Recovery of polyphenols from the by-products of plant food processing and application as valuable food ingredients

    Recovery of Polyphenols from the By-products of Plant Food Processing and Application as Valuable Food Ingredients Dietmar R. Kammerer, Judith Kammerer, Regine Valet, Reinhold Carle PII: DOI: Reference:

S0963-9969(14)00404-9 doi: 10.1016/j.foodres.2014.06.012 FRIN 5330

To appear in:

Food Research International

Received date: Revised date: Accepted date:

10 March 2014 1 June 2014 4 June 2014

Please cite this article as: Kammerer, D.R., Kammerer, J., Valet, R. & Carle, R., Recovery of Polyphenols from the By-products of Plant Food Processing and Application as Valuable Food Ingredients, Food Research International (2014), doi: 10.1016/j.foodres.2014.06.012

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ACCEPTED MANUSCRIPT Recovery of Polyphenols from the By-products of Plant Food

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Processing and Application as Valuable Food Ingredients

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Dietmar R. Kammerer1,2*, Judith Kammerer1,3, Regine Valet1, Reinhold Carle1

1

Hohenheim University, Institute of Food Science and Biotechnology

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Chair Plant Foodstuff Technology, Garbenstraße 25, 70599 Stuttgart, Germany 2

Present address: WALA Heilmittel GmbH, Department of Analytical Development &

Research, Section Phytochemical Research, Dorfstraße 1, 73087 Bad Boll/Eckwälden,

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Germany

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Present address: lege artis Pharma GmbH + Co. KG, Breitwasenring 1,

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72135 Dettenhausen, Germany

*Corresponding author. Tel.: +49 7164 / 930-6688 Fax: +49 7164 / 930-7080 E-mail address: [email protected]

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ACCEPTED MANUSCRIPT Abstract Residues from plant food processing are valuable sources for the recovery of polyphenols, pectins, and proteins. These compounds may be used as natural antioxidants and functional food ingredients. The present review exemplifies innovative strategies for the valorization of

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by-products originating from apple, grape and sunflower processing. Apple pomace is an

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important starting material for pectin extraction. The color of apple pomace and of the pectins recovered therefrom is caused by oxidative browning of phenolic compounds. This limits the

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use of apple pectins as food gelling agents in very light-colored products. Consequently, a patented process for the simultaneous recovery of pectin and phenolic compounds from apple pomace has been developed. Phlorizin, the most abundant phenolic compound in apple pomace extracts, is the basic structure of a new class of oral antidiabetic drugs. Type 2

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diabetes mellitus may be treated by the inhibition of Sodium-Glucose Co-Transporter-2 (SGLT 2). In a recently patented process, dihydrochalcones are enriched and purified from undesired ortho-dihydroxy phenol compounds being prone to oxidation and covalent binding

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to proteins.

While pigments from apple pomace are obtained by enzymatic oxidation of phloridzin using fungal polyphenoloxidases, anthocyanin-based pigments may be extracted from grape skins

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without using sulfite applying a novel enzyme-assisted process. Consequently, anthocyanins

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and phlorizin oxidation products are valuable alternatives for the replacement of synthetic azo dyes, some of which have been associated with health risks.

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De-oiled sunflower press cake is a promising source of food protein as an alternative to soy and egg protein being devoid of toxic substances and low in antinutrients. Conventional alkaline protein extraction yields dark-colored products having reduced nutritional and functional quality. Therefore, a novel process for the production of light-colored sunflower

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protein isolates has been developed, combining mild-acidic protein extraction with subsequent adsorptive removal of phenolic compounds.

Keywords Adsorption, Apple Pomace, Grape Pomace, Phlorizin, Polyphenols, Sunflower Expeller

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ACCEPTED MANUSCRIPT 1. Introduction In contrast to tropical and subtropical fruits, those from the temperate zone are characterized by a large edible portion, while the proportion of waste accruing from fruit processing is

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relatively low. Nevertheless, total waste arising from apple juice processing and winemaking

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accumulates to huge amounts, thus being a valuable source of waste valorization. Solely in Germany, 200,000-250,000 tons of wet apple pomace is available per year. According to

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literature reports, total mass of grape pomace resulting from European wine production was estimated to vary between 5 and 14.5 million tons (Meyer et al., 1998; Schieber et al., 2001b; Torres & Bobet, 2001; Torres et al., 2002). Similarly, sunflower expeller resulting from oil extraction is abundant, since sunflower is one of the four most important annual crops grown

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for edible oil production. Its annual world production amounted to 37.4 million tons in 2012 (The Statistics Division of the Food and Agriculture Organization of the United Nations;

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FAOSTAT). Sunflower meal obtained from the press cake is so far mostly used as animal feed. It contains up to 4% of polyphenols being considered as anti-nutritive in animal nutrition. In addition, due to rapid polyphenol oxidation and their concomitant interactions

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with proteins under alkaline condition, the conventional extraction of sunflower proteins from

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the press cake is still challenging (Weisz et al., 2010; 2013). Polyphenols are unevenly distributed in plant tissues, and processing may result in the

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separation of those parts of the fruit and grain being particularly rich in polyphenols. This holds true for apple, grape, cereals and oilseeds, where UV absorbing flavonoids and phenolic acids, attractant anthocyanins and deterrent tannins are mainly deposited in the outer layers of the skin, aleurone cells, seed coats and hulls, respectively. On the other hand,

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the apple core and the seeds of apple and grape are rich in astringent polyphenols. Consequently, apple and grape pomace as well as sunflower hulls containing the core, skin and pips, and pigmented seed hulls represent rich sources of polyphenols worth being exploited for the recovery of such components as natural food ingredients. Polyphenols are characterized by high structural diversity, and may be subdivided into two major groups, the flavonoids and non-flavonoid compounds. Flavonoids share a common C6-C3-C6 carbon skeleton comprising flavanones, flavan-3-ols, flavan-3,4-diols, flavones, flavonols, dihydroflavonols as well as chalcones, dihydrochalcones, and aurones. The nonflavonoids are represented by phenolic acids, such as gallic acid, protocatechuic acid, and cinnamic acid derivatives, stilbenes and lignans. Polyphenols are present in plant tissues either in non-glycosylated form or as glycosides and/or associated with various organic acids and/or complex polymerized molecules with high molecular weight such as tannins.

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ACCEPTED MANUSCRIPT Beginning with the first reports of the so-called “French paradox” (Renaud & De Lorgeril, 1992), interest in polyphenols has distinctly been boosted because of their putative health benefits (Schieber et al., 2001b). During the last two decades, polyphenols have been associated with a multitude of health beneficial effects possibly preventing damages and

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diseases caused by oxidative stress (Havsteen, 2002; Kammerer et al., 2007). Due to their widespread occurrence in fruits, vegetables, nuts, cereals, and oilseeds,

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phenolic compounds are an integral part of human nutrition. However, their dietary intake considerably varies depending on age, gender and nutritional habits (German National Nutrition Survey II, 2008). According to Scalbert & Williamson (2000) the daily per capita

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polyphenol intake amounts to an estimate of 1 g.

