Polyphenols of Traditional Apple Varieties in Interaction with Barley β-Glucan: A Study of the Adsorption Process

Characterization of the Effect of a Novel Production Technique for 'Not from Concentrate' Pear and Apple Juices on the Composition of Phenolic Compounds

The consumption of 'not-from-concentrate' (NFC) fruit juices can be a convenient and enjoyable way to incorporate the nutritional benefits and flavors of fruits into one's diet. This study will focus on the effect of production of juices from apple and pear fruits, by using centrifugal decanter and tangential filtration, on the profile of polyphenols as a valuable source of bioactive compounds. Likewise, by-products from the juice industry were characterized in order to understand the high-value-added potential based on their composition of polyphenols. Briefly, apple and apple juice showed great contents of chlorogenic acid (0.990 ± 0.021 mg/g of DW), the dihydrochalcone phloridzin (1.041 ± 0.062 mg/g of DW), procyanidins (0.733 ± 0.121 mg/g of DW) and quercetin derivatives (1.501 ± 0.192 mg/g of DW). Likewise, the most abundant compounds in pear and pear juices were chlorogenic acid (0.917 ± 0.021 mg/g of DW), caffeoylquinic acid (0.180 ± 0.029 mg/g of DW), procyanidins (0.255 ± 0.016 mg/g of DW) and quercetin derivatives (0.181 ± 0.004 mg/g of DW). Both temperature and tangential speed affect the amount of phenolic compounds in fruit juices, highlighting the need to control the technological process to obtain a more nutritious/healthier beverage. Overall, NFC juices arise as a better option when compared with concentrated juices. Furthermore, the higher yield of phenolic compounds found in fruit pomace clearly open new ways for upcycling this fruit by-product as a high-value-added ingredient.

Characterization of polyphenols compounds extracted from stressed apple peel and their interaction with β-lactoglobulin

This paper proposes to apply a postharvest environmental stress to red apples, Malus domestica, variety Red Delicious in order to increase the polyphenols compounds (PP) content in their peels. The possibility of enhancing extractable PP provides a useful alternative for the use of discarded crops in the food industry. A great increase in PP was observed in response to light damage produced by the environmental stress applied in this work. Flavonols > anthocyanins > flavanols > dihydrochalcones > phenolic acids is the order in PP content. The interaction of the extracted PP from unstressed and stressed apple peels with beta-lactoglobulin (β-LG) was characterized. A PP/β-LG complex which was formed with one single binding site in the protein was determined. The interaction was spontaneous and enthalpy driven. PP extracted from unstressed samples had greater affinity for the protein than PP extracted from stressed samples, possibly due to the polar characteristic of anthocyanins. The results of this last study could provide a better understanding of the interaction between PP and β-LG to incorporate them into functional foods.

Simulated Gastric and Intestinal Fluid Electrolyte Solutions as an Environment for the Adsorption of Apple Polyphenols onto β-Glucan

Interactions with dietary fibers in the gastrointestinal tract might affect the potential bioactivities of phenolic compounds. In this study, the interactions between apple phenolic compounds and β-glucan (a dietary fiber) were studied by studying the adsorption process in simulated gastric and intestinal fluid electrolyte solutions. Phenolic compounds were extracted from apples, adsorbed onto β-glucan (2 h, 37 °C, in gastric or intestinal fluid electrolyte solutions), and determined using high performance liquid chromatography. Phenolic compounds (flavan-3-ols, flavonols, phenolic acids, and dihydrochalcone) were stable in the gastric fluid (pH 3). In the intestinal fluid (pH 7), flavan-3-ols were not found and chlorogenic acid isomerized. Polyphenols from the apple peel (up to 182 and 897 mg g⁻¹) and flesh (up to 28 and 7 mg g⁻¹) were adsorbed onto β-glucan in the gastric and intestinal fluids, respectively. The adsorption was affected by the initial concentration of the polyphenols and β-glucan and by the environment (either gastric or intestinal fluid electrolyte solution). By increasing the initial polyphenol amount, the quantity of adsorbed polyphenols increased. Increasing the amount of β-glucan decreased the amount adsorbed. The results can be helpful in explaining the fate of phenolic compounds in the gastrointestinal tract.

