RESUMO
Sourdough starter contains lactic acid bacteria which can improve quality and taste of bread. The lactic acid bacteria in sourdough have antifungal and antibacterial activities. As some lactobacilus-fermented traditional foods contain salt as a preservative, this study was initiated to investigate the effect of different concentrations of sodium chloride on the kinetics of growth and antimicrobial potential of autochthonous isolates of lactobacilli isolated from Iranian traditional sourdough. MRS broth media containing sodium chloride concentrations up to 7% were inoculated with two sourdough isolates of lactobacilli, namely, Lactobacillus casei and Lactobacillus fermentum. The kinetics of growth of individual lactic acid bacteria at different concentrations of sodium chloride was investigated using the conventional plate-count method. Also the antibacterial effects of supernatants of the lacto bacterial strains grown in media with different salt concentrations on several pathogenic bacteria were assessed. The pathogenic strains included methicillin-resistant Staphylococcus aureus, Kelebciella pneumonia, and Pseudomonas aeruginosa. The highest growth of both lactobacilli isolates was 10[9] cfu/ml, which occurred at a salt concentration of 2-4%; at a concentrtation of 5% salt the total bacterial counts dropped to 7.5x10[8]. There were further decreases in the lactic acid bacterial counts at a 7% salt concentration to 3.7x10[6] and 2.5x10[5] for L. casei and L. fermentum, respectively. Both lactobacilli isolates tolerated salt concentrations up to 5%, but L. casei was found to be more salt-tolerant than L. fermentum. Salt concentrations did not affect the antimicrobial effects of supernatants of individual lactobacilli isolates. However, low bacterial biomass achieved at high salt concentrations negatively affected antipathogenic effect of these isolates, presumably due to less metabolite production