16S metagenomics and metabolomics unveil the microbial compositions and metabolite profiles in Dahi, a traditional Indian fermented milk product prepared by the backslopping method

Fermentation of milk contributes to an array of organoleptic and nutritional changes, which is largely governed by the metabolic activity of starter cultures. Dahi, a popular traditional fermented milk product of India, varies considerably from its commercial counterparts due to diversity in household production practices and the use of undefined microbial consortia as inoculants. Herein, we investigated the unexplored bacterial signatures and metabolic profiles of traditional Dahi from northern region of India using 16S metagenomics and untargeted gas chromatography-mass spectrophotometry. We found Firmicutes followed by Proteobacteria as the dominant phyla, while Lactobacillus and Streptococcus were the most prevalent lactic acid bacterial genera many species of which also serves as thermophilic starters. Notably, differential abundance of environmental bacteria like Bacilli, Prevotella, Oscillospira, Ruminococcus, and Acinetobacter were also observed in different samples. The study also revealed a total of 62 metabolites belonging to amino acids, fatty acids, sugars, and others metabolic intermediates, which also varied among regions. This highlights different production practices as influenced by milk type, heating methods, container choices and inoculum types leading to distinct microbiota succession and associated metabolites. This study provides valuable insights into the complexities as well as health benefits of indigenous fermented milks particularly Dahi and paves the way for future exploration of novel probiotic strains.

Graphical abstract