analysis, Writing - Review & Editing. Merab M. Ríos-Licea: Resources, Formal Analysis,
Writing
-
Review
&
Editing.
Juan
Carlos
Contreras-Esquivel:
Conceptualization, Methodology, Formal analysis, Resources, Writing - Review & Editing, Visualization, Project administration.
S0268-005X(18)31730-2
DOI:
https://doi.org/10.1016/j.foodhyd.2020.105642
Reference:
FOOHYD 105642
To appear in:
Food Hydrocolloids
Received Date: 3 September 2018 Revised Date:
3 January 2020
Accepted Date: 3 January 2020
Please cite this article as: Vázquez-Vuelvas, O.F., Chávez-Camacho, Fé.A., Meza-Velázquez, J.A., Mendez-Merino, E., Ríos-Licea, M.M., Contreras-Esquivel, J.C., A comparative FTIR study for supplemented agavin as functional food, Food Hydrocolloids (2020), doi: https://doi.org/10.1016/ j.foodhyd.2020.105642. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2020 Published by Elsevier Ltd.
1
A comparative FTIR study for supplemented agavin as functional food
2 3
Oscar F. Vázquez-Vuelvas,a,* Félix A. Chávez-Camacho,b Jorge A. Meza-Velázquez,c Emilio Mendez-
4
Merino,d Merab M. Ríos-Licea,d Juan Carlos Contreras-Esquivel.b, e, *
5 6
a
7
de Colima, Km 9 Carr. Colima-Coquimatlan s/n. Coquimatlan, Colima. C. P. 28400, Mexico.
8
b
9
Universidad Autónoma de Coahuila. Saltillo, Coahuila. 25280. México.
Laboratory of Biochemical Engineering and Bioprocesses, Faculty of Chemical Sciencies, Universidad
Laboratory of Applied Glycobiotechnology, Food Research Department, School of Chemistry,
10
c
11
Palacio, Durango. C. P. 35010, Mexico.
12
d
Sigma Alimentos Co., Torre Sigma, San Pedro Garza Garcia, Nuevo Leon. C. P. 66260, Mexico.
13
e
Research and Development Center, Coyotefoods Biopolymer and Biotechnology Co., Simon Bolivar
14
851-A, Saltillo, Coahuila. C. P. 25000. Mexico.
Food Science Laboratory, School of Chemistry, Universidad Juarez del Estado de Durango, Gomez
15 16 17 18 19 20 21 22 23
Corresponding authors:
24 25
[email protected]
26
[email protected]
27 28 29 30 31
* These authors contributed equally to this work.
32 33
Abstract
34 35
Functional foods are products focused to human consumption with benefits to different physiologic
36
aspects in order to prevent diverse metabolic problems in the body. Prebiotics recently have been started
37
to be employed as functional foods, and fructans as inulin or agave inulin, known as agavin, represent a
38
valuable source of them. Standard polysaccharides as starch, inulin, cellulose and agavin were
39
vibrationally analyzed by FTIR spectroscopy, as well as solid mixtures with different agavin-cellulose
40
and agavin-cocoa ratios, to identify important absorption peaks to detect evolutive changes of bands in
41
absorbance intensities and wavenumbers displacements, in order to employ this information for possible
42
adulteration in this prebiotic functional foods. Three commercial products identified as supplemented
43
agavins with Aloe vera, antioxidants and cocoa were vibrationally analyzed and described by
44
comparative visualization with standard solid mixtures for detecting discrepancies with ingredient
45
compositions. The vibrational patterns displayed by standard polysaccharides allowed to identify
46
frequency zones for making an approach to elucidate standards; furthermore, solid mixtures of standards
47
described the evolution of absorption peaks proportionally to the ratio of the samples. Spectra of agavin-
48
cellulose and agavin-cocoa solid mixtures exhibited an increment in bands associated with C-O and C-
49
O-C between 1176 cm-1 and 1074 cm-1 when the agavin content diminished in the mixture; an opposite
50
behavior was depicted at 926 cm-1 absorption band, intensity
51
decreased. The spectra of commercial agavins provided the information to identify structural similarities
52
with the absorption bands shown by polysaccharide standards, which made it possible to identify the
53
presence of the components of interest.
54 55 56 57 58 59 60 61 62
Keywords: FTIR, fructan, agavin, polysaccharide, functional food
decreased when the agavin ratio
63 64
1. Introduction
65
Functional foods represent a series of food products with benefits to diverse physiological aspects for
66
humans (Konar et al., 2018). Functional foods may be described as nutriments that affect positively to
67
different targets in the body to promote health (Donato-Capel et al., 2014), by cure and/or prevention of
68
diverse
69
functional food characteristics associate with a recent definition of prebiotic concept, since they are
70
substrates that are selectively utilized by gastrointestinal microorganisms to confer health benefit to the
71
host (Konar et al., 2018).
