In vitro fermentation of kodo and kutki millets by human gut microbiota: Gut microbiota and metabolomic analysis

Millets are underutilised cereals packed with several bioactive components. The effect of Kodo millet (KOM) and Kutki millet (KUM) on the modulation of gut microbiota and metabolites produced during batch in vitro fermentation using human faecal samples was investigated. A two-fold increase in Firmicutes and an 18.95- and 9.74-fold increase in the relative abundance of Actinobacteria were observed in the KOM and KUM groups respectively. Furthermore, Bacteroidetes counts decreased by 17.4% in the KOM group and by 98.2% in the KUM group. Metabolomic analysis revealed different abundances of metabolites in different millet groups. The concentration of acetate, lactate and propionate increased significantly in the KOM group, while only a significant increase in lactate was recorded in the KOM group. Odd chain fatty acids (OCFAs) were abundant in both groups. The KUM group was enriched in tridecanoic acid, and pentadecanoic acid, while KOM had a higher concentration of dodecanoic acid and cis-10-heptadecenoic acid. Correlation analysis of gut microbiota and metabolome revealed the association of beneficial metabolites with Caproiciproducens, Lactobacillus, Veillonella, Blautia, Faecalibacterium and Prevotella. Furthermore, PICRust analysis confirmed the upregulation of various metabolic pathways including glycan biosynthesis and metabolism, lipid, carbohydrate and amino acids metabolism, etc in millet groups. Collectively, the study contributes to the understanding of the millets-human gut microbiota interaction and suggests that different millets can be used for the formulation of specialized food that targets specific gut microbiota.