Modification of apple, beet and kiwifruit cell walls by boiling in acid conditions: Common and specific responses

Structural characterization of strawberry pomace

Strawberries are a nutrient dense food rich in vitamins, minerals, non-nutrient antioxidant phenolics, and fibers. Strawberry fiber bioactive structures are not well characterized and limited information is available about the interaction between strawberry fiber and phenolics. Therefore, we analyzed commercial strawberry pomace in order to provide a detailed carbohydrate structural characterization, and to associate structures with functions. The pomace fraction, which remained after strawberry commercial juice extraction, contained mostly insoluble (49.1 % vs. 5.6 % soluble dietary fiber) dietary fiber, with pectin, xyloglucan, xylan, β-glucan and glucomannan polysaccharides; glucose, fructose, xylose, arabinose, galactose, fucose and galacturonic acid free carbohydrates; protein (15.6 %), fat (8.34 %), and pelargonidin 3-glucoside (562 μg/g). Oligosaccharides from fucogalacto-xyloglucan, methyl-esterified rhamnogalacturonan I with branched arabinogalacto-side chains, rhamnogalacturonan II, homogalacturonan and β-glucan were detected by MALDI-TOF MS, NMR and glycosyl-linkage analysis. Previous reports suggest that these oligosaccharide and polysaccharide structures have prebiotic, bacterial pathogen anti-adhesion, and cholesterol-lowering activity, while anthocyanins are well-known antioxidants. A strawberry pomace microwave acid-extracted (10 min, 80 °C) fraction had high molar mass (2376 kDa) and viscosity (3.75 dL/g), with an extended rod shape. A random coil shape, that was reported previously to bind to phenolic compounds, was observed for other strawberry microwave-extracted fractions. These strawberry fiber structural details suggest that they can thicken foods, while the polysaccharide and polyphenol interaction indicates great potential as a multiple-function bioactive food ingredient important for gut and metabolic health.

Thermally Induced Covalent Cross-Linking of Proanthocyanidins and Pectin in Processed Fruit-Based Foods

The covalent interactions between proanthocyanidins (PAs) and pectin during thermal processing was investigated. An acid-butanol assay clearly showed that PAs were covalently bound to pectin. Computational studies indicated that a nucleophilic substitution reaction occurred between the carbocation generated by the PAs and carboxyl or hydroxyl groups on the pectin, leading to the formation of PAs-pectin adducts. Thermal processing and PAs significantly affected the physicochemical, functional, and biological properties of pectin. Thermal processing reduced the molecular weight and increased the gelling properties of pectin, whereas PAs increased both the molecular weight and the gelling properties. Finally, we found that the covalent attachment of PAs to pectin greatly enhanced its antioxidant, prebiotic, and α-glucosidase inhibitory activity. Overall, our results suggest that the thermal processing of fruits has the potential to induce a covalent interaction between PAs and pectin, which would impact the physicochemical characteristics and functional properties of pectin.

Effects of inoculation with a binary mixture of Lactobacillus plantarum and Leuconostoc citreum on cell wall components of Chinese Dongbei suancai

This study aimed to investigate the effects of inoculation with a starter culture consisting of Lactobacillus plantarum LNJ002 and Leuconostoc citreum BNCC 194779 on microbial community, cell wall polysaccharide characteristics, cell wall degrading enzymes, and microstructure during Chinese Dongbei suancai fermentation. The results showed that Lactobacillus (98.75%) was the dominant genus during fermentation of Dongbei suancai. The principal coordinates analysis (PCoA) suggested that inoculation with Lactobacillus promoted the stability of microbial community structure during Chinese Dongbei suancai fermentation. Besides, the lower content in cellulose (80.28 ± 2.61 ug/mg) and pectin (53.56 ± 2.67 ug/mg) observed in the inoculated fermented suancai. Simultaneously, the inoculated fermented suancai had the most decreases in SR 1 (70.35%) and SR 3 (72.06%) and the most increase in SR 2 (950%), which suggested that inoculation intensified the decrease of the linearity and the RG-1 branching degree of pectin. The contents of polygalacturonase (PG) and pectin methylesterase (PME) in inoculated fermented suancai were 21.06% and 21.86% higher than those in naturally fermented suancai. In addition, the surface of suancai leaves gradually changed from smooth to rough during fermentation, which was accelerated by inoculation. Moreover, Lactobacillus, Aspergillus, Wallemia and Mucor were all negatively correlated with cellulose and GalA. These results revealed that inoculation promoted the formation of dominant genus structure during suancai fermentation, changed the effects of enzymes on the degradation of cell wall components, thereby accelerated the formation of Chinese Dongbei suancai texture.