72
The elaboration of functional foods requires supplements with a high nutritional value, since they have
73
been gaining interest, an increment in their value has occurred; as a consequence, functional foods have
74
become economically valuable (Oreopoulou & Tzia, 2007). In this sense, hydrocolloids are widely used
75
to produce functional foods and are catalogued as fibre-rich foods or dietary fiber; they are defined as
76
any carbohydrate that does not hydrolyze in the gastrointestinal tract. Nevertheless, a more complete
77
definition is about those carbohydrate polymers with ten or more monomeric units, which are not
78
hydrolyzed by endogenous enzymes in the small intestine of humans (Perry & Ying, 2016).
79
Fructans are a group of soluble polymeric carbohydrates considered as dietary fiber according to
80
structural, analytical and physiological concepts (Handa, Goomer, & Siddhu, 2012). They are
81
constituted basically by fructose units; and after starch, fructans are the most abundant non-structural
82
polysaccharides (Mancilla-Margalli, López, & López, 2006; Muñoz-Gutiérrez, Rodríguez-Alegría, &
83
López Munguía, 2009; Velázquez-Martínez et al., 2014). From the structural point of view, fructans are
84
macromolecules naturally synthetized from sucrose and named considering the linkage type present in
85
the carbohydrate chain. Inulins are fructans with the predominant β(2-1) fructosydic bond, and levans
86
when the main fructosydic linkage is β(2-6), both linked to the fructosyl unit of saccharose (Muñoz-
87
Gutiérrez et al., 2009). In addition, fructans obtained from Agave tequilana plants are known as agavins
88
and are considered a series with a highly branched chains defined by linked fructosyl units with a
89
combination of β(2-1) and β(2-6) fructosydic bonds (Mancilla-Margalli et al., 2006; Muñoz-Gutiérrez et
90
al., 2009; Waleckx, Gschaedler, Colonna-Ceccaldi, & Monsan, 2008). The fructan biopolymer presents
91
different degree of polymerization; the number of linked fructosyl residues may vary from 2 to 60
metabolic disorders or illnesses (Dubey, Toh, & Yeh, 2018; Konar et al., 2018). These
92
residual units, and comparatively to sucrose, they are 10% as sweet as sucrose, an attractive organoleptic
93
property that enhances palatability of fructans as a functional food ingredient. Oligomer molecules are
94
constituted by no more than ten fructofuranosyl units, and are better known as fructooligosaccharides
95
(FOS) or oligofructose (Apolinário et al., 2014; Brownlee, 2011; Franck, 2006; Mensink, Frijlink, Van
96
Der Voort Maarschalk, & Hinrichs, 2015).
97
In Mexico, the agave species represent an appreciated bioresource due to several of them are
98
economically important for producing a wide variety of distilled and fermented beverages (Ávila-
99
Fernández, Galicia-Lagunas, Rodríguez-Alegría, Olvera, & López-Munguía, 2011). Agave tequilana,
100
raw material to produce Tequila, is mainly harvested to this purpose (Montañez-Soto, Venegas-
101
gonzález, Vivar-Vera, & Ramos-Ramirez, 2011); however, agave fructans have recently become
102
attractive ingredients because of its characteristic as dietary fiber and prebiotic activity. Numerous
103
reports indicate that consumption of specific hydrocolloids as fructans may regulate the composition of
104
the intestinal flora, to promote the production of biologically short chain fatty acids in the human large
105
bowel, especially the butyric acid, which has important anticarcinogenic effects (Li & Nie, 2016).
106
The agave inulin (agavin) recently started to be commercially available in Mexico as a supplement; this
107
makes agavin powder become valuable as a food supplement from the economical point of view, due to
108
the value as a dietary fiber source and sweetener. Consequently, agavin powder may be a target of
109
adulteration with low-cost glucans like sweeteners or carbohydrates that simulate their natural
110
carbohydrate profile, in order to increase economical profits (Wang et al., 2010).
111
At industry level, the analyses of polysaccharides for quality control are numerous, then FTIR
112
vibrational spectroscopy becomes an important analytical tool. The FTIR (Fourier Transform Infrared)
113
Spectroscopy equipment, coupled to an ATR (Attenuated Total Reflectance) device, improves the time-
114
consuming procedure for preparing samples, employing small quantity of solid, liquid or concentrated
115
analyte solutions without the necessity of additional reagents or preparative processes. This technique is
116
rapid, non-destructive and suitable to estimate the constituents, composition or pureness of samples. The
117
region located from 4000 cm-1 to 700 cm-1 shows vibrations of molecular structure through the band
118
displacement corresponding to different types of functional groups, and helps to identify quality
119
attributions of food samples with different compositions (Anjos, Campos, Ruiz, & Antunes, 2015;
120
Espinosa-Velázquez, Ramos-de-la-peña, Montanez, & Contreras-Esquivel, 2018). As a result, FTIR-
121
ATR is an important tool to analyze potential adulterated samples of food products and it may contribute
122
to detect fraudulent acts (Bureau et al., 2009; Miaw et al., 2018).
