Effects of Sequential Fermentation with Saccharomyces bayanus and Lactobacillus brevis on the Metabolite Composition and Antioxidant Activity of Chinese Yam Juice

Chinese yam (Dioscorea opposita Thunb.) is a nutrient-rich tuber with recognized health benefits, yet its application in beverage products remains limited due to processing and formulation challenges. In this study, a sequential fermentation strategy was adopted, using Saccharomyces bayanus followed by Lactobacillus brevis to enhance microbial viability and metabolic activity in Chinese yam juice. Samples were collected as an unfermented control (CY), yeast-fermented juice (SP), and sequentially fermented juice (LB). Microbial analysis showed that sequential fermentation supported high LAB viability, reaching 8.92 log CFU/mL in LB, accompanied by a progressive decrease in pH from 5.67 (CY) to 4.27 (LB). Untargeted LC-MS/MS metabolomics identified 1442 metabolites and revealed distinct shifts in the metabolic composition of CY, SP, and LB, indicating stage-dependent modifications of metabolic pathways. Targeted analyses confirmed substantial depletion of sucrose and maltose during fermentation, while trehalose accumulated from undetectable levels in CY to 5.23 mg/g in SP and 7.49 mg/g in LB. Organic acid profiling demonstrated marked increases in lactic and succinic acids, consistent with microbial carbohydrate metabolism. Total phenolic and flavonoid contents increased by 58% and 30%, respectively, while antioxidant capacity (DPPH, ABTS, and FRAP) improved by up to 120% after sequential fermentation. The final fermented beverage (LB) contained a low ethanol concentration of 0.8% (v/v). Sensory evaluation indicated that sequential fermentation improved the overall flavor, aroma, and acceptability of the Chinese yam juice. These findings demonstrate that sequential fermentation with S. bayanus and L. brevis effectively enhances the bioactive composition and antioxidant potential of Chinese yam juice, supporting its development as a functional fermented beverage.