Cooperation mechanism of flavonoid transformation by Bifidobacterium animalis subsp. lactis and Lacticaseibacillus paracasei.

Elaeagnus moorcroftii Wall. ex Schlecht (EWS) as a suitable food matrix contains abundant flavonoids for promoting human health, this study aimed to use flavonoid-targeted metabolomics and transcriptome sequencing to investigate the transformation of flavonoids in EWS juice (EWSJ) by mono- and mixed-cultures fermentations of Bifidobacterium animalis subsp. lactis HN-3 (B.an3) and Lacticaseibacillus paracasei YL-29 (L.cp29). A total of 33 flavonoids were identified in mono- and mixed-cultures fermented EWSJ. Among them, fermentation by B.an3 produced specific deglycosylation products (kaempferol (17.6 mmol/L) and luteolin (4.5 mmol/L)) and methoxylation products (syringaldehyde (59.05 mmol/L)), and fermentation by L.cp29 resulted in a specific deglycosylation product (quercetin (9.2 mmol/L)). The co-culture fermentation further increased the levels of isorhamnetin (52.3 mmol/L), and produced a specific product (homoplantaginin (0.03 mmol/L)), which significantly increased the bioactive-form flavonoids. Moreover, we analyzed changes in different flavonoid metabolites and differential genes before and after fermentation. After L.cp29 fermentation the expression of glycoside hydrolases and oxidoreductases were increased compared to other groups. After B.an3 fermentation the expression of isomerases and synthetases were increased compared to other groups. In particular, 6-phosphogluconolactonase (Pgl) and glucose-6-phosphate isomerase (Pgi) were increased in B.an3 fermentation. Thus, we validated the predicted transformation reactions by the biotransformation of flavonoids by the collected strains and crude enzyme extracts of B.an3 and L.cp29. These findings provided a basis for the development of functional plant-based foods with enhanced bioactive flavonoids.