123
The aim of this paper is to employ FTIR-ATR spectroscopy to examine in depth vibrational patterns of
124
several carbohydrates frequently used as ingredients in the food industry. This report makes an approach
125
to describe the absorption bands that define the agavin polymeric structure, in order to identify changes
126
of vibrational patterns when different ingredients are added. For this purpose, artificial solid dilutions of
127
agavins with cellulose and cocoa powder, as well as three commercial samples of agavins, were
128
analyzed to determine components based on vibrational spectra of characterized standards, as a food
129
industry application case of adulterant component analysis.
130 131
2. Material and Methods
132
The inulin and cellulose standards were procured by MP Biomedicals (Santa Ana, California, USA), and
133
starch by Realbiotech Co. (Yeongi-Gun, Chungnam, South Korea). Roasted and powdered cocoa
134
(Theobroma cacao) was acquired from Organicos Monterrey (Monterrey, Nuevo Leon, Mexico). Agave
135
fructan (agavin) sources were acquired according to the supplier listed in the Table 1.
136 137
Table 1. Types of agavin and supplemented commercial agavin suppliers.
138 139
An FTIR experimental model to develop a method to identify the presence and intensity of specific
140
bands associated with population of certain functional groups, has been reported previously (Clarck,
141
2016). The augmentation and diminution of vibrational bands may be detected through the formulation
142
of known composition powder mixtures (Lira-Ortiz et al., 2014). This methodology has been adopted in
143
the report herein, to determine polysaccharide components of solid mixtures. The visualization of
144
spectra that shows an evolutive change of specific-band absorption intensities is a useful manner to
145
analyze and identify differences in the composition of a sample (Bureau, Cozzolino, & Clark, 2019;
146
Espinosa-Velázquez et al., 2018; Lira-Ortiz et al., 2014). Considering that agavins may be altered
147
through its carbohydrate profile for adulteration purposes, two series of solid mixtures, agavin-cellulose
148
and agavin-cocoa powder with different composition were vibrationally analyzed. The Table 2 lists the
149
codes for the solid mixtures and their composition.
150 151
Table 2. Polysaccharide composition of powder mixtures
152 153
Standards and mixtures were analyzed by Fourier transform infrared attenuated total reflectance (FTIR-
154
ATR) spectroscopy by Perkin Elmer Spectrum GX FTIR spectrometer equipment (Waltham, MA, USA)
155
operating at 4 cm-1 resolution with 16 scans per test. The mirror velocity was 0.08 cm-1 and 35
156
interferograms were co-added before Fourier transformation. Spectra were collected from 4000 to 700
157
cm-1 in the absorbance mode, the baseline was corrected and normalized that the stronger absorption
158
band at ca. 1015 cm-1 was equaled to 1. Normalization did not alter the proportion of signals of the
159
origin spectra.
160 161
3. Results and Discussion
162 163
3.1 FTIR Polysaccharide analysis
164
The standard carbohydrates analyzed by FTIR spectroscopy are described through their basic structure
165
in solid state, to identify band patterns to discern between samples. Despite the products are defined as
166
polymers and their saccharide units are structurally similar (isomers constituted basically by pyranosides
167
and furanosides), the pattern of spectral vibrations is particular for every polysaccharide due to the
168
macromolecular arrangement (Bureau et al., 2019, 2009; Espinosa-Velázquez et al., 2018). Literature is
169
frequently ambiguous about band assignments in carbohydrates, nonetheless, correct assignments of
170
bands may be done more certainly when precise wavenumbers are well localized, specifically when the
171
sample set presents a known composition about a particular functional-group characteristic band
172
(Bureau et al., 2019).
173 174
Figure 1. Infrared spectra of inulin, agavin, starch and cellulose. Functional group frequency region
175
(1800 – 1500 cm-1) and fingerprint region (1200 – 900 cm-1) appear squared with dotted lines. Agavin is
176
listed in Table 3 as Agavin B.
177 178
The spectral region to analyze standard carbohydrates, in this report, was from 1800 to 700 cm-1, due to
179
functional groups that mainly describe the molecular nature of biopolymers are present at this zone.
180
Absorption bands in the 1800 to 1500 cm-1 region are usually assigned to stretching vibrations of double
181
bonding atoms, commonly called functional group frequency region (Dufour, 2009). Neutral
182
polysaccharides, as standards reported herein, do not present any absorption band at these frequencies,
183
except for cases when products are not in a purified form due to heterogeneity of components or
184
humidity content. The region from 1500 to 1200 cm-1 displays absorption bands belonging to single
185
bond atoms, the biopolymeric structure is displayed with medium to low intensity vibrational peaks
186
(Bureau et al., 2019). The spectral area from 1200 to 900 cm-1 is the most informative and frequently
187
used in FTIR analysis of carbohydrates. It is characterized by strong overlapping bands and is generally
188
recognized as the fingerprint region (Bureau et al., 2019; Cerna et al., 2003; Pretsch, Buhlmann, &
189
Badertscher, 2009; Tipson, 1968), and depicts an important difference in the structural framework for
190
products whose macroscopic characteristics are similar (Bureau et al., 2019; Cui, 2005; Stephen,
191
Phillips, & Williams, 2006). Figure 1 shows a comparative view (an overlapped fashion) of the spectra
192
of the polysaccharide inulin, starch, cellulose and agavin, and a pair of squared groups of two different
193
spectral signals, group frequency and fingerprint regions. Since the scheme of spectra presents high
194
overlapping, the assignment of the vibrational peaks corresponding to the FTIR analyzed
195
polysaccharides are listed in Table 3. Band were identified by comparative revision with literature
196
(Dufour, 2009; Larkin, 2011; Pretsch et al., 2009). This scheme represents an easy method to detect, not
197
only the structural and qualitative difference of pure and adulterated samples, but also the composition
198
of a characteristic functional group, since wavenumbers are associated with functional group and band
199
intensities with proportion in the sample (Bureau et al., 2019).
