The fermentation of whey protein and mulberry polyphenols by forming protein-phenolic adducts: Improved digestions

The impacts of forming adduct between whey protein (WP) and mulberry polyphenol (MP) on the digestion and fermentation of WP and MP were investigated using an in vitro model. The results showed that MP increased the in vitro antioxidant capacity of WP digestive products. After forming adduct the total extractable phenolic content of MP dropped from 440.20 mg GAE/g to 21.53 mg GAE/g. The total extractable phenolic content of WP-MP group decreased from 21.53 mg GAE/g to 11.77 mg GAE/g after the oral digestion, then slightly increased to 12.43 after the gastric digestion and continuously increased to 20.43 mg GAE/g after the intestinal digestion. Extractable individual phenolic compounts exhibited the similar tendency, in which cyanidin-3-O-glucoside, cyanidin-3-O-rutinoside, p-coumaric acid, quercetin and kaempferol were still detectable while protocatechuic and neochlorogenic acid increased after intestinal digestion of WP-MP adduct. Incorporation of MP inhibited the oral and gastric digestion but enhanced the intestinal digestion of WP, and the degree of hydrolysis of WP increased 9.70% after intestinal digestion compared to the control. The fermentation of non-dialyzable residue of WP-MP by gut flora decreased the pH value from 7.18 to 4.82 and increased the proliferation of beneficial bacteria and the production of short-chain fatty acids. These findings indicated that WP-MP adduct increased the digestion of WP and the bioaccessibility of MP, could improve the intestinal health and could be used as a new healthy food ingredient.