Release and transformation patterns of polyphenols of rice at different milling degrees during in vitro gastrointestinal digestion and colonic fermentation

• Release and transformation of polyphenols of rice at different DOMs were investigated in vitro. • Colonic fermentation significantly promoted polyphenols release in milled rice. • Hydrocinnamic acid and benzoic acid significantly increased after colonic fermentation of rice at DOM 3.50%. • Phascolarctobacteria and Enterococcus dominated the release and transformation of polyphenols. • Rice at DOM 3.50% could be developed as a whole-grain product balancing nutrition and texture. Milling is a key step in rice processing, while it also affects the content and bioavailability of nutrients. In the present study, the release and transformation of polyphenols and their potential activities of rice at different degrees of milling (DOMs) were investigated via in vitro gastrointestinal digestion and colonic fermentation models. Results showed that polyphenols were stable in the gastrointestinal tract and were released continuously during colonic fermentation, and peaked after a 48-h fermentation. LC-MS analysis revealed that the dominant polyphenols in rice at DOM 3.50% were hydrocinnamic acid and benzoic acid after colonic fermentation. 16S rRNA analysis revealed that rice at different DOMs significantly changed the microbial composition, and gut microbiota effectively released more bound polyphenols by utilizing dietary fiber. Among them, Phascolarctobacteria and Enterococcus as the distinguished bacteria in rice at DOM 0% and 3.50% were related to the release and biotransformation process of polyphenols. Texture profile analysis further suggested that the hardness and stickiness were improved in moderately-milled rice (DOM 3.50%) than those in brown rice. Collectively, this study suggested that moderately-milled rice could be developed as rice products balancing nutrition and texture.