200 201
Table 3. Assignment of vibrational bands corresponding to the FTIR analyzed carbohydrate samples
202
depicted in Figures 1, 2 and 3.
203 204 205
3.2 Spectral comparison of agavins
206 207
For comparative analysis purposes, the spectra of different agavin samples are depicted in Figure 2. The
208
overlapped mode of displayed spectra shows the resemblance of agavin samples (Agavin A, B and C).
209
As shown, the vibrational patterns exhibited analogous wavenumbers for the three samples; main
210
differences can be seen in the intensity bands belonging to Agavin A spectrum; however, taking into
211
account higher resemblance between agavins B and C, for further comparative goals of this report, the
212
agavin B will be considered as agavin standard. Assignment of their vibrational bands are listed in Table
213
3.
214 215 216
Figure 2. Infrared spectra of commercial agavin products.
217 218
3.3 Solid mixtures of agavins
219 220
3.3.1 Agavin – cellulose comparative analysis
221 222
The spectra of agavin-cellulose mixtures with different % compositions are shown in Figure 3. Cellulose
223
standard was utilized to formulate mixture samples, taking into account its low cost as dietary fiber
224
source for human nutrition with bulky properties as ingredient (Robin, Schuchmann, & Palzer, 2012).
225
The functional group frequency region does not present differences in band wavenumbers, matching
226
bands at around 1640 cm -1. The vibrational bands in the fingerprint region present a change of peak
227
intensity with respect to the composition of ingredients, which may be associated with a band group
228
“chemically sensible” to model an approach to detect ingredient composition (Bureau et al., 2019). The
229
band group 1 (BG 1) at 1160 cm-1 shows that band intensity of AgvCls 100 increases when the % of
230
agavin decreases to AgvCls 0. The same behavior is observed at BG 2 around 1105 cm-1, where the
231
band for AgvCls 100 got decreased to medium intensity and displaced to lower wavenumber (1103 cm-
232
1
233
for AgvCls 100 when % agavin decreases to the level of AgvCls 0, as well as the stronger band in 1015
234
cm-1 for AgvCls 100 resulted displaced to higher wavenumber (1028 cm-1) for AgvCls 0. The bands
235
displayed at around 993 cm-1 does not present either increasing or decreasing tendency of band
236
intensities when the agavin composition diminished. This behavior may be possibly associated with an
237
spectral composite, where different absorbances overlap, enhance or subsume one another, making
238
difficult to assign peaks to specific vibration and then, identifying a tendency (Bureau et al., 2019). In
239
addition, an important change is detected in the BG 4; the band at 926 cm-1 displayed by AgvCls 100
240
decreased to disappearance with the reduction of % agavin in the solid mixture, which results in the
241
appearance of bands at 897 cm-1 by both AgvCls 10 and AgvCls 0, the corresponding-to-cellulose band
) as shown by AgvCls 0 (see Table 3). The BG 3 illustrates also the increasing of the band at 1053 cm-1
242
spectrum. The displacements of wavenumber showed by BG2 and BG4 possibly describes the change
243
from pentoses to hexoses in the composition of the polymeric framework of the mixture components.
244
The displayed spectra (Figure 3) illustrate, not only a comparative overlapped view of the spectra, which
245
allows to identify increasing, decreasing and displacements of absorption bands, but also the main
246
absorption peaks of agavins, which are squared and selected as functional group signals for further
247
analysis of commercial agavin samples.
248 249 250
Figure 3. Comparative visualization of spectra for agavin mixed with cellulose with different
251
composition. Band Group (BG) indicates evolution in specific wavenumbers and absorption intensity of
252
specific vibration bands.
253 254
3.3.2 Agavin – cocoa comparative analysis
255 256
A series of agavin-cocoa solid mixtures were analyzed to detect the change of band intensities and
257
displacements when composition of agavin decreases; the spectra are displayed in the Figure 4. The
258
assignment of the vibrational peaks corresponding to the FTIR analyzed samples are listed in Table A.1
259
(Supplementary information). The composition of cocoa in the agavin mixtures changes from 0% to
260
10% (agavin from 100% to 90%), as it can be observed by the colored lines corresponding to the
261
indicated mixture in the figure. The bands localized at the functional group frequency zone for AgvCca
262
90 shows a noticeable peak that merges at 1735 cm-1, as well as a band at around 1656 cm-1 got more
263
intense when the cellulose content in the mixture got increased. These bands are associated with
264
esterified carbonyls from pectic material (Redgwell, Trovato, & Curti, 2003), and with humidity in both
265
cocoa powder (Chung, Iiyama, & Han, 2003; Redgwell et al., 2003; Sotelo & Alvarez, 1991; Velázquez
266
de la cruz & Martín-Polo, 2000) and agavins (Kačuráková & Wilson, 2001). The vibration band at 1267
267
cm-1, displayed by AgvCca 90 corresponds to vibrations of C-H and C-O bonds (Bureau et al., 2019;
268
Lecumberri et al., 2007; Liendo, Padilla, & Quintana, 1997; Redgwell et al., 2003; Sotelo & Alvarez,
269
1991), and the band at 1253 cm-1 to N-H of proteinic material present in cocoa powder (Larkin, 2011).