Since the consumers‟ interest in healthy food has significantly increased within the last few years, there is a steady trend towards the production of functional foods and functional food

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ingredients. Among other secondary plant metabolites, polyphenols are believed to contribute to the health protective effect of many food commodities. Therefore, they have even

been

named

“vitamins

of

the

21st

century”

(Stich,

2000).

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supplementation of foods with polyphenols recovered from waste materials accruing from

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fruit, vegetable, cereals and oilseed processing may be a valuable strategy to increase the dietary ingestion of such compounds.

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For an economic recovery of polyphenols sufficient availability of raw material is mandatory. As earlier stated, in the case of pomace from apple juice extraction and winemaking such byproducts are abundant. The same is true for sunflower press cake arising from oil extraction. Therefore, these by-products have been in the focus of our research aiming at sustainable

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food production. In the following, the recent developments in the field of recovery and application of polyphenols from wastes accruing from food processing are exemplified by our attempts of apple pomace, grape pomace and de-oiled sunflower meal valorization.

2. Exploitation of apple pomace as a valuable source of polyphenols and pectin The global apple (Malus domesticus Borkh.) production is steadily growing with an annual world production amounting to 76.1 million tons in 2011. Within the last 50 years (19612011), apple production area has almost been tripled reaching its maximum extension (6.3 million ha) in 1995; however, subsequently being reduced to 4.7 million ha corresponding to the latest records (FAOSTAT). According to recent estimates, 70-75% of the apple is freshly consumed, while only about 25-30% of the annual production is converted into value added products of which 65% are processed into juice, and the remaining quantity is sold as apple 4

ACCEPTED MANUSCRIPT cider, purées, jams, as well as dried and ready-to-use apple products (Joshi et al., 1991, Bhushan et al., 2008; Shalini & Gupta, 2010). Although most fruits from the temperate zone such as the apple are characterized by a high

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proportion (about 75%) of edible tissue, seeds, stems, and in some cases even apple peels

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accrue from apple processing into juices and other derived products. According to Bhushan et al. (2008), the left-over of juice processing, the so-called pomace, consists mainly of skin

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and flesh (95%), seeds (2-4%) and stems (1%). Global apple juice production was estimated at 1.4 million tons during 2004-2005 with China steadily capturing the top position in world apple and apple juice production. China contributes around 600,000 tons of juice, and a further raise of Chinese production going along with the growing local consumption is to be

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expected. In Germany, about 700,000 tons of apples are annually processed into juice (VdF, 2013). Therefore, roughly 200,000 to 250,000 tons of apple pomace arise from German

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apple juice processing (Endress, 2000), while pomace generation from Japanese, Iranian, US-American, Spanish and New Zealand apple processing was reported to amount to 160, 97, 27 and 20 thousand tons for each of the latter countries, respectively (Bhushan et al.,

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2008; Gullón et al., 2007; Takahashi & Mori, 2006; Roberts et al., 2004; Lu & Foo, 1998).

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However, data concerning apple pomace availability are rather conflicting. According to other sources, taking into account the Brazilian, Chinese, and Indian production amounting to 0.8, 1 and 1 million tons of pomace (Vendruscolo et al., 2008; Wang et al., 2010; Shalini & Gupta,

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2010), the overall global availability of apple pomace may exceed 3,600,000 tons. The numerous ways of apple pomace utilization have recently been reviewed by various authors (Kennedy et al., 1999; Bhushan et al., 2008; Shalini & Gupta, 2010). Hitherto, apple

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pomace has mostly been disposed and used as a ruminant feed. This is mainly due to the high water content (>70%) and thus, the high susceptibility of the wet waste material toward microbial degradation. Unless immediately dried, apple pomace suffers from brown discoloration due to retained polyphenol oxidase (PPO) activities, and microbial spoilage. Unlike pectin from industrial mango peels, rapid depolymerization and de-esterification of apple pectins catalyzed by genuine and microbial pectinolytic enzymes is inevitable (Sirisakulwat et al., 2010). Consequently, to enable pomace stabilization for its further valorization, fast dehydration of apple pomace is mandatory, thus requiring an industrial drying facility which is associated with high investments and energy demand. As previously demonstrated by Schieber et al. (2003), harsh heat treatment in three-stage drum dryers used for the industrial production of apple pomace did not affect the stability of apple polyphenols being mainly retained in the pomace. Although requiring expensive drying, pectin extraction is still considered to be the most efficient way of apple pomace valorization 5

ACCEPTED MANUSCRIPT (Fox et al., 1991; Endress, 2000). To improve apple pectin color by removing the polyphenols from the product stream, an innovative process for the recovery of pectin and phenolic compounds has been developed (Schieber et al., 2003). The latter may serve as a natural counterpart to synthetic antioxidants and as a source of phlorizin (Kammerer et al.,

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2010; 2011; Bhushan et al., 2008). The de-pectinized residues from pectin extraction are still

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a source of fibres, and may be further used for food and non-food applications (Endress,

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1991). Apart from pectin and low molecular polyphenols, pomace still contains a multitude of valuable compounds such as malic acid, saccharides (fructose, glucose, and sorbitol), cuticular waxes, and the seeds. The latter are rich in highly unsaturated fatty oil, carotenoids and tocopherols, and high molecular weight condensed polyphenolics, and yellow pigments

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(Fromm et al., 2012a;b; 2013).

In the following, the most recent developments considering the simultaneous recovery of

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pectin and polyphenols including yellow-colored pigments, seed oil and saccharides suitable for their use as natural sweeteners are summarized aiming at the complete exploitation of

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apple pomace.

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2.1. Simultaneous recovery of pectin and polyphenols from apple pomace

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To meet the world‟s growing demand, global pectin production has been significantly augmented from merely 30,000 tons in 1995 to more than 45,000 tons in 2005 with apple pectin accounting for about 20% of total pectin production. While industrial apple pectin extraction has so far been limited to Europe, mainly Germany, France, Switzerland, and

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Poland, in 2003, a Chinese supplier conquered the apple pectin market, and Ukraine is expected as another new entrant. Pectin prices are mostly governed by apple pomace availability, and the degree of esterification (DE) of the extracted pectins. While the DE of genuine apple pectin is generally about 80% resulting in 10% higher prices, low esterified pectins not requiring total solid contents >60% for gelation are higher priced due to the recent trend towards low caloric jams and replacement of sugars by sweetening agents. Apple pomace availability has been threatened due to commonly applied enzymatic apple mash maceration aiming at increased juice yield and even so far unauthorized total liquefaction of the fruit. However, the commercial launch of pectinmethyl esterase (PME) preparations allowed the simultaneous increase of juice yields and retention of high molecular apple pectins, thus making the pomace resulting from mash maceration a valuable source of higher-priced low esterified pectin extraction. In contrast to light-colored citrus pectins, which may even be applied for producing transparent gels, brownish color of apple pectins restrict 6

ACCEPTED MANUSCRIPT their universal application. Therefore, the removal of polyphenols from the extracted pectin has been suggested (Carle et al., 2001). For this purpose, the acidic pomace extract (pH 2.8; 3.1 °Brix) was pre-heated to improve

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polyphenol adsorption onto the adsorbent resin consisting of a food-grade styrene-

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divinylbenzene co-polymerisate. Subsequently, the pectin-containing effluent was collected, and residual pectins were washed from the adsorber column until pectin was no more

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detectable in the eluate by alcohol precipitation. Phenolic compounds were recovered by their subsequent elution from the resin using methanol as the eluent. Purity and gelling properties of the resulting pectin were slightly increased, while its color appearance was significantly improved as shown by changing color parameters (L*a*b* values). This process

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was easily integrated into industrial pectin production (Schieber et al., 2003), and polyphenols obtained after solvent evaporation and lyophilization were determined according

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to Schieber et al. (2001a).

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2.2. Apple polyphenols

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Apple pomace including the seeds has been reported to be a rich source of polyphenols (Lu & Foo, 1997; Foo & Lu, 1999; Schieber et al., 2001b). The brownish color of apple pomace

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and pectins extracted therefrom is due to their enzymatic oxidation. Consequently, rapid PPO inactivation to inhibit browning is mandatory to obtain light-colored products. Alternatively, alkaline peroxide treatment has been proposed to bleach apple pomace for obtaining light-colored pectins thereof; however, this resulted in the degradation of pectins,

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and substantial loss of polyphenols (Renard et al., 1996). Flavonoids and

polyphenolic acids are

the predominant

polyphenols of

apples.

Anthocyanins, dihydrochalcones, flavanols and flavonols are the major representatives of the first. While hydroxybenzoic acids are rarely found in the fruit, hydroxycinnamic acid derivatives are abundant (Schieber et al., 2001a). Among them, 5-O-caffeoylquinic acid (syn. chlorogenic acid) is predominant, followed by p-coumaroylquinic acid and p-coumaroyl glucose (Pérez-Ilzarbe et al., 1991; Schieber et al., 2001a). Apple flavonoids include flavanols and their oligomers, with epicatechin and catechin being the major representatives. Additionally, catechin dimers such as procyanidin B1 and B2 have been identified in apple (Escarpa & González, 1998) together with higher polymerized procyanidins (Foo & Lu, 1999; Guyot et al., 2001). Flavonols are the most important subclass of apple flavonoids mainly represented by quercetin (Schieber et al., 2002a) and isorhamnetin glycosides (Schieber et al., 2002b). Although both red-fleshed and red-peeled 7

ACCEPTED MANUSCRIPT apple cultivars contain significant amounts of anthocyanins, predominantly cyanidin-3galactoside (Mazza & Velioglu, 1992; Vrhosek et al., 2004; Wu & Prior, 2005; Sadilová et al., 2006), these pigments have not been identified in commercially dried apple pomace, supposedly, due to their oxidative degradation during pomace handling and drying (Schieber

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et al., 2003).

For apple polyphenols, mainly procyanidins, quercetin derivatives and anthocyanins, strong

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antioxidant activities have been shown in vitro (Lu & Foo, 2000; Sadilová et al., 2006). Furthermore, numerous health beneficial effects of apple polyphenols have been reported (see Chapter 2.3). Consequently, apple pomace is considered a rich source of polyphenols which may be used as functional food ingredients and as natural antioxidants to replace their

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synthetic counterparts. In addition, apple polyphenols and specific compounds such as phlorizin derivatives extracted therefrom may be used as dietary supplements or even as

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plant derived drugs. Consequently, the process for the recovery of pectin and apple polyphenols has been investigated regarding the polyphenol pattern and yield from commercially dried apple pomace (Carle et al., 2001; Schieber et al., 2003). As can be seen

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from Table 1, the prevailing phenolic compounds detected in the lyophilized pomace extract

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were phlorizin, chlorogenic acid and a number of quercetin glycosides with quercetin 3galactoside being the predominant flavonol. Apple pomace extracts may be used as an antioxidant, e. g. to replace synthetic antioxidants and rosemary extracts exerting undesired

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flavor. According to a study by Arelt et al. (2002), the addition of 1-2 g/kg sufficed to inhibit rancidity of pizza salami during 8 weeks storage at -18 °C. Contrary to the un-deodorized rosemary extract, sensory evaluation revealed the admixture of apple polyphenols to be

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unperceivable.

2.3. Pharmacological effects of phlorizin and preparation of dihydrochalcone-enriched apple polyphenol extracts Among the phenolics which may be recovered from the by-products of apple juice processing by resin adsorption as reported in 2.1, dihydrochalcones, and especially phlorizin within this phenolic subclass, appear to be highly promising biofunctional compounds. For this reason, focus has been put on phlorizin in the following, emphasizing its potential as a health beneficial compound in human nutrition and disclosing its possible pharmaceutical applications. These are of particular interest, since its properties go far beyond conventional and indirect antioxidant activities or chemo-preventive effects, which are common to most phenolic compounds (Stevenson & Hurst, 2007).

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ACCEPTED MANUSCRIPT Phlorizin and corresponding dihydrochalcones are characteristic apple polyphenols. Phlorizin concentrations were shown to depend on the apple variety ranging from 3.05 to 303.3 mg/kg dry matter (Wojdylo et al., 2008). Furthermore, phlorizin is unevenly distributed within apple fruit tissues with contents ranging from 12 to 418 mg/kg and 4 to 20 mg/kg in the skin and

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flesh, respectively. In contrast, seeds have been demonstrated to be particularly rich sources

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of phlorizin with contents of 3,256-22,352 mg/kg defatted dry matter (Ehrenkranz et al., 2005;

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Fromm et al., 2012b).

Phlorizin was first isolated in 1835 by de Koninck (de Koninck, 1835) from the bark of apple trees. Based on the knowledge at that time, the bitter principle of phlorizin was classified as a substance suitable for the treatment of infectious diseases, fevers and malaria. Later

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scientific observations by von Mehring in 1886 (Schenk, 1921) demonstrated high oral concentrations of phlorizin to cause renal glucosuria, whereas chronic administration causes

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polyuria, polydipsia and weight loss, thus resembling the symptoms of diabetes, however, without the negative effects of hypoglycaemia. Hence, phlorizin has become a useful tool for studying renal function, and it has been proven that phlorizin can be safely administered

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intravenously to humans. In the 1950s, studies focused on the mechanisms of action of

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phlorizin on a cellular and molecular level revealing that phlorizin inhibits glucose transport in the kidneys and the small intestine. Continued research proved a transport system to be responsible for renal reabsorption of glucose which is located on the luminal membrane of

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proximal tubular cells. These studies also revealed the binding affinity of phlorizin to the renal glucose transporter to be 1,000 to 3,000 times higher than that of glucose (Ehrenkranz et al., 2005; Idris & Donnelly, 2009; White, 2010).

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Furthermore, phlorizin has been associated with glucose induced desensitization in diabetes (glucose toxicity) with this phenomenon being based on the fact that hyperglycemia per se leads to insulin resistance. It was also shown to normalize insulin sensitivity by lowering blood sugar levels (Ehrenkranz et al., 2005).

2.3.1. Effects of phlorizin on glucose transport systems Due to the polar character of glucose, a transport system is required to overcome the lipidrich cell membranes. In this context, two different membrane-associated carrier proteins for glucose transport have been described. The sodium glucose co-transporter type 2 (SGLT2) is one representative of a larger group of sodium substrate co-transporters occurring in different tissues such as epithelia, the central nervous system, and skeletal muscles. These co-transporters (SGLTs) are responsible for 9

ACCEPTED MANUSCRIPT the active transport of sugars against a concentration gradient into cells, which is coupled simultaneously to sodium ion transport along a concentration gradient. The type 2 transporter is a high-capacity, low affinity transporter, which is expressed in the S1 segment of the proximal tubule. It is considered to be responsible for the major part of renal glucose

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reabsorption (90% of filtered glucose) and transports one molecule of glucose per sodium

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ion. In contrast, type 1 of the sodium-glucose co-transporters is a high-affinity, low capacity

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glucose/galactose transporter exhibiting a 10-fold greater affinity towards galactose, and transports two molecules of glucose per sodium ion. It is primarily expressed in the small intestine but also in the S3 segment of the proximal tubule and the heart, where its expression regulates cardiac glucose transport. In contrast to the SGLT2 co-transporter its

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contribution to renal reabsorption is low (10%) (Jabbour & Goldstein, 2008; Idris & Donnelly, 2009; White, 2010).

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Another transport system is based on facilitated diffusion realized by glucose transporter proteins (GLUTs), each of them exhibiting different substrate specificity, kinetic properties and tissue expression profiles (Idris & Donnelly, 2009). GLUT4 is an insulin-mediated

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glucose transporter involved in glucose uptake in muscle and adipose tissues. GLUT1 and

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GLUT2 are insulin-independent glucose transporters, with GLUT1 being expressed in different tissues, such as erythrocytes, endothelial cells and in the late proximal tubule, whereas GLUT2 is expressed in the early proximal tubule. During renal reabsorption these

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GLUTs are responsible for glucose transport through the basolateral membrane and back into the peritubular capillaries (Idris & Donnelly, 2009; White, 2010). During food digestion glucose is absorbed via SGLT1 located in the small intestine. The

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circulating blood is continuously filtered in the glomeruli of the kidneys, where glucose is reabsorbed in the renal proximal tubules via SGLT2, and to a lower extent via SGLT1 (Jabbour & Goldstein, 2008) as well as GLUT1 and 2 (see above). Based on their physiological action within absorption in the small intestine as well as their renal reabsorption of glucose, both SGLT1 and SGLT2 are highly interesting from a pharmacological point of view. On the one hand, the former provides the opportunity to regulate glucose absorption via the inhibition of SGLT1, on the other hand, enhanced excretion of glucose via the suppression of renal glucose reabsorption by inhibition of SGLT2 is conceivable (Jabbour & Goldstein, 2008). With regard to glucose transport and absorption, the pharmacological potential of phlorizin can only partly be exploited for therapeutic purposes, because of its poor oral bioavailability. Phlorizin is readily hydrolyzed by lactase-phlorizin hydrolase yielding glucose and its aglycon phloretin. The latter does not affect SGLTs but blocks GLUT1/2. This hydrolysis occurs in the 10

ACCEPTED MANUSCRIPT small intestine, and phlorizin is only poorly absorbed in non-hydrolyzed form in the small intestine (Jabbour & Goldstein, 2008; Idris & Donnelly, 2009; Ehrenkranz et al., 2005; Walle & Walle, 2003). Phlorizin itself effectively inhibits SGLT1 and SGLT2 (White, 2010), thus acting as a potent anti-diabetes and weight-management agent. Concerns have arisen, that

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the glycosuric effect of SGLT2 inhibitors may increase the likelihood of developing urinary

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tract infections (UTI). However, further studies have demonstrated that these concerns were

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not justified (Jabbour & Goldstein, 2008).

In addition, phlorizin appears to be a prototype molecule used as starting point for numerous chemical modifications to obtain selective SGLT2 inhibitors. Such derivatives can be used as a novel therapeutic option for hyperglycaemia and/or obesity in patients with type 1 or type 2

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diabetes without requiring insulin. Thus, carbocyclic-O-glycosides (sergliflozin, T-1095, compound 45), heterocyclic-O-glycosides (remogliflozin, compound 46), carbocyclic-C-

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glycosides (dapagliflozin, compound 29), heterocyclic-C-glycosides (tofogliflozin) have been synthesized, with some of them exhibiting modified glucose moieties, and all of them revealing strong SGLT2 inhibition (Jabbour & Goldstein, 2008; Idris & Donnelly, 2009;

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Ohtake et al., 2012).

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Despite the aforementioned poor oral bioavailability, phlorizin has unique pharmacological properties, such as its ability to reverse glucotoxicity, to lower blood glucose levels without

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weight gain and the risk of associated hypoglycaemia, and to block intestinal glucose absorption and renal glucose reabsorption going along with weight loss. Further, its administration to humans has been regarded as safe. Since it forms part of the human diet, its application as a natural weight reducing and anti-diabetes agent appears particularly

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promising (Jabbour & Goldstein, 2008; Ehrenkranz et al., 2005).

2.3.2. Preparation of phlorizin enriched phenolic extracts Consequently, research efforts have been devoted to the establishment of processes for the selective enrichment of this dihydrochalcone, thus yielding apple-derived phlorizin preparations, which may be applied for the aforementioned purposes. Indeed, such products with standardized total polyphenol and phlorizin contents are currently being marketed as natural weight management food supplements, which are claimed to have positive effects on blood glucose levels. As an example of a process providing such preparations, a strategy has been developed aiming at the selective enrichment of dihydrochalcones, especially phlorizin, from extracts which may be obtained from the combined recovery of pectin and apple polyphenols from 11

ACCEPTED MANUSCRIPT apple pomace (see Chapter 2.1.). Previous attempts to obtain phlorizin enriched apple extracts were based on multiple extraction steps usually requiring further expensive chromatographic separation or selective enzymatic conversion of undesired co-extracted phenolic compounds exhibiting ortho-dihydroxy structures, such as quercetin or caffeic acid

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and their corresponding derivatives using laccase activities (Will et al., 2007; Ehrenkranz,

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2007). The latter approach further required chromatographic purification and adsorptive

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enrichment of the resulting enzyme treated extract. Consequently, both strategies are time consuming and cost intensive, and thus difficult to implement on an industrial scale. To yield sufficient amounts of preparations with high phlorizin contents, which are expected to be required due to the aforementioned beneficial pharmacological properties, a novel

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process was developed characterized by a much simpler purification procedure as compared to the previously described strategies. This process aimed at providing a dihydrochalcone

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preparation low in ortho-dihydroxy compounds, being stable against oxidation going along with unwanted browning as a result of polymerization of oxidized phenolic compounds. For this purpose, a crude apple polyphenol extract was prepared making use of water as

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extraction solvent or of further solvents, such as hydroalcoholic solutions. Such crude

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extracts may be purified prior to further treatment to reduce the amount of non-phenolic compounds. Subsequently, the resulting solution was alkalinized by adding sodium

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hydroxide solution, because ortho-dihydroxy phenolic compounds are prone to spontaneous oxidation under alkaline conditions. This oxidation was enhanced by aeration of the solution, whereas monohydroxy phenolic compounds such as phlorizin remained unaffected by this treatment. The removal of oxidized phenolics was further realized by adding a protein (e. g.

