Purpose: The aims of this study were to isolate the EPS-producing lactic acid bacteria (LABs) from kefir, (ii) purify their EPS, (iii) and identify its antimicrobial activity against two major foodborne pathogens.
Methods: A total of 22 strains of LAB were isolated from kefir and the ability of each strain to produce EPS was determined by the ethanol and trichloroacetic acid precipitation method. In addition, the antimicrobial activities of the EPS produced by Lactobacillus kefiranofaciens DN1 (EPS_DN1) against Listeria monocytogenes and Salmonella Enteritidis were assessed by growth curve analysis. Finally, the monosaccharide composition of EPS_DN1 was determined by High-Performance Size-Exclusion Chromatography (HPSEC).
Results: A total of 22 strains, including eight strains of L. kefiranofaciens, two strains of Lactobacillus kefiri, seven strains of Lactococcus lactis, and five strains of Leuconostoc mesenteroides, were isolated from kefir. The ability of each strain to produce EPS was determined and L. kefiranofaciensDN1 was found to have the highest EPS yield among all isolates (2.20 g/L). Moreover, EPS_DN1 at a concentration of at least 1% was able to exert bactericidal effects against both pathogens. Interestingly, results of HPSEC analysis indicated that EPS_DN1 was not the major EPS of kefir called kefiran, suggesting that EPS_DN1 represents a novel bioactive compound.
Significance: EPS_DN1 is a novel polysaccharide produced by L. kefiranofaciens isolated from kefir, and could be applied to develop natural antibiotic alternatives.