Simulated gastrointestinal digestion and in vitro colonic fermentation of carob polyphenols: Bioaccessibility and bioactivity

Carob is a well-known tree for its nutritional and health-promoting edible pods due to its high phenolic contents. It was aimed to investigate: 1) carob phenolic profiles; soluble free, soluble conjugated and bound, 2) bioaccesibility of those phenolics during simulated gastrointestinal digestions, plus in vitro fecal fermentations, 3) their antioxidant properties, also 4) α-amylase and α-glucosidase inhibitory activities. Ten phenolic acids and six flavonoids were detected in soluble (free and conjugated) and insoluble fractions of undigested carob. After in vitro gastrointestinal digestions, the most bioaccessible phenolic acids and flavonoids were gallic acid (647.4%), chlorogenic acid (485.4%), (+)-catechin (558.3%) and rutin (267.2%). Myricetin (79.5%) and gallic acid (20.0%) were the most abundant metabolites of residual fraction of carob phenolics after fecal fermentations. Antioxidant capacity of digested carob has increased significantly (p < 0.05); DPPH (107 mg GAE/g), ABTS (399 mg TE/g) and ORAC (415 μmol TE/g). Both undigested carob and its digested fractions showed a positive dose-dependent inhibition of α-amylase activity (0.3–1.0 mg/mL). The findings from this study showed first time report on carob phenolic profiles (soluble and insoluble) and their bioaccessibility during digestions and fecal fermentations. Carob phenolic might influence glucose metabolism by inhibiting carbohydrate digestion