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gelatin) which is positively charged at the pH value of the oxidation solution, thus acting as a fining agent. At the end of the reaction, the pH value of the solution was adjusted to the pH of the isoelectric point of the protein resulting in the quantitative precipitation of the latter and removal of oxidized phenolics. Finally, insolubles were removed either by centrifugation or filtration. The resulting solution was further evaporated to remove organic solvents, and the aqueous phase may be converted into a stable product by spray drying or lyophilization (Boehlendorf et al., 2012). This straightforward procedure can easily be implemented into industrial process lines yielding high amounts of phlorizin preparations at low processing costs, thus providing the opportunity to apply such products as functional food supplements.

2.4. Natural colors based on apple polyphenols

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ACCEPTED MANUSCRIPT Since some synthetic azo-dyes including tartrazine so far commonly used for food coloring have been associated with attention deficit hyperactivity disorder (ADHD) (McCann et al., 2007), thus requiring a warning according to EU food regulations, their replacement by

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natural pigments is of increasing industrial relevance.

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Whereas apple polyphenols carrying vicinal hydroxyl functions are readily oxidized to reddish-brown polymeric compounds, oxidation of dihydrochalcones such as phlorizin brings

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about yellowish products which are assumed to be responsible for the typical color of cider and apple juices (Durkee & Poapst, 1965). The formation of such phlorizin oxidation products (POP) has been subject of various studies, and a dimeric oxidation product of phlorizin has been suggested (Goodenough et al., 1983; Oszmianski & Lee, 1991; Sarapuu & Kheinaru,

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1969). However, structure elucidation of a colorless intermediate (POPi) and its yellow derivative (POPj) (Figure 1), respectively, was only recently achieved by French scientists,

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confirming the dimeric nature of the water-soluble pigment which was obtained in a threestage process by enzymatic oxidation (Le Guernevé et al., 2004; Sanoner et al., 2005). Later, the kinetics of POPj formation as well as its color properties and color stability,

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respectively, depending on pH have been described by Guyot et al. (2007). Maximum

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pigment yield (84%) was obtained after 47 h of enzymatic oxidation with the colorless precursor being its major impurity. They proposed this yellow pigment as a natural alternative to tartrazine producing bright yellow color at pH < 5 and orange to reddish hues at pH > 6,

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and as a substitute of curcumin which is poorly soluble in water. Since the aforementioned pigment formation has been produced with pure chemicals, Fromm et al. (2013) demonstrated that POPj may be easily produced by enzymatic oxidation of more complex

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apple seed extracts using a mushroom PPO (polyphenoloxidase). Analogously, phloretin 2‟O-xyloglucoside was also converted into a yellow pigment reaching its maximum concentration after 27 h. Compared to a phlorizin model solution, extracts from apple seeds were shown to produce even higher color saturation and color brilliance than pure phlorizin solutions, thus demonstrating apple seed extracts to be a valuable source of natural pigments. However, its application as a natural food colorant still needs to be approved according to the EU directives 94/36 and 1333/2008.

3. Exploitation of grape pomace as a valuable source of phenolic colorants and antioxidants Apart from apples, grapes belong to the most important fruit crops with an annual world production quantity of around 69 million tons in 2011, being nearly equivalent to that of oranges (FAOSTAT). Grapes may be processed into a variety of common food products, 13

ACCEPTED MANUSCRIPT such as grape juice, jams, raisins and wine, with the latter predominating by far. Around 80% of the world grape production is estimated to be processed into wines resulting in the accumulation of great amounts of grape pomace (Kammerer et al., 2004; Mazza & Miniati, 1993). Statistical data regarding grape pomace amounts are lacking. Thus, data reported in

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literature may only be regarded as rough estimates, ranging from 5-7 million tons (Meyer et

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al., 1998) to 14.5 million tons solely in Europe (Torres & Bobet, 2001). However, given the

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aforementioned production quantities and considering must yields of around 80%, pomace amounts are safely assumed to exceed 10 million tons per year (Kammerer et al., 2004). Even though grape pomace offers the potential for recovering a wide range of high-value products, such as ethanol, tartrate, malate, citric acid, grape seed oil, hydrocolloids and

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dietary fibre, it has long been disposed of in the form of soil conditioner or for producing compost, since it is neither applicable in animal production due to poor digestibility.

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Furthermore, large amounts of pomace are accumulated within a comparatively short harvest period and, due to its high moisture content, this by-product is prone to rapid microbial spoilage. Consequently, grape pomace needs to be either processed immediately or transformed into stable dehydrated products (Rezaei & VanderGheynst, 2010). However, it

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must be kept in mind that the drying process and storage of the dried material go along with

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significant losses of valuable components, especially of phenolic compounds (Mishra et al., 2008; Tseng & Zhao, 2012).

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In recent decades, however, grape pomace has been recognized as a valuable source of phenolic compounds, which are poorly extracted from the skins and seeds upon vinification. Consequently, a great deal of attention has been devoted to the characterization of the

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phenolic profile and quantitation of total and individual phenolics in grape pomace. Firstly, these traits are determined by the grape variety, because fruits of different varieties are known to significantly differ in their profile and contents of phenolic components. These are further affected by vine pruning and training systems, phytosanitary conditions and maturity of the grapes, as well as cultivation and weather conditions. Secondly, process technology, i.e. vinification, markedly determines extraction yields of phenolic compounds and, thus, phenolic contents of the resulting grape pomace. Among others, the maceration technique, such as skin maceration vs. thermovinification, fermentation temperature, the application of pectinolytic enzymes for enhancing polyphenol release in the course of vinification, the maceration time, yeast type and pressing parameters are known to have an impact on polyphenol extraction from grapes (Kammerer & Carle, 2009; Sacchi et al., 2005). Thus, our studies to optimize polyphenol recovery from grape pomace started with a thorough investigation into the phenolic profile and contents of different pomace samples from red and white wine production. Up to 39 compounds were identified and quantitated in 14

ACCEPTED MANUSCRIPT the skins and seeds, revealing great heterogeneity between the samples. This screening demonstrated that the skins of deeply colored red grapes may still contain as much as 132 g of anthocyanins/kg dry matter after pressing of the grape mashes. Further, especially the seeds were rich in flavan 3-ols with contents ranging up to 18.76 g/kg dry matter. Large

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variabilities were observed, which concerned all individual phenolic compounds, depending

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on cultivar and vintage. The data confirmed that skins and seeds from pomace of most grape

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cultivars are a promising low-cost source of phenolic compounds, but also revealed that due to natural variability and differences in process technology thorough screening of the raw materials considered for polyphenol recovery is mandatory for establishing profitable polyphenol recovery processes (Kammerer et al., 2004).

