Phenolic, Flavonoid, Short-Chain Fatty Acid, and Probiotic Biomass Changes During In Vitro Digestion and Fermentation...

Litchi processing generates large quantities of seed by-products that are rich in starch and polyphenols but remain underutilized. In this study, the bioactivity and prebiotic potential of litchi seed vinegar (EHA-B-S1), a sustainable product derived from litchi seed by-products, were systematically evaluated. EHA-B-S1 displayed measurable in vitro antioxidant activity: total antioxidant capacity (4 mmol Trolox equivalents per mL), DPPH radical-scavenging of 50 µmol Vc equivalents per mL, and ABTS radical-scavenging activity of 1.0 mmol Vc equivalents per mL. EHA-B-S1 displayed moderate inhibitory capacity against α-amylase, α-glucosidase, and pancrelipase, and its performance was close to that of acarbose and orlistat. During probiotic-mediated fermentation, EHA-B-S1 rapidly acidified the fermentation environment, treatment resulted in higher measured biomass of Lactobacillus acidophilus, Lactobacillus rhamnosus, Lactiplantibacillus plantarum, and partially sustained Bifidobacterium longum compared with the control. The increase in metabolic activity showed higher short-chain fatty acid production, especially acetic acid, and expanded flavonoid diversity from 36 to 47 detected compounds; total flavonoid content increased to approximately 176% of the initial level. Network pharmacology analysis further predicted that these flavonoids may be associated with multiple metabolic and inflammatory pathways, providing hypotheses for future mechanistic studies. Collectively, the experimentally observed in vitro activities and fermentation-associated metabolite changes support further investigation of litchi seed vinegar as an upcycled bioactive fermented-food candidate, whereas its molecular targets, physiological effects, and health relevance require targeted cellular and in vivo validation.