HYNES Erica Rut
congresos y reuniones científicas
Non starter lactobacilli in Argentinean cheeses
Congreso; 13th World Congress IUFOST - Food is Life; 2006
Institución organizadora:
Non-starter lactic acid bacteria were isolated from Argentinean cheeses produced by different manufacturers, both at industrial and farm scale. The isolates were identified, classified and characterised by focusing on their biological features and their potential as probiotic organisms. Non-starter lactobacilli population was about 10exp5 CFU gexp-1 in all 1-week old cheeses manufactured with pasteurised milk. They reached 10exp7 CFU gexp-1 during the first month of ripening, and then remained more or less constant up to three months in the same cheeses. Initial lactobacilli plate count was higher in the farm cheeses manufactured with raw milk (10exp7 CFU gexp-1), but this population did not significantly increase during ripening. The morphology of the different colonies grown on MRS agar was observed, as well as microscopic characteristics of the bacteria in each type of colony. Catalase-negative isolates were retained and cultured on MRS broth; some of the isolates turned out viable but not cultivable and were discarded. A small proportion of the strains (12%) were salt-tolerant cocci (Enterococcus sp). A total of 22 lactobacilli strains were identified and characterised. Species identity was determined by carbohydrate fermentation patterns and confirmed by species-specific PCR assays. Diversity among isolates was studied by RAPD-PCR analysis. Biological features (resistance to bile, lisozyme and gastric solution, and prebiotic substrates utilization), as well as probiotic characteristics (hydrophobicity, beta galactosidase activity, bile salt deconjugation and antibacterial activity) were studied. The confirmed species identified (n=22) were: Lactobacillus casei (32% of the isolates), L. plantarum (23%), L. rhamnosus (18%), L. curvatus (14%), L. fermentum (9%) and L. perolens (4%). All strains tolerate 25 ppm lisozyme, but only 29% of them resisted 0.3% bile. After incubation in gastric solution (pH 2.0), plate counts decreased in several log orders, ranging from 3.2 to 7.0. The strains were able to grow in the presence of bile salts, but not to deconjugate them, and they fermented prebiotic substrates (specially lactulose and inuline). Hydrophobicity values were, in general, rather low (<46%). We concluded that non-starter lactic acid bacteria in Argentinean cheeses are mainly composed of lactobacilli. A high proportion of the isolated strains present interesting biological features, which uphold future studies of these organisms as potential probiotic bacteria.