Occurrence of Patulin and Polyphenol Profile of Croatian Traditional and Conventional Apple Cultivars during Storage

Apples and apple-based products are among the most consumed fruits around the world. However, they are susceptible to infection with the fungi Penicilium expansum. In addition to the reduction of apple quality, secondary metabolism of this fungus produces a mycotoxin patulin that has a negative effect on human health. Currently, there is no available research in the literature on the resistance of Croatian traditional apple cultivars to contamination with P. expansum, and consequently, on the patulin content in apples and apple juice produced from those apples. Although the mechanism of apple resistance to fungal diseases has not yet been sufficiently investigated, some studies have shown that polyphenolic compounds have some impact on fungi growth. In order to contribute with new knowledge, this research deals with monitoring the growth of P. expansum on apples, patulin detection by LC/MS-MS, determination of polyphenol profile by validated HPLC method, and determining the effect of polyphenolic compounds on fungi growth and patulin production during apple storage. The results of this study have shown that Croatian traditional apple cultivars harvested from family farm Horvatić contain higher concentration of polyphenolic compounds and higher antioxidant activity. At the same time, they showed more resistance to infection by P. expansum than conventional ones. The higher content of dihydrochalcones and flavanols encouraged the biosynthesis of patulin in examined cultivars. However, the higher content of non-flavonoids such as 2-6 dimethoxybenzoic acid, 4-hydroxycinnamic acid and chlorogenic acid leads to decrease in content of patulin. In conclusion, it seems that content of polyphenols and patulin production are correlated.

Interactions of polyphenols from traditional apple varieties 'Bobovac', 'Ljepocvjetka' and 'Crvenka' with β-Glucan during in vitro simulated digestion

Interactions between β-glucan and polyphenols might have an effect on polyphenol digestion and bioaccessibility. The influence of β-glucan on in vitro gastrointestinal digestion of polyphenols of traditional apple varieties was studied. Polyphenols were chemically and enzymatically extracted, and identified and quantified with high-performance liquid chromatography. Simulated digestion of peel and flesh of apples was conducted. Polyphenols released in digestion in lower amounts than occur naturally in apples. Their content increased from the oral to the gastric, then decreased in the intestinal phase (up to 21% (peel) and 16% (flesh) were recovered) where anthocyanins and flavan-3-ols were not found. β-glucan decreased (oral and intestinal digestion of peel) or increased (gastric digestion of peel; oral, gastric, intestinal digestion of flesh) the recovered polyphenols. Interactions between β-glucan, polyphenols and enzymes might have influenced these effects. β-glucan is suggested to increase the polyphenol content reaching lower parts of the digestive tract.

Impact of condensed tannin interactions with grain proteins and non-starch polysaccharides on batter system properties

Proanthocyanidins (PA) cross-link wheat gluten proteins and dramatically enhance batter viscosity; PA could similarly affect related grains. This study aimed to determine PA effect on viscosity and pasting properties of barley, rye, and oat flours, and the relative contributions of PA interactions with proteins and non-starch polysaccharides (NSP). PA significantly increased batter viscosity, stability, and RVA peak viscosity in rye and barley flours (2.8× and 1.2×, respectively). Interestingly, viscosity peaked distinctively ~75 °C in PA-treated rye and barley flours, and their isolated protein-starch systems, indicating prolamins unravelled and complexed with PA during heating. Oat was largely unaffected by PA, likely because of its protein composition. Furthermore, water-soluble rye NSP and arabinoxylans, but not barley β-glucans, significantly increased starch pasting viscosity with PA; oxidative gelation was not a factor. Thus, rye flour viscosity dramatically increased through interactive effects of PA on rye proteins and NSP, which could expand its food applications.