Extraction of polyphenols associated with pectin from olive waste (alperujo) with choline chloride

The main by-product from olive oil extraction (alperujo) was extracted with hot water, citric acid, natural deep eutectic solvent (choline chloride: citric acid), and only choline chloride. The purified extracts were composed of macromolecular complexes constituting polyphenols associated with pectin. The extracts were structurally characterized by FT-IR and solid-NMR spectroscopy and an in vitro test revealed distinct antioxidant and antiproliferative activity, depending on the extracting agents. The choline chloride-extracted complex contained the highest amount of polyphenols among the examined agents, which exhibited a strong antioxidant activity and significant antiproliferative capacity. However, the complex extracted by hot water showed the highest antiproliferative capacity in vitro against the colon carcinoma Caco-2 cell line. In this finding, choline chloride could be used as a novel, green and promising alternative to the conventional extracting agent for the production of complexes that combine the antioxidant activity of phenolic compounds and the physiological effects of pectic polysaccharides.

Acetic Acid Immersion Alleviates the Softening of Cooked Sagittaria sagittifolia L. Slices by Affecting Cell Wall Polysaccharides

This study investigated the mechanism for acetic acid pretreatment to improve cell wall integrity and thereby enhance the hardness of cooked Sagittaria sagittifolia L. slices by affecting polysaccharides in the cell wall. Distilled water immersion and 0.6% acetic acid immersion (the solid/liquid ratio is 1:10) for 15 h at room temperature could result in the conversion of pectin through different reactions during thermal processing. Combined in situ and in vitro analysis demonstrated that acetic acid pretreatment could promote the interaction of cellulose microfiber or hemicellulose with RG-Ⅰ side chains during thermal processing of S. sagittifolia L. slices, promote the entanglement between linear pectin molecules and make hemicellulose show a lower molecular weight under cooking, making it easy to firmly bind to pectin, which resulted in texture changes. The findings may help improve the texture of thermally processed vegetables and fruits and deep processing of starchy vegetables.

Enhancing anthocyanin-phenolic copigmentation through epicarp layer treatment and edible coatings to retain anthocyanins in thermally processed whole blueberries

Anthocyanins in processed fruit degrade significantly due to their heat and oxygen sensitivity and water solubility. Copigmentation for stabilizing anthocyanins is less effective for whole fruit due to anthocyanins' location within cell vacuoles surrounded by the epicarp layer as barrier to prevent copigment complexing with anthocyanins. This study investigated strategies for enhancing anthocyanin-phenolic copigmentation on blueberry surface, and integrated copigmentation with layer-by-layer (LBL) coating to retain anthocyanin stability in thermally processed blueberries. Results indicated that epicarp layer treatment of fruit by Tween 80 (T80) and CaCl₂ is important for enhancing anthocyanin-phenolic copigmentation. The sequential copigmentation treatment using T80, ferulic acid, and CaCl₂ (T80→FA→CaCl₂ ) or T80, tannic acid, and CaCl₂ (T80→TA→CaCl₂ ) resulted in higher (p < 0.05) retention of total monomeric anthocyanin (3.18 mg/g and 3.38 mg/g, respectively) in thermally processed blueberries after 7-day ambient storage than that of untreated fruit (2.79 mg/g). Percent polymeric color (PPC) of blueberries treated by T80→FA→CaCl₂ (15.5%) or T80→TA→CaCl₂ (17.4%) was lower (p < 0.05) than that treated by TA alone (22.5%). The LBL coating enhanced microstructure stability for preserving anthocyanins in thermally processed blueberries. This study demonstrated the effectiveness of sequential copigmentation of blueberries after epicarp layer treatment followed by LBL coating for enhancing anthocyanin stability in processed whole fruit. PRACTICAL APPLICATION: When anthocyanin-rich fruit is thermally processed, anthocyanins degrade and leach to aqueous packing solution because of its heat sensitivity and water solubility. This study developed an innovative technology through implementing sequential treatments of copigmentation and water- and heat-resistant coating for preventing heat and water degradation of anthocyanins in whole fruit during processing in aqueous media. The developed technology can be practically applied to enhance the quality and health benefits of thermally processed anthocyanin-rich whole fruit. The technology can not only be utilized to improve existing fruit products, but also develop new and novel fruit products.