New insights into the changes of structure-activity characteristics from dark beer melanoidins through different chemical treatments and in vitro digestion and fermentation

Dark beer melanoidin (BM) exhibited colloidal properties and negative charge. • Glycosidic, peptide and non-covalent bonds were broken after chemical treatment. • Structure and bioactivity of BM were relatively stable during in vitro digestion. • The levels of polyphenolics and SCFAs were increased during colonic fermentation. • Phloroglucinol was the main phenolic compound during colonic fermentation. Melanoidins are brown macromolecular products of Maillard reaction formed through thermal processing, which provide unique flavor and bioactive function of food. This study aims to reveal the changes of structure and bioactive characteristics in beer melanoidin-rich fraction (BM) during different chemical treatments and in vitro digestion and fermentation. The results showed that BM had colloidal properties with 24.21–99.28 nm and negative charge, which mainly contained carbohydrates. In addition, microscopic morphology showed surface cracks after acid treatment, blocky particles after alkali treatment, and some porous small particles after salt treatment. These might be caused by the disruption of polysaccharide, protein, and the skeleton structure through spectra. Moreover, during simulated in vitro digestion stage, Mw of BM was slightly decreased, which might be due to the breakage of glycosidic bonds. Microscopic morphology presented a relatively complete block structure. However, the contents of total phenolics and flavonoids and the production of short-chain fatty acids were significantly increased during colonic fermentation process. Phloroglucinol was the main phenolic compound and its content also increased during colonic fermentation. Collectively, the results indicated that BM had relative stability during the digestion stage, and released bioactive compounds during colonic fermentation. These findings suggest that BM, as a novel colloidal prebiotic, possesses potential role in intestinal health. Download: Download high-res image (164KB) Download: Download full-size image