G. S. De Giori

Characterization of natural isolates of Lactobacillus strains to be used as starter cultures in dairy fermentation.

The technological relevant characteristics of five homofermentative lactobacilli strains, isolated from natural fermented hard cheeses, were studied. Isolates CRL 581 and CRL 654, from Argentinian artesanal hard cheeses, and isolates CRL 1177, CRL 1178, and CRL 1179, from Italian Grana cheeses, were identified as Lactobacillus delbrueckii subsp. lactis and Lactobacillus helveticus, respectively, by physiological and biochemical tests, SDS-PAGE of whole-cell proteins and sequencing of the variable (V1) region of the 16S ribosomal DNA. All strains showed high levels of beta-galactosