The impact of different lactobacilli fermentations on secondary metabolites of red raspberry juice and their biotransformation pathways via metabolomics based on UHPLC-MS/MS.

Secondary metabolites are a group of invaluable phytochemicals in raspberries. Fermentation process leads to changes in the phytochemical composition of fruits. This study aimed to investigate the influence of Lacticaseibacillus paracasei subsp. paracasei FBKL1.0328 and Lactiplantibacillus plantarum subsp. plantarum FBKL1.0310 on the secondary metabolites of red raspberry juice (CR) and uncover their conversion pathways via metabolomics based on ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). A total of 695 secondary metabolites in the unfermented and fermented samples were identified. There were 90, 83 and 52 differential secondary metabolites identified in LCR (L. paracasei FBKL1.0328 fermented raspberry juice) vs. CR, LPR (L. plantarum FBKL1.0310 fermented raspberry juice) vs. CR, and LCR vs. LPR, respectively. Certain phenolic acids (e.g. 3-phenyllacitc acid), flavonoids (e.g. galangin-7-glucoside), alkaloids (e.g. indole-3-lactic acid), and terpenoids (e.g. glucosyl 7-methyl-3-methyleneoctane-1,2,6,7-tetraol) were selected as the crucial differential metabolites. These two lactobacilli utilized distinct metabolic pathways for processing secondary metabolites. L. paracasei FBKL1.0328 primarily transformed flavonoids through the "Flavone and flavonol biosynthesis" pathway. L. plantarum FBKL1.0310 mainly converted phenolic acids via the "Tyrosine metabolism" pathway and the "Aminobenzoate degradation" pathway. Interestingly, L. plantarum FBKL1.0310 outperformed L. paracasei FBKL1.0328 in upregulating certain valuable bioactive compounds such as indole-3-lactic acid and 3-phenyllacitc acid, underscoring its potential as a promising strain for developing health-beneficial fermented fruit juices. These findings provide insights to how different lactobacilli modify secondary metabolite composition in red raspberry juice and offer valuable information for the industrial application of lactobacilli in fruit processing.