CONICET | Buscador de Institutos y Recursos Humanos

Human breast milk has been recently proposed as a source of lactic acid bacteria with probiotic potential for specific uses: the supplementation of infant formulas with the microbiota normally transferred from mother to child via breast milk during the first days of life after birth. The supplementation of infant formulas with this kind of strains and at the right doses could be useful to beneficial and transiently modify the intestinal microflora of newbornes that, for certain reasons, cannot be exclusively breast-fed. However, little information is available about the culturability, conservability and technological performance of LAB isolated from breast milk. In our laboratory, we isolated 6 bifidobacteria strains (B. animalis subsp. lactis) from 16 lactating mothers between days 1 and 12 after delivery. The aim of this work was to study the technological potencial for their use in dairy products. We studied: 1) the capacity of growth in 10% milk supplemented with (0, 0.05, 0.1, 0.25 or 0.5% yeast extract); 2) resistance to the frozen storage in 20% milk (-20 and -80ºC, 6 months); 3) resistance to spray drying in 20% milk (mini-spray Buchi B-290) and during the cold storage of the powders (5 and 25ºC, 6 months); 4) resistance to the cold storage (5ºC) in 10% milk (pH 6.0 and 4.5, 4 weeks); 5) thermal resistance during the rehydratation in hot water (40º, 50º and 60ºC, 60 min) of the spray dried powders and 6) resistance to gastric digestion (continuous drop of pH from 5 to 2.2 during 90 min in HCl-pepsin solution at 37ºC) and bile salts (0.3 and 0.5%). Two of the strains gradually lost their culturability and were no longer studied. The rest of the strains showed the capacity to grow in milk only in the presence of yeast extract. Cell suspensions (109 CFU/ml) showed good resistance to the frozen storage, without significant loss in viability after 6 months. Strains were also resistant to the spray drying process. Spray dried powders (moisture < 4%) contained approximately 109 CFU/g. Cell viability was very satisfactory in powders maintained at 5ºC whereas in those stored at 25ºC, losts in cell viability were observed (from 2 to 5 log orders). Strains showed stability in acidified milk for 4 weeks at 5ºC (losts in cell counts < 0,5 log orders). No losts in cell viability were observed in powders rehydrated in hot water (simulation of the preparation of nursing bottles) up to 50ºC for 60 min. At 60ºC, the losts in cell viability were higher than > 4 log orders. The strains also showed a high tolerance to simulated gastric digestion (losts in cell counts < 1 log order) and the capacity to grow in the presence of physiological concentrations of bile salts. We concluded that bifidobacteria isolated from human breast milk have, in a strain dependant way, a promising potencial for the development of dairy products for specific uses.