270
With respect to the vibrational pattern at fingerprint region, the evolution of the band intensities
271
resemblances to the described in Figure 3. At 1158 cm-1 and around 1120 cm-1 wavenumbers, there are
272
increments in peak intensities showed by AgvCca 90, which also showed a displacement to a lower
273
wavenumber, from 1124 cm-1 to 1115 cm-1, with respect to the rest of AgvCca composites. Finally, the
274
band at 926 cm-1 for AgvCca 90 appears with a slight decrease in the absorbance intensity compared
275
with the rest of peaks; and at 869 cm-1, the bands did not exhibit an intensity change. The overlapped
276
spectra (Figure 4) allow to detect that shown spectra are very similar when the content of cocoa powder
277
changes from 0% up to 5%; nevertheless, the solid mixture with 10% of cocoa powder displayed
278
important variations in peak intensities at functional group frequency zone, unlike fingerprint region
279
where the intensity variations were minor.
280 281 282
Figure 4. Infrared spectra of different composites of agavin mixed with cocoa powder in a range of
283
100% to 90%.
284 285
A complementary analysis of the solid mixtures with higher differences in % composition of agavin-
286
cocoa was carried out with the purpose of describing the vibrational profile of composites. The spectra
287
are displayed in the Figure 5 and are respectively illustrated by different color lines. This schematization
288
exhibits an evolutive change of absorbance intensities and shifts of vibrational bands when the cocoa
289
component gets increased in the composite, in a higher degree than the showed in Figure 4, and even it
290
may be used eventually as calibration curve for analogous systems when a specific functional group is
291
selected, as reported previously (Espinosa-Velázquez et al., 2018).
292 293
The comparison among depicted samples in Figure 4 and 5 allows to identify that absorption signals
294
mainly undergo an augmentation in absorbance, as well as broad bands got split when the agavin
295
composition diminished in the different samples from 1800 cm-1 to 1015 cm-1; bands at lower
296
wavenumbers behaved in a decreasing manner. It is detectable the augmentation of the band at around
297
1740 cm-1 for AgvCca 80, from very weak to medium intensity, which even got split to the bands at
298
1743 cm-1, 1735 cm-1 and 1729 cm-1 for AgvCca 0. These bands are associated with esterified carbonyl
299
C=O group of fatty acids (Lecumberri et al., 2007; Liendo et al., 1997), acetylated carbonyls of pectic
300
material and ketones of antioxidant polyphenols present in the cocoa powder (Batista, de Andrade,
301
Ramos, Dias, & Schwan, 2016; Carrillo, Londoño-Londoño, & Gil, 2014; Lecumberri et al., 2007). The
302
broad and very weak band at 1643 cm-1 displayed for AgvCca 100 got increased and split in two bands
303
at 1653 cm-1 and 1623 cm-1 with medium intensity. These absorption peaks correspond to the stretching
304
of a C=O bond from an amide type I, N-H bending and C-C stretching of phenyl groups from
305
polyphenols present in cocoa powder (Batista et al., 2016; Carrillo et al., 2014; Larkin, 2011; Pretsch et
306
al., 2009). The bands at 1549 cm-1 and 1523 cm-1 for AgvCca 0, appeared and got increased from a very
307
broad and almost non-existent band at 1525 cm-1 for AgvCca 80 spectra, which is associated with the
308
symmetrical stretching of the atomic bonding system N-C=O that belong to amide type II and also the
309
N-H bending from protein content of the cocoa (Larkin, 2011; Redgwell et al., 2003; Sotelo & Alvarez,
310
1991). Absorption bands from lower wavenumbers than 1500 cm-1 down to 1280 cm-1 are mainly caused
311
by the presence of C-H bond from a variety of aliphatic and phenyl groups and by different vibration
312
types (see Table A.3 Supplementary material). The depicted bands at 1270 cm-1 and 1219 cm-1 by
313
AgvCca 100 evolved to a set of several absorption peaks showed by the AgvCca 0 sample. Vibrational
314
band group between 1280 – 1200 cm-1 region may be assigned to C-O stretching, O-H in-plane-bending
315
carbohydrates and C-H in-plane-bending for phenyls present in antioxidant and aliphatic hydrocarbon
316
compounds present in fatty acids of cocoa. A medium intensity absorption peak at 1248 cm-1 may be
317
associated with C-O-C and N-H stretching and belongs to acetylated carbonyls and amino acid groups
318
from pectic material, proteins, fatty acids and flavonoid ketones present in cocoa (Batista et al., 2016;
319
Carrillo et al., 2014; Lecumberri et al., 2007). The weak shoulder type peak at 1163 cm-1 for AgvCca
320
100 became split with the increment of cocoa content of the sample AgvCca 0, which are displayed as
321
medium size bands at 1176 cm-1 and 1150 cm-1. The band at 1123 cm-1 for AgvCca 100 was also split to
