The bioaccessibility, bioavailability, bioactivity, and prebiotic effects of phenolic compounds from raw and solid-fermented mulberry leaves during in vitro digestion and colonic fermentation

The bioaccessibility and bioactivity of phenolic compounds in mulberry leaves (MLs) relate to the digestion process. This study was aimed at investigating the release of phenolic compounds, as well as the potential bioactivities of raw MLs (UF-MLs) and solid-fermented MLs (F-MLs) during in vitro digestion and colonic fermentation. Antioxidant activities and phenolic compounds released in the digested extracts are shown in decreasing order of location: intestinal > oral > gastric. The bioavailability of total phenolics and flavonoids in F-MLs were 10.14 ± 1.81 % and 6.66 ± 0.55 %, respectively. There was no significant difference in the inhibitory activity of α-glucosidase during gastrointestinal digestion. For colonic fermentation, the highest free radical-scavenging ability of DPPH and ABTS was found at 24 h and 48 h, respectively. The release of phenolic compounds was not significantly different after 48 h of colonic fermentation. LC-MS/MS showed that liquiritigenin, apigenin, chlorogenic acid, and ferulic acid were the major compounds released in the small intestine digestion, and valerenic acid was the primary colonic metabolite. 16S rDNA showed that UF-MLs promoted the growth of Bifidobacterium and F-MLs lowered the Firmicutes-to-Bacteroidetes ratio. Furthermore, F-MLs increased the concentration of acetic acids (25.75 ± 0.86 mM) after 24 h of colonic fermentation. The results of this study indicated that F-MLs exhibit relatively higher phenolic bioaccessibility, antioxidant activities, and SCFA production and are a promising candidate as a health food supplement.