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Grape seeds, which were shown to be particularly rich in flavan 3-ols, are also source of a high value edible oil. Consequently, we evaluated whether the press residues of seed oil

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production can still be used for recovering phenolic compounds. Total amounts of all compounds identified by HPLC-DAD-MSn ranged from 4.81 to 19.12 g/kg of defatted dry matter (DM) in integral grape seeds and from 2.80 to 13.76 g/kg defatted DM in the press

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residues obtained after mechanical oil recovery. Thus, the press residues of grape seed oil

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production are still rich in phenolic compounds and, consequently, grape seeds may be exploited both for the recovery of the seed oil and phenolic antioxidants (Maier et al., 2009b).

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Given the data on anthocyanin contents of grape pomace reported above it appears reasonable that the by-products of red wine production have long been used for recovering extracts suitable for food coloring (enocyanin, E 163). The exploitation of food processing byproducts in terms of the recovery of natural food pigments adds to sustainable agricultural

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production, but has also become of increasing relevance with the so-called Southampton study. The latter revealed a potential correlation between an increase of attention deficit hyperactivity disorder in children and the consumption of drinks with added azo dyes and benzoic acid (McCann et al., 2007). As a consequence, labelling of food colored with synthetic dyes with warning notices has become mandatory since July 2010, which resulted in a steadily increasing trend towards natural food colorants. In this context, enocyanins are a promising alternative, which have so far been recovered using sulfite-containing water or alcohols. Anthocyanins are transformed into sulfonic acid derivatives by applying sulfite, thus rendering the reaction products more hydrophilic than the anthocyanins themselves which translates into enhanced extraction yields. The sulfonic acid formation is a reversible reaction. Hence, sulfite can be removed from the resulting extracts releasing the anthocyanins. However, in practice, quantitative removal of sulfite from the extracts is impossible, which is crucial, since pseudoallergenic reactions caused by foods with added sulfites have been described, thus requiring labeling by European Community regulations. 15

ACCEPTED MANUSCRIPT Consequently, a novel process for the optimized polyphenol extraction from grape pomace has been developed, not only considering anthocyanins but also all other phenolic compounds of grape skins and seeds, and avoiding the use of sulfite. For this purpose, pectinolytic and cellulolytic enzyme preparations were applied for polyphenol extraction from

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the re-suspended grape pomace to degrade grape cell wall polysaccharides, thus enhancing

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the release of phenolic compounds from the grape matrix. The study showed that careful

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selection of enzymes and screening for the absence of pigment-degrading side activities of technical enzyme preparations is of particular relevance. The successful disintegration of the grape pomace cell wall matrix was measured based on the release of galacturonic acid from cell wall pectins and of glucose as a result of cellulase activity. In addition, the desired effect

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of enhanced polyphenol release was measured by HPLC-DAD. Pre-extraction of the pomace followed by re-suspension of the residue and enzymatic treatment with a combination of

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pectinases and cellulases resulted in even higher recovery rates. This can be explained by reduced inhibitory effects of polyphenols on enzymatic digestion, because phenolic compounds were partly extracted during the first step (Kammerer et al., 2005a). Enzymatic digestion of grape pomace was optimized with regard to pH value, temperature and enzyme

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dosage applied for extraction using a D-optimal experimental design. Maximum polyphenol

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yields were obtained when suspending grape pomace in water and pasteurizing prior to further treatment to inactivate deteriorative enzymes responsible for polyphenol degradation.

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The pomace was pre-extracted at 50 °C. In a subsequent step, enzymatic digestion of the cell wall matrix was performed for two hours at 40 °C and pH 4.0 using a mixture of pectinolytic and cellulolytic enzymes (ratio 2:1) at a dosage of 4,500 mg/kg dry matter. This procedure resulted in significantly improved polyphenol extraction yields reaching 91.9, 92.4,

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and 63.6% for phenolic acids, non-anthocyanin flavonoids and anthocyanins, respectively. The yields obtained were comparable to those from extractions applying sulfite. Consequently, enzyme-assisted polyphenol extraction may be considered a suitable alternative to the application of sulfite (Figure 2; Maier et al., 2008). The resulting extracts may be transformed into more stable products by drying. This can be achieved either by lyophilization or by spray drying with polysaccharides being added as carriers (Maier et al., 2009a). Further, phenolic compounds can conveniently be concentrated by means of food-grade adsorber resins. For this purpose, the anthocyanins of a red grape pomace extract were purified and concentrated using a styrene-divinylbenzene copolymer. The study revealed pigment losses during column loading and washing of the resin to remove undesired compounds to be negligible. Pigment elution from the adsorber column was achieved using methanol, ethanol and 2-propanol. Recovery rates were in the range from 96-100%, 86-96% and 78-88%, respectively, when using the aforementioned 16

ACCEPTED MANUSCRIPT alcohols for elution, demonstrating that anthocyanins may be recovered without appreciable losses using this technology. Advantageously, the alcoholic pigment eluates containing anthocyanins in concentrated form can easily be further concentrated under mild conditions

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(Kammerer et al., 2005b).

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Grape pomace extracts obtained according to the aforementioned processes may be used as functional components of enriched foods both to color the products with anthocyanins and

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to supplement with biofunctional plant metabolites. To assess the stability of color and of individual compounds upon processing and storage, model pectin and gelatin gels were prepared and supplemented with grape pomace extracts, which were obtained by enzymatic digestion of a red grape pomace and subsequent purification by resin adsorption, spray

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drying and lyophilization, respectively. Processing of the gels, i.e. thermal treatment had the most significant effect on total phenolic contents resulting in total losses up to 24.6%. Light

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considerably decreased the contents of phenolic compounds during storage, whereas the effect of storage temperature (6 °C vs. 20 °C) on their stability was less pronounced. In contrast to the contents of individual and total phenolics, antioxidant activity and color of the

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sample remained virtually unchanged or were only slightly decreased throughout the 24

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week storage period. Thus, the model gels still exhibited brilliant colors and strong antioxidant capacity even after storage of 24 weeks at ambient temperature, demonstrating

et al., 2009a).