322
strong absorption peaks and shifted to 1105 cm-1, 1090 cm-1 and 1074 cm-1 for AgvCca 0. These split
323
bands correspond to C-O-C bonds of carbohydrate heterocyclic rings and glycosidic links associated
324
with insoluble fiber, which are also overlapped with some possible absorption peaks of the C-O-C bond
325
that belongs to the ester group of fatty acids present in the triacylglycerols of cocoa component
326
(Lecumberri et al., 2007). All spectra coincide with the stronger band at 1016 cm-1 that is assigned to C-
327
O-C bonds of intra and inter monosaccharide rings. The band at 930 cm-1 for AgvCca 100 diminished
328
almost to disappearance in AgvCca 0, with a reduction of agavin content. These bands at 1016 cm-1 and
329
932 cm-1 are associated with the spectral anomeric frequency region, which is defined by the symmetric
330
stretching vibrations of C-O-C glycosidic bonds of the polysaccharide framework (Cerna et al., 2003;
331
Chung et al., 2003; Nikonenko, Buslov, Sushko, & Zhbankov, 2005; Pretsch et al., 2009; Sekkal, Dincq,
332
Legrand, & Huvenne, 1995; Tipson, 1968). The medium size band at 930 cm-1 showed by AgvCca 100
333
decreased to a very weak shoulder type band at 922 cm-1 and got displaced to a lower wavenumber peak
334
displayed at 893 cm-1 by AgvCca 0, a similar band showed by cellulose in Figure 1 and Figure 3. This
335
evolutive band displacement from 930 cm-1 to 893 cm-1 wavenumbers coincides with the increasing of
336
insoluble dietary fiber associated with cellulose present in cocoa (Lecumberri et al., 2007).
337 338 339
Figure 5. Vibrational spectra of different composition of agavin mixed with cocoa powder in a range of
340
100% to 0%.
341 342
3.4 Vibrational analysis of commercial supplemented agavins
343 344
In order to analyze commercial supplemented agavin products, three agavins added with nutritive-value
345
ingredients were analyzed to identify their vibrational pattern, to compare them with composites
346
previously described herein and estimate composition. The commercial agavins are added with Aloe
347
vera, antioxidants (labeled as extract of green tea, cranberry, chamomile and vitamin D) and cocoa
348
(Thereobroma cocoa). The spectra of commercial products and agavin are depicted in Figure 6; agavin
349
standard is shown in the figure just for comparative goals. The assignment of the vibrational peaks
350
corresponding to the FTIR-ATR analyzed samples are listed in Table A.3 (supplementary material).
351
Bands around functional group frequency and fingerprint regions show absorption peaks with a high
352
similarity to the agavins´ (Figure 2). Nevertheless, particularities in specific bands are associated with
353
the nature of the supplemented ingredient. Regarding the functional group frequency zone, Metlin® Aloe
354
exhibited a very weak and broad pair of absorptions at 1640 cm-1 and 1570 cm-1, corresponding to
355
vibrations that belong to moisture, C=O stretching from uronic sugars and polyphenols; as well as the
356
band at 1570 cm-1 is associated with the carboxylate moiety (COO-) stretching (Chang, Chen, & Feng,
357
2011; Kiran & Rao, 2014; Okamura, Asai, Hine, & Yagi, 1996). Metlin® Antiox displayed also weak
358
and broad absorption peaks at 1682 cm-1, 1629 cm-1 and 1608 cm-1, which correspond to stretching of
359
C=O carbonyl from amides type I and N-H bending vibrations that belong to polyphenols supplied by
360
antioxidant supplement (Santos-Sánchez, Salas-Coronado, Villanueva-Cañongo, & Hernández-Carlos,
361
2019). Viv Agave® cocoa presents a similar spectrum displayed by the composite AgvCca 80 (Figure
362
5), whichalso displayed vibrational bands at 1737 cm-1 and 1651 cm-1. With respect to 1500 – 1200 cm-1
363
spectral zone, differences are basically described by the absorption intensity of peaks assigned to
364
aliphatic and aromatic C-H stretchings from carbohydrates of Aloe vera, pectic material from cocoa,
365
and also from polyphenols that are present in antioxidants(band assignation are shown in Table A.3 of
366
the supplementary material). The fingerprint zone of the samples displayed a low-size shoulder at 1157
367
cm-1 for Viv Agave® cocoa, which in common with the peak at 1107 cm-1 exhibit high resemblance to
368
the composite AgvCca60 (Figure 5); the intensity of these two absorption bands (around 0.3 Uabs for
369
band at 1157 cm-1 and 0.4 Uabs for band at 1107 cm-1) indicate that the proportion of cocoa powder in
370
Viv Agave® cocoa is in between AgvCca 80 and AgvCca 60 (20 and 40% of cocoa powder
371
composition). Absorption bands for Metlin® Aloe and Metlin® Antiox displayed high correlation, even
372
with agavin spectra when observing vibrational patterns in lower-wavenumber spectral zone.
