Xanthan gum modified fish gelatin and binary culture modulates the metabolism of probiotics in fermented milk mainly via amino acid metabolism pathways

1H NMR combined with multivariate data analysis were applied to investigate the effects of fish gelatin (FG) addition and co-culture of Lactobacillus acidophilus LA-5 (La-5) and Bifidobacterium lactis BB-12 (Bb-12) on the growth and metabolic pathways of the probiotics themselves. The results showed that the addition of FG had no significant effects on the growth of probiotics, but co-culture did promote the growth of probiotics, especially for Bb-12 (up to 2 log CFU/mL). FG addition inhibited amino acids synthesis and TCA cycling in Lacticaseibacillus paracasei subsp. paracasei CASEI 431 (L431) to some extent. However, for the single La-5 strain, these pathways were promoted. As for mixed bacterial cultures, Bb-12 promoted amino acids metabolism, sugar transport and energy metabolism in La-5. These findings suggested that the metabolic profile of probiotic bacteria can be adequately explained by metabolic pathway analysis, which also provides theoretical guidance for the industrialization of functional fermented milk.