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that grape pomace phenolics may be successfully applied to enrich processed foods (Maier

A number of further attempts aiming at efficient extraction of phenolics from grape pomace has been described in recent years, mostly based on sophisticated extraction set-ups,

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including among others dynamic superheated liquid extraction of phenolics (LuqueRodríguez et al., 2007), subcritical water / pressurized hot water / pressurized solvent extraction or semi-continuous hot-cold extraction (Aliakbarian et al., 2012; Monrad et al., 2012; Srinivas et al., 2011; Vergara-Salinas et al., 2013), supercritical fluid extraction (Pinelo et al., 2007), the application of high voltage electrical discharges (Boussetta et al., 2011), microwave-assisted extraction (Dang et al., 2013), and extraction assisted by pulsed ohmic heating (El Darra et al., 2013). The successful applicability of these technologies has mostly been demonstrated in laboratory experiments revealing promising polyphenol extraction yields. However, scaling-up of such methods will be challenging due to cost-intensive equipment and safety precautions which need to be considered. Thus, enzyme-assisted extraction of grape pomace appears particularly valuable since its feasibility at pilot scale has been successfully demonstrated and scale-up is a straightforward process requiring equipment already well-established in the wine industry. The resulting phenolic preparations may be applied as technofunctional ingredients for coloring foods or as natural antioxidants. 17

ACCEPTED MANUSCRIPT Further, grape extracts are increasingly applied for their putative health-beneficial effects. A wide range of biofunctional properties has been reported, among others antimutagenic and anticarcinogenic properties, antilipogenic effects, protective effects regarding cardiovascular diseases and antiageing activities (Yu & Ahmedna, 2013). However, it must be kept in mind

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that most of these effects of grape pomace phenolics have been studied in vitro and still

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need sound scientific evidence in vivo, especially given the fact that grape phenolics have

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been found to behave differently in in vitro and in vivo systems (Veskoukis et al., 2012).

4. Exploitation of residues from sunflower oil extraction as a valuable source of

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polyphenols and protein

Sunflower (Helianthus annuus L.) oil is one of the four most important oilseed crops. Its

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worldwide production steadily grew within the last three decades to reach a global production of 15.2 million tons in 2012 (FAOSTAT), and FAO forecasted world production of sunflower oil to amount to around 22.4 million tons towards 2050 (ASAGIR, 2012). About 90% of sunflower seed oil consists of unsaturated fatty acids. Since edible oils being rich in mono-

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unsaturated fatty acids are considered to be most healthy, modern high oleic sunflower

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breeds containing more than 80% of oleic acid are the nutritionally most valuable option, thus even exceeding the oleic acid content of olive oil (Damude & Kinney, 2008). The proportion

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of hull and kernel in sunflower seed varies considerably depending on cultivars. Usually, the oilseed type is composed of 20-30% hulls, whereas the seeds of non-oilseed varieties may consist of up to 47% shells. According to Gonzáles-Pérez & Vereijken (2007), the lipid contents of whole seeds and dehulled kernels range between 34-55 and 47-65% on dry

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weight basis, respectively.

Prior to the extraction of sunflower oil the seeds may be partially dehulled depending on the cultivar which is associated with a weight loss of about 10%, while excessive shelling results in loss of oil. For the oil extraction three basic methods are applied (FAO, 2010). The solvent extraction where the kernels are commonly flaked prior to hexane extraction results in a very efficient oil recovery with only 5-15 g oil retained in 1 kg of the extracted meal. In contrast, the residues resulting from mechanical pressing in a screw press, the so-called expeller still contains 50-60 g oil/kg. To combine almost exhaustive oil extraction with solvent-free processing, prepress solvent extraction comprising a screw pressing operation followed by solvent extraction is the most preferred method of sunflower oil recovery. The residual oil content of the de-oiled press cake obtained by combining both processes is below 3% (Pickardt et al., 2011).

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ACCEPTED MANUSCRIPT Sunflower seeds contain about 20% of protein, while protein contents of de-oiled expeller resulting from oil processing even range from 30 to 50% (Dorell & Vick, 1997). Although being a poor source of lysine, proteins extracted from sunflower press cake are considered a highly valuable food ingredient because of its otherwise well-balanced amino acid

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composition (Tkachuk & Irvine, 1969). In contrast to soy and wheat proteins, sunflower

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proteins are devoid of substances causing adverse reactions, and although sunflower seed is

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extensively used as a snack, in form of edible oil, in margarines, and in bread, only few clinical reports have indicated allergenic reactions towards sunflower constituents (Axelsson et al., 1994; Kelly & Hefle, 2000).

The total phenolic contents of sunflower seeds range from 30-42 mg/100 g dry matter for the

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dehulled kernels and from 0.4-0.9 mg/100 g for the corresponding shells. Monocaffeoyl quinic acids amount to 84-92% of total phenolics in kernels, further 6-15% dicaffeoyl quinic

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acids, 1-4% unesterified phenolic acids, and 0.4-1% coumaric and ferulic acid derivatives were found (Weisz et al., 2009). These data reveal defatted sunflower meal to be a promising source of phenolic compounds that might be recovered and used as natural

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antioxidants. The press residues originating from sunflower oil extraction are still rich in

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phenolics. Although sunflower proteins exhibit techno-functional properties which are similar to those of soy proteins, concepts for their isolation have not been successfully applied on industrial scale so far. This is mainly due to the high amount of polyphenols covalently linked

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to the proteins in their oxidized form, thus affecting protein functionality, as well as their discoloration, and low product yields. Aiming at sustainable food production, numerous attempts have been made to valorize the press residues arising from sunflower oil extraction

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without deleterious co-extraction and oxidative degradation of polyphenols (Gonzáles-Pérez et al., 2002). However, none of these processes has so far successfully been implemented into industrial sunflower processing. To circumvent the problems associated with alkaline sunflower protein extraction, a process based on isoelectric protein precipitation from mild-acidic extracts of de-oiled sunflower press cake has been developed and optimized in our laboratories (Pickardt et al., 2009; 2011) (Figure 3). This process was combined with an adsorptive discoloration of the sunflower protein extracts (Weisz et al., 2010; 2013). Food grade adsorbents as Amberlite XAD 16HP and FPX 66 showed optimal decoloration of the sunflower crude extracts. In contrast, ion exchange resins exerted maximal binding of monomeric phenolic compounds, but were less effective in removing higher molecular colored compounds. The combination of polyphenol removal by anion exchange and adsorption with subsequent washing of the precipitated proteins considerably improved the process efficiency compared to a single-step adsorption 19

ACCEPTED MANUSCRIPT process, resulting in a 99.4% reduction of monomeric phenolic compounds (Weisz et al., 2010). In a further process step the phenolic compounds can be recovered. Optimum conditions for

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an exhaustive desorption of the polyphenols from the adsorbent were elaborated (Weisz et

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al., 2013). As a result of adsorptive binding of polyphenols from the sunflower protein extract onto the resin and their subsequent desorption, the polyphenol contents of the eluate

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revealed a considerable enrichment of both monomeric and dimeric substances. Thus, sunflower polyphenols may be obtained in enriched form without tedious concentration of large volumes arising from the protein extraction process. The polyphenol-enriched eluate

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may be used as a natural antioxidant due to its high antioxidant activity.

