Characterization of lactic acid bacteria isolated from pickled vegetables as potential starters for yogurt preparation

Abstract

The process of preliminary isolation and selection of lactic acid bacteria from Vietnamese traditional fermented vegetables is done on the basis of (i) isolation and (ii) qualitative and quantitative analysis of lactic acid as the basis for the inspection and selection of lactic acid bacteria with strong antibacterial characteristics. The selected lactic acid bacteria were applied for yoghurt fermentation with different bacterial densities (104-108 CFU/ml). The changes in pH value during fermentation time and sensory quality of product were evaluated. The research results showed that 48 strains were isolated from Vietnamese traditional fermented vegetables. Among them, 35 isolates (33 rod-shaped and 2 spherical-shaped) met the criteria of lactic acid bacteria. There were 15 isolates that were able to produce the highest amount of lactic acid, in which the rod-shaped bacteria has higher lactic acid production than that of the spherical-shaped. Four strains (S 1.2, S 5.5, S 5.7, XK 1.4) of these 15 strains that were tested antimicrobial activity based on the agar spot test and agar well diffusion test, could produce bacteriocin against Bacillus subtilis. Based on the result of DNA sequencing method, strains XK 1.4 and S 1.2 with strong antibacterial production belonged to Lactobacillus plantarum (similarities 97% and 99%). The yoghurt that was prepared by inoculating 108 cfu/mL of starter cultures (strains XK 1.4 and S 1.2) had the pH value of 4.5 after incubating for 7 hrs, and achieved the good sensory quality.