373 374 375
Figure 6. Comparative scheme of spectra belonging to supplemented agavins Metlin® Aloe, Metline®
376
Antiox, Viv Agave® cocoa and Agavin.
377 378 379
4. Conclusions
380
The FTIR-ATR spectroscopy was used to analyze the spectra of standard carbohydrates and commercial
381
samples to identify characteristic peaks to explain their structural composition. A comparative analysis
382
of starch, inulin and cellulose with agave fructan (agavin) displayed particularities punctually described
383
for identification purposes at specific regions of the FTIR spectral window. The compilation of spectra
384
from different samples resulted an adequate method to identify changes in polysaccharide composition,
385
with individual spectra as well as with solid mixtures of standards. This schematization provides a
386
suitable manner to observe an evolutive behavior of the band intensities in accordance with the
387
concentration of the component, displaying the presence, absence, lengthening or weakening of specific
388
vibrational bands, as well as displacement of specific wavenumbers.
389
In this sense, the evaluation of the spectral fingerprint region allowed to describe absorption bands
390
susceptible to analyze the composition of artificial solid mixtures. The examination of agavin- cellulose
391
and agavin-cocoa systems resulted informative to observe change in band intensities and shifts, which
392
led to group peaks that may be even used for quantitative composition. Agavin-cellulose serial dilution
393
spectra showed stronger intensity peaks at around 1160 - 1105 cm-1 when the composition of agavin
394
decreased, and an opposite comportment with the absorption peak at 926 cm-1, where the band got
395
diminished with the reduction of agavin composition in the mixture. The system composed by agavin-
396
cocoa also showed similar behavior, with additional characteristic absorption bands that belongs to the
397
cocoa components, which helps to identify alterations of an agavin sample.
398
When a set of three commercial samples of supplemented agavins with Aloe vera, antioxidants and
399
cocoa powders were analyzed vibrationally, several signals were identified promptly considering
400
previous analyzed systems. Since the agavins were supplements with those mentioned specific type of
401
ingredients, based on their structure, the corresponding vibrational peak were readily identified. The
402
Aloe vera and antioxidant supplements did not alter the vibrational patter of the fingerprint region for
403
agavins, even the supplemented agavin with cocoa; just the vibration peak around 1160 cm-1 to 1107 cm-
404
1
405
spectroscopic analysis of agave solid mixtures is a valuable tool to procure information of food
406
ingredients for comparative goals with fructan-type commercial supplemented products, in order of
407
discriminate possible adulterations in related supplemented products.
zone displayed a slightly difference in the vibrational pattern for system analyzed. Finally, this
408 409 410 411
Acknowledgements
412
The first author thanks to CONACyT Mexico for the financial support of postdoctoral fellowship to the
413
first author. This report was partially financed and supported by the project SEP-PRODEP UCOL-
414
NPTC-250 (Mexico).
415 416
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Table 1. Types of agavin and supplemented commercial agavin suppliers. Entry
Commercial name
Supplier
Agavin A
Agave inulin
Ingredion. Monterrey, Nuevo Leon. Mexico.
Agavin B
Agave inulin
Vaserco Co. Zapopan, Jalisco, Mexico.
Agavin C
Agave inulin
Edulag. Villa Corona, Jalisco, Mexico.
Product A
Metlin® Aloe
BioTrendy Co. Zapopan, Jalisco. Mexico.
Product B
Metlin® Antioxidants
BioTrendy Co. Zapopan, Jalisco. Mexico.
Product C
Viv Agave® Cocoa
Vivagave Foods LLC. Mountlake Terrace, Washington, USA.
