Variations of probiotic characteristics among Nisin producing L. lactis strains derived from milk and fermented grain

Abstract

The aim of the study was to select nisin producing Lactococcus lactis strains isolated from milk and fermented grain with probiotic characteristics and suitable for industrial application. In total 12 nisin producing Lactococcus lactis strains isolated from raw cow, goat milk and fermented grain samples were evaluated for their probiotic potential. Properties such as bile tolerance, tolerance to low pH, antagonistic activity, demonstration of safety have been evaluated. Although acidity is reported to have the most negative effect on survival of probiotics, all tested strains were able to tolerate acid with a survival rate being over 84% after 3 h incubation with PBS (pH 2.5) solution. Two strains showed 98% survival rate after 3h incubation with the number of viable bacteria count being 7.8±0.13 and 7.5±0.01 log CFU/ml respectively. Not all strains were resistant to 0.3% ox bile after 24 h incubation. Only seven strains showed resistance whereas one strain showed 74% survival rate after 24 h incubation with the number of viable bacteria count being 5.6±0.03 log CFU/ml. All strains were evaluated for hemolytic activity on sheep blood agar. α-hemolytic activity was determined for three strains, none of the strains showed β-hemolytic activity and φ-hemolytic activity as determined for nine strains. Antibacterial activity against eight pathogenic and food spoilage bacteria including Bacillus cereus, Salmonella typhimurium and others were also assessed. All tested strains showed clear inhibition against tested bacteria. Against Salmonella typhimurium and Eschericia coli a better antagonistic activity was expressed by isolates from fermented grain samples and against Listeria monocytogenes a better antagonistic activity was expressed by isolates from raw milk samples. Six strains had properties that are characteristic for probiotics with potential for application in functional foods (1 isolated from raw cow milk and 5 from fermented grain samples). These st