Genotypic and phenotypic characterization of exopolysaccharide-producing lactobacillus strains isolated from kefir grains

GANGOITI V; HAMET M F; MEDRANO M.; PUERTAS A; PIERMARIA, J; DUEÑAS M T; ABRAHAM A G

San Miguel de Tucumán

Simposio; IV Simposio Internacional de Bacterias Lácticas (SIBAL); 2013

Some lactic acid bacteria (LAB) isolated from kefir grains, exert the ability to develop ropy colonies when growing in MRS-Agar, that could be associated to exopolysaccharide (EPS) producing bacteria. EPS producing LAB have the ability to synthesize in situ these biopolymers, which could act as natural thickening agents, improving texture on fermented products. This ability, and the GRAS status that LAB possesses, confers these microorganisms an additional value to be used on dairy industry. The aim of the present study was to conduct a genotypic and phenotypic characterization of the EPS production of 3 Lactobacillus paracasei strains (CIDCA 8339, CIDCA 83123, CIDCA 83124) and 2 L. kefiranofaciens strains (CIDCA 83118, CIDCA 83119) isolated from kefir grains. For genotypic characterization, the presence of the priming enzyme glycosyl transferase (pGT) -essential for heteropolysaccharides synthesis- was determined by PCR. The obtained products were amplified and sequenced, finding that the pGT gen was present in all the studied strains. For phenotypic characterization, all the microorganisms were grown in milk under their respective optimal culture conditions, and EPS production was characterized. EPS produced by these strains was between 140 and 301,9 mg/l. Molecular weight of EPSs was determined by high pressure liquid chromatography (HPLC) using a molecular exclusion column associated to a refraction index detector. Different fractions were found, with molecular weights between 104-106 Da for EPSs produced by L. paracasei and 102-105 Da for those produced by L. kefiranofaciens. To conduct all the determinations, two EPS producing strains were used as positive controls: L. delbrueckii subsp bulgaricus CIDCA 332 and L. kefiranofaciens subsp kefiranofaciens JCM 6985. The evaluation of the flow curves of the fermented products of all the studied strains showed a pseudoplastic fluid behavior, and presented apparent viscosity values and hysteresis areas higher to acid milk gels obtained by chemical acidification of milk with δ-gluconolactona. It can be concluded that Lactobacillus studied possess the gen encoding enzyme responsible for heteropolysaccharide synthesis. The phenotypic expression of this gen results in the production of EPSs that modify rheological behavior of fermented milks. Taking into account the present results these strains and the EPSs they produce are interesting candidates for their application in food industry