578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601
Table 2. Polysaccharide composition of powder mixtures Sample code
Agavin A
Cellulose
g
%
g
%
AgvCls 100
1.000
100
0.000
0
AgvCls 30
0.300
30
0.700
70
AgvCls 10
0.100
10
0.900
90
AgvCls 0
0.000
0
1.000
100
Agavin A
602 603 604 605 606 607 608 609 610 611 612 613 614 615 616
Cocoa powder
AgvCca 100
1.000
100.0
0.000
0.00
AgvCca 99.5
0.995
99.5
0.005
0.05
AgvCca 99
0.990
99.0
0.010
1.00
AgvCca 95
0.950
95.0
0.050
5.00
AgvCca 90
0.900
90.0
0.100
10.0
AgvCca 80
0.800
80.0
0.200
20.0
AgvCca 60
0.600
60.0
0.400
40.0
AgvCca 40
0.400
40.0
0.600
60.0
AgvCca 20
0.200
20.0
0.800
80.0
AgvCca 0
0.000
0.00
1.000
100.0
Table 3. Assignment of vibrational bands corresponding to the FTIR analyzed carbohydrate samples depicted in Figures 1, 2 and 3. Inulin
Starch
Cellulose
Agavin A
Agavin B
Agavin C
AgvCls100
AgvCls30
AgvCls10
AgvCls0
Bond Vibration
1640, vw
1643, vw
1643, vw
1643, vw
1642, vw
1643, vw
1643, vw
1639, vw
1637, vw
1640, vw
H-O-H st
1452, vw
1451, vw
1452, vw
1452, vw
1452
1452
1427, vw
1428, vw
1455, vw
1458, vw
C-H methyl oop bd; methylene, bd
1455, vw
C-H methyl oop bd; methylene, bd 1441, vw
1427, vw
1429, vw 1416, vw
1370, vw
1369, vw
1418, w
1420, w
1420, w
1420, w
1368, vw
1371, vw
1366, vw
1368, vw
1430, vw
1335, vw
1367, vw
1369, vw
1370, vw
1334, vw 1314, vw
1278, vw
1279, vw
1335, vw
1266, vw
1330, vw
1270, vw
1332, vw
1269, vw
1335, vw
1266, vw
1333, vw
1334, vw
1333, w
C-H methyl ip bd
1313, vw
1316, w
1316, w
C-H methyl ip bd
1278, vw
1280, vw
1282, vw
C-H methyl ip bd
1246, vw
C-O-H st; C-O-H ip bn
1241, vw
C-O-H st; C-O-H ip bn
1221, vw 1200, vw
1202, vw
1160, w 1144, m
1216, vw
1218, vw
1218, vw
1216, vw
1160, w sh
1157, vw sh
1158, vw sh
1160 vw sh
1122, w
1122, w
1124, w
1124, m
1203, vw 1159, w
1217, vw
C-O-H st; C-O-H ip bn
1201, vw
1201, vw
1202, vw
C-O-H st; C-O-H ip bn
1162, w
1160, w
1160, w
C-O-H, st; C-O-C st inter
1147, m
C-O-H, st; C-O-C st inter
1123, w 1104, m
1103, w
1103, m
1100, w
C-O-H, st; C-O-C st inter 1106, m
1105, m
1103, m
1051, s sh
1052, vs
1053, vs
C-O-H st; C-O-C intra oop st
1028, vs
1028, vs
1028, vs
C-O-H st; C-O-C intra oop st
997, vs sh
994, s sh
1076, m 1052, s sh
1040, s
1028, vs
1050, s sh
1050, s sh
1047, s sh
1047, s sh
1015, vs
1014, vs
1015, vs
1015, vs
986, s
990, s sh
930, w
879, vw sh
C-O-H st; C-O-C intra oop st
999, s sh 989, s sh
988, s sh
988, s sh
937, m
900, vw
926, m
927, m
926, m
987, s
C-O-C st intra, st inter C-O-C st intra, st inter C-O-C st intra, inter; C-O-H, st
926, m 897, w
871, vw
873, vw
873, vw
873, vw
C-O-C st intra, st inter
935, m
897, vw 859, vw
C-O-H, st; C-O-C st inter C-O-H st; C-O-C intra oop st
1054, s 1029, vs
995, vs
C-H methyl oop bd; methylene, bd C-H methyl oop bd; methylene, bd
1315, vw
1249, vw
C-H methyl oop bd; methylene, bd C-H methyl oop bd; methylene, bd; C-N st
1360, vw 1334, vw
C-H methyl oop bd; methylene, bd
873, vw sh
897, w
C-O-C st intra, inter; C-O-H, st C-O-C st intra, inter; C-O-H, st
Legends of bond types is as follows: st, stretching; bn, bending; ip, in-plane; oop, out-of-plane; s, symmetrical; as, asymmetrical; s, strong; vs, very strong; m, medium; w, weak; vw, very weak; sh, shoulder; blank, not observed; intra: cyclic ring; inter: exocyclic glycosidic bond. Bold letters represent atom bonding vibration.
Highlights • • • • •
FTIR-ATR spectroscopy is a rapid method to identify structure of polysaccharide samples. Vibrational spectra of ingredients may be used to identify adulterations in foods. Agavin and polysaccharides were characterized vibrationally to identify interest peaks. Absorption peaks assignments may be detected to find anomalies in solid mixtures. Commercial supplemented agavins displayed signals identified in the spectra of standards.
Conflict of interest declaration We, the authors, have no competing interests to declare.
Author Statement Oscar F. Vázquez-Vuelvas: Conceptualization, Methodology, Formal analysis, Writing – Original Draft, Writing - Review & Editing, Visualization. Félix A. Chávez-Camacho: Investigation, Data curation, Validation, Software. Jorge A. Meza-Velázquez: Resources, Formal Analysis, Writing - Review & Editing.
Emilio Mendez-Merino: Resources,
Formal Analysis, Writing - Review & Editing. Merab M. Ríos-Licea: Resources, Formal Analysis,
Writing
-
Review
&
Editing.
Juan
Carlos
Contreras-Esquivel:
Conceptualization, Methodology, Formal analysis, Resources, Writing - Review & Editing, Visualization, Project administration.