Polyphenol-enriched yam bean via vacuum impregnation: enhanced antioxidant activity and metabolite bioconversion during in vitro colonic fermentation.

Yam bean (Pachyrhizus erosus L.) is an underutilized Mexican tuber valued for its dietary fiber but limited in polyphenols, reducing its functional potential. This study evaluated the effect of vacuum impregnation (VI) with mango seed polyphenolic extract on its in vitro colonic fermentation. Mango seed extract was obtained via ultrasound-assisted extraction and incorporated into yam bean slices through VI (150 mBar, 15 min), followed by dehydration and in vitro gastrointestinal digestion to isolate the indigestible fraction. Four treatments were tested: T1 (extract + vacuum), T2 (extract without vacuum), and two water controls (T3 and T4). Digested samples were fermented with pooled human fecal microbiota for 24 h under anaerobic conditions. T1 showed significantly higher total soluble phenols (6.30 ± 0.48 mg GAE/g at 3 h), antioxidant activity (5.94 ± 0.12 μmol TE/g at 6 h by DPPH), and pH reduction (4.59 ± 0.04 at 24 h), compared to T2 and controls. HPLC-DAD-MS identified 24 phenolic compounds and metabolites, with T1 showing greater abundance and earlier appearance of gallic acid, pentagalloyl glucose, ellagic acid, and urolithins A and C. GC-MS revealed that esters dominated early fermentation in T1, while fatty acids predominated after 12 h in all treatments. The higher metabolite diversity and concentration in T1 suggests a stronger interaction of polyphenols with the yam bean matrix via VI, enhancing microbial bioconversion. These results demonstrate that VI is a promising strategy for improving the functional properties of plant matrices using polyphenol-rich by-products, contributing to the development of functional foods aimed at intestinal health.