Strain-specific metabolic variations in polyphenols and saccharides during lychee fermentation

Lychee is recognized for its nutritional value and abundance of polyphenolic compounds, which contribute to various potential health benefits. However, its high sugar content restricts its suitability for certain consumer groups. Hence, lychee pulp was subjected to fermentation with seven lactic acid bacterial (LAB) strains, and the differential metabolic patterns of polyphenols among these strains were systematically investigated using UPLC-Q-Exactive-Orbitrap-MS/MS. Notably, two previously unreported metabolites—dihydroxybenzaldehyde-rhamnoside and anisaldehyde—were discovered. The former originates from the metabolic conversion of quercetin-3-O-rutinoside-7-O-α-L-rhamnoside, the characteristic flavonoid in lychee pulp, while the latter derives from ferulic acid metabolism. Meanwhile, LAB fermentation resulted in nearly complete degradation of glucose, fructose, and sucrose, with a sugar reduction rate exceeding 90 %, alongside significant production of short-chain fatty acids. Among the strains, Limosilactobacillus fermentum exhibited the highest yield. The present study provides a theoretical basis for screening functional LAB strains and developing low-sugar, high-polyphenol functional lychee products.