Microbial biotransformation of polyphenols during in vitro colonic fermentation of masticated mango and banana.

Mango and banana cell structures, which survived in vivo mastication and in vitro gastrointestinal digestion, were fermented in vitro for 48h. For both fruits, flavonoids and phenolic acids were liberated and underwent microbial metabolism involving ring fission, dehydroxylation and decarboxylation. UHPLC-PDA/Q-ToF-MS profiles revealed rapid degradation (72-78%) of most intact precursors (epicatechin and several unidentified compounds) within 10h, before the exponential phase of the cumulative gas production. Concomitant formation of catabolites (e.g. 4-hydroxyphenylacetic acid) occurred within 4-8h, while metabolism of catechin derivative and 3-(4-hydroxyphenyl)propanoic acid continued slowly for at least 48h, suggesting intact plant cell walls can be a controlling factor in microbial susceptibility. Untargeted PCA and OPLS-DA demonstrated clear classifications in the compositional fruit type and compound profiles as a function of time. Clusters and distinct discriminating compounds were recognised, which could lead to subsequent biomarker identification for establishing differences in polyphenol microbial metabolism of various fruit matrices.