Isolation, identification and evaluation of Lactic acid synthesis of bacteria in traditional fermented products in Vietnam

Abstract

Nowadays, many food products are promoted as being particularly healthy due to the characteristics of certain strains of lactic acid bacteria. Lactic acid bacteria (LAB) play a vital role in different fields, including food, pharmacy due to their benefit for young children, pregnant women and the elderly. LAB is one of the most significant groups of microorganisms used in food fermentations. They improve the flavour and texture of fermented foods. Moreover, LAB kills food spoilage bacteria by developing growth-inhibiting compounds. In this study, seven strains of LAB were isolated from traditional fermented products in VietNamm including fermented rice, kimchi, and yoghurt. Moreover, LAB isolated was identified by amplification and sequencing of 16s rDNA gene. The isolated strains were Lactobacillus plantarum (M2 and M7), Lactobacillus paracasei (M4), Lactobacillus sakei (M10), Leuconostoc mesenteroides (M15), Lactobacillus curvatus (M17), Lactobacillus delbruekii sub sp. (M19). Cultural characteristics of M1 and M7 surface colony are 2mm wide, raised, smooth and white on MRS agar. The morphology of the colonies M4 and M10 is rounded, smooth, light yellow. Nevertheless, M4 and M10 are quite different in colour, white and light yellow, respectively. Moreover, M15 colonies are convex, with flat edges, smooth, semitransparent. M17 and M19 are small, normally rough and non-pigment. Acid lactic content produced by the isolated strains determined by spectral absorbance at 390 nm with FeCl₃ (0.2%), was highest in M2 strain (37.814g/l), followed by M17 (32.357g/l), M19 (27.336g/l), M4 (20.853g/l), M10 (9.408g/l), M7 (8.864g/l), and M15 (6.645g/l). In this study, the highest lactic acid content produced was M2 stain (Lactobacillus plantarum) and the lowest was M15 (Leuconostoc mesenteroides).