In vitro characterization of five indigenous lactic acid bacteria for their potential probiotic-rich semi-solid milk production

Abstract

The main objective of the present study is to characterize five lactic acid bacteria (LAB) isolated from traditional natural fermented foods (viz. Chhurpi, Janr, Kinema, Whey, Gundruk, and Sinki) of Darjeeling hills, West Bengal, India, for their use as potential probiotic starter cultures in homemade fermented semi-solid milk recipes. The isolated strains were characterized morpho-biochemically, with whole-cell protein profiles and 16S rRNA gene sequence analysis. The strains were also tested for antibiosis, hemolysis, and antibiotic sensitivity. The in vitro probiotic traits were assessed for gastric acid tolerance, bile salt tolerance, cholesterol-lowering activity, cell wall hydrophobicity, and the efficiency of folate and niacin production. The fermented milk-producing efficiency of the strains was assessed by measuring exopolysaccharide production, β-galactosidase activity, fermented milk quality, and residual lactose content. The biochemical and 16S rRNA gene sequence analysis identified the strains as Lactobacillus sp. LAB-04 (GenBank Ac. No.: HQ141911), Lactobacillus sp. LAB-06 (GenBank AC. No.: MG066499), Pediococcus sp. LAB-11 (GenBank Ac. No.: HQ141913), Lactobacillus sp. LAB-39 (GenBank Ac. No.: MG066500), and Lactobacillus sp. LAB-40 (GenBank Ac. No.: HQ141915). The in vitro probiotic parameters revealed that all five strains exhibited significant tolerance to acidic gastric conditions and bile salts (ox-bile, 5% w/v), as well as cell wall hydrophobicity and cholesterol-binding ability. The strains produced higher levels of exopolysaccharides in lactose- and glucose-amended media and showed good β-galactosidase activity. The semi-solid milk produced by the strains had negligible lactose content. The experimental evidence showed that these five LAB strains could serve as potent probiotic starter cultures in homemade fermented semi-solid milk recipes, and that the preparation could be beneficial for malnourished and lactose-intolerant individuals.