Phenolic bioaccessibility, antioxidant, and antidiabetic effects of indigenous fermented coffee beans after simulated gastrointestinal digestion and colonic fermentation

Abstract

Postharvest fermentation could bring significant changes in the chemical profile of coffee beans so that the nutritional aspects. This study comprehensively evaluated the effects of indigenous fermentation on coffee beans in green and roasted status by quantifying the phenolic compounds and estimating their bioaccessibility, crude absorbability, antioxidant, enzyme inhibitory activity, and SCFA production during in vitro digestion and colonic fermentation. Compared to the unfermented (UF) beans, in both phenolic extract and absorbable fraction during digestion, fermented (F) coffee beans in roasted status showed similar or lower phenolic content and antioxidant activities. Only light-roasted FK showed significantly higher TPC (50.9 mg GAE/g) and TFC (1.21 mg QE/g) than the UFK (35.8 mg GAE/g, 1.06 mg QE/g) in the gastric absorbable fraction. However, medium-roasted FK performed significantly outstanding α-amylase (9.67%) and α-glucosidase (21.86%) inhibition activities than that of UFK (7.41%, 18.31%). The bioaccessibility and crude absorption rate of total phenolics and chlorogenic acid were relatively higher during the in vitro digestion and colonic fermentation of fermented green coffee beans. The differences were eventually eliminated along with the intensification of roasting due to the thermal degradation. The total SCFAs produced from fermented beans was only up to 2.185 mM after 16 h fecal reaction, which is significantly lower than that of the unfermented (<3.216 mM) because of the hydrolyzation of polysaccharides during the postharvest fermentation. Therefore, in the long term, fermented coffee beans could perform higher nutritional values with higher phenolic absorption efficiency, especially chlorogenic acids, and antidiabetic potential.