Characterization of newly isolated lactic acid bacteria for potential application of dairy products technological and safety improvement

Abstract

The aim of the study was to characterize technological and safety features of newly isolated Lactococcus lactis bacteria that could be used for dairy products technological improvement. Three presumptive L. lactis isolates from 31 tested cow milk samples were confirmed as Lactococcus lactis by PCR analysis. Properties such as antimicrobial activity, ability to rapidly produce acid, salt tolerance, diacetyl production, caseinolytic activity, antibiotic resistance and enzymatic activity were evaluated. Strains showed good antimicrobial activity against food spoilage and pathogenic bacteria such as Listeria monocytogenes. Escherichia coli, Brochtix thermosphacta and others. All strains were able to produce diacetyl, showed good acidifying activity as were able to induce pH drop from 1.17 to 1.66 units after 24 h, were salt tolerant with ability to grow at 6.5% NaCl, one strain showed caseinolytic activity. None of the tested strains showed resistance to tested antibiotics such as chloramphenicol, clindamycin, streptomycin, gentamicin, tetracycline, erytromycin and ampicillin above the breakpoints provided by European Food Safety Authority (EFSA, 2012). From enzymatic point of view, strains should not produce harmful enzymes like β-glucosidase or β-glucuronidase and none of the tested strains were producers of these enzymes. Other enzymatic activities evaluation revealed that one strain had strong activities of esterase (C4), esterase lipase (C8), lipase (C14), acid phosphatase and phosphohydrolase, enzymes that are important for cheese production. Other isolated L. lactis strains had weak activities of these enzymes. No or weak activities were determined for alkaline phosphatase, valine arylamidase, trypsin, α-galactosidase, α-glucosidase. N-acetyl-β-glucosaminidase, α-mannosidase and α-fucosidase. All teted L. lactis strains were found to be safe regarding enzymatic activity, had interesting technological characteristics and after further testing[...]