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3. Conclusions

Directive 2008/98/EC (the so-called ´Waste Framework Directive´) implemented basic concepts for waste management based on a hierarchical system, where the most favored

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option is the avoidance of waste accruing from processing, followed by waste minimization,

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reuse and recycling of waste streams. The least favored options are energy recovery from waste materials, and finally, waste disposal. Furthermore, the a. m. EU directive sets rules

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applying the “polluter pays principle”, and defined two targets regarding waste recycling and recovery to be achieved by 2020. Namely 50% of waste materials arising from households and other origins similar to households shall be prepared for reuse, and 70% from demolition and construction be reused. However, waste materials defined in the list of wastes in

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category 170504 of the Commission Decision 2000/532/EC were still excluded, among them, wastes from agriculture, horticulture, aquaculture, forestry, hunting and fishing such as wastes from fruit, vegetable, cereals, edible oils, cocoa, coffee, tea and tobacco preparation and processing. Using apple juice processing as an example, avoidance of waste should be the most preferred solution which could be easily achieved by legalizing the use of hemicellulolytic and cellulolytic enzyme preparations for pomace and even mash liquefaction. Both measures would allow the exhaustive extraction of soluble solids by the complete degradation of the cell wall materials, thus raising juice yields from about 80 up to 95% (Schols et al., 1991; Will et al., 2000). However, apart from poor sensory acceptance of the juices due to extensive polyphenol extraction, applying apple liquefaction would result in almost complete pectin degradation, thus ebbing away the valuable source of apple pectin. Furthermore, other valuable by-products such as natural sweeteners, fibres and polyphenols recovered from the 20

ACCEPTED MANUSCRIPT pectin side-stream would be jeopardized. As exemplified by the delicate equilibrium of apple juice yield optimization and by-product exploitation, waste management requires holistic concepts considering the controversial views of waste avoidance and waste valorization. In the latter case, waste prevention would clearly go at the expense of valuable by-products

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obtained from the waste stream!

From the examples illustrated in this review the enormous potential of valorization of waste

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materials originating from agroindustry including wastes from bakery and confectionery, sugar processing, and the production of alcoholic and non-alcoholic beverages becomes obvious. For some waste materials, most troublingly, there is missing common policy regarding waste management. This holds particularly true for the liquid and solid wastes

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incurring with olive oil production which have created severe environmental harm throughout the Mediterranean regions. Consequently, it is imperative to develop sustainable solutions

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which should be forced by stricter environmental legislation.

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ACCEPTED MANUSCRIPT Boussetta, N., Vorobiev, E., Deloison, V., Pochez, E., Falcimaigne-Cordin, A., & Lanoisellé, J.-L. (2011). Valorisation of grape pomace by the extraction of phenolic antioxidants: application of high voltage electrical discharges. Food Chemistry, 128, 364-370.

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ACCEPTED MANUSCRIPT Escarpa, A., & González, M. (1998). High-performance liquid chromatography with diodearray detection for the determination of phenolic compounds in peel and pulp from different apple varieties. Journal of Chromatography A, 823, 331-337.

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Rubner-Institute,

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ACCEPTED MANUSCRIPT Gullón, B., Falqué, E., Alonso, J. L., & Parajó, J. C. (2007). Evaluation of apple pomace as a raw material for alternative applications in food industries. Food Technology and Biotechnology, 45, 426-433.

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procyanidins covering a large range of polymerization states. Journal of Agricultural and Food Chemistry, 49, 14-20.

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class of oral antidiabetic drug. Diabetes, Obesity and Metabolism, 11, 79-88. Jabbour, S. A., & Goldstein, B. J. (2008). Sodium glucose co-transporter 2 inhibitors:

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blocking renal tubular reabsorption of glucose to improve glycaemic control in patients with

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from red and white grape varieties (Vitis vinifera L.) by HPLC-DAD-MS/MS. Journal of Agricultural and Food Chemistry, 52, 4360-4367. Kammerer, D., Claus, A., Schieber, A., & Carle, R. (2005a). A novel process for the recovery of polyphenols from grape (Vitis vinifera L.) pomace. Journal of Food Science, 70, C157C163. Kammerer, D., Gajdos Kljusuric, J., Carle, R., & Schieber, A. (2005b). Recovery of anthocyanins from grape pomace extracts (Vitis vinifera L. cv. Cabernet Mitos) using a polymeric adsorber resin. European Food Research and Technology, 220, 431-437. Kammerer, D. R., Saleh, Z. S., Carle, R., & Stanley, R. A. (2007). Adsorptive recovery of phenolic compounds from apple juice. European Food Research and Technology, 224, 605613.

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ACCEPTED MANUSCRIPT Kammerer, D., & Carle, R. (2009). Evolution of polyphenols during vinification and wine storage. Functional Plant Science and Biotechnology, 3 (Special Issue 1), 46-59. Kammerer, J., Kammerer, D. R., Jensen, U., & Carle, R. (2010). Interaction of apple

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fractionation of major apple flavonoids, phenolic acids and dihydrochalcones using anion exchange resins. LWT - Food Science and Technology, 44, 1079-1087.

an IgE-binding protein. Allergy, 55, 556-559.

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Kelly, J. D., & Hefle, S. L. (2000). 2S methionine-rich protein (SSA) from sunflower seed is

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Figure 1

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Legends to Figures and Tables

Structures of the phlorizin oxidation products POPi and POPj (reprinted from

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Fromm et al., 2013; with kind permission from Elsevier)

Scheme of enzyme-assisted extraction of polyphenols from grape pomace

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Figure 2

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(reprinted from Maier et al., 2008; with kind permission from Springer Science

Figure 3

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Process based on isoelectric protein precipitation from mild-acidic extracts of de-oiled sunflower press cake combined with adsorptive discoloration of the

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sunflower protein extracts (Pickardt et al., 2009; 2011; Weisz et al., 2010; 2013)

Table 1

Main phenolic compounds in the lyophilisate of an apple pomace extract (reprinted from Schieber et al., 2003; with kind permission from Elsevier)

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ACCEPTED MANUSCRIPT Figure 1

COOH

COOH HO

O O

POPi OGlc

OGlc

OH

POPj

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OH

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OH

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Table 1

9.3

Procyanidin B2

9.3

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Epicatechin

Catechin

2.4

Chlorogenic acid

14.3

p-Coumaroylquinic acid1

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1.8

p-Coumaric acid

0.5 0.4

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Ferulic acid Quercetin 3-galactoside Quercetin 3-rhamnoside

Quercetin 3-rutinoside

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Quercetin 3-arabinoside

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Quercetin 3-xyloside

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Quercetin 3-glucoside

Phlorizin

Phloretin

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Phoretin xyloglucoside2 Quercetin

11.4 4.7 3.9 1.8 1.3 1.1 40.4 8.0 6.5 0.5

Total

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[mg/kg]

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Phenolic compound

117.6

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Calculated as p-coumaric acid; calculated as phlorizin; data are mean values of two replicate determinations

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Food processing by-products serve as rich sources of high-value phenolic compounds Combined Simultaneous recovery of pectin and polyphenols from apple pomace

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Isolation of phlorizin for dietary and pharmaceutical purposes

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Novel process for recovering phenolic colorants and antioxidants from grape pomace

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