Tannin-Rich Extracts and Potentially Prebiotic Polysaccharides via Saccharomyces Cerevisiae Fermentation of Pomegranate Peel as a Juice Production By-Product

Pomegranate peel, accounting for 35-50% of the fruit's weight, is an underutilized by-product rich in ellagitannins and pectin. Although pomegranate juice has already been subjected to fermentation, this study aimed to demonstrate for the first time, that a simple fermentation process of pomegranate peel using Saccharomyces cerevisiae can yield tannin-rich extracts and enhance the potential prebiotic properties of pomegranate polysaccharides. Peels of ‘Wonderful’ and ‘G1’ cultivars, significantly differing in peel thickness, were used for fermentation applying three processes at room temperature monitored at 48 and 72 h. HPLC-DAD analysis showed that yeast-driven fermentation increased total tannin (up to 70% in dry extracts) compared with spontaneous fermentation (40-43%). A potential enhancement of prebiotic activity was associated with the reduction in the molecular weight of native polysaccharides (from a maximum of 705 kDa down to 26 kDa), as evaluated by DLS and DOSY-1H-NMR. Polysaccharides after fermentation were more effectively utilized by Bifidobacterium breve and Lactobacillus plantarum than those from control samples, as demonstrated by in vitro assays. These findings highlight a promising strategy for the valorization of pomegranate peel through the production of functional ingredients highly enriched in tannins and containing potentially prebiotic polysaccharides.