Changes in physicochemical characteristics and metabolites in the fermentation of goji juice by Lactiplantibacillus plantarum

Untargeted and targeted metabolomics based on LC-MS/MS was applied here to investigate the changes in metabolites following Lactiplantibacillus plantarum (L. plantarum) fermentation of goji juice. The changes in physicochemical characteristics, free amino acid and organic acid levels were quantified. Total phenols, total flavonoids, and antioxidant activity were increased after these L. plantarum fermentation. 31 primary metabolites were screened out by comparison between two groups using multivariate statistical analysis. L. plantarum consumed reducing sugar and most varieties of amino acids. Gamma amino butyric acid (GABA) and phenylacetaldehyde were significantly accumulated via precursor of glutamate and phenylalanine, respectively. Indole-3-lactic acid (ILA) was the characteristic secondary metabolite after fermentation. There were 6.25 and 4.19 mg/L ILA accumulated after LP-D and LP-F fermentation, respectively, whereas it was not detected in goji juice. The accumulation of tyrosol was strain-dependent. Part of the bitter-taste amino acids, including l-methinoine, l-phenylalanine and tryptophan, were converted into their corresponding acetyl-derivatives, which represented umami or kokumi taste. Overall, fermentation by L. plantarum strains altered the metabolite profile and increased the levels of several biologically active substances of goji juice. These results deepen the understanding of L. plantarum metabolism, and the bioconversion associated with flavor and bioactive compounds unraveled here can be used as references in other plant-based materials for LAB fermentation.