Effect of Lactobacillus plantarum and Lactobacillus acidophilus fermentation on antioxidant activity and metabolomic profiles of loquat juice

Nonalcoholic fermentation could improve the organoleptic quality and functionality of fruit juice, and lactic acid bacteria (LAB)-fermented fruit juice has been proven to be beneficial to human health. However, LAB exhibit strain specificity with different food matrices. In the present study, the effects of L. plantarum and L. acidophilus on the physicochemical characteristics, antioxidant activity and metabolomics of loquat juices were investigated. Both LAB strains fermentation could significantly enhance the antioxidant activity of loquat juice. L. acidophilus grows faster than L. plantarum in loquat juice, but L. plantarum fermentation more effectively increased the total flavonoid content. Nontargeted metabolomics analysis based on UHPLC-Q Exactive HF-X/MS were performed to reveal the different metabolic profiles between LAB fermentation. A total of 776 metabolites were identified and annotated. The significant differentially regulated metabolites were concentrated mainly in lipids and lipid-like molecules; organic acids and derivatives; amino acids, peptides, and analogs; phenolic compounds and terpe-noids. The regulation of metabolites plays a very important role in the flavor reconstruction and functional improvement of loquat juices. In addition, the metabolic profiles between L. plantarum-and L. acidophilus-fer-mented loquat juices were different, and the application of cofermentation of these two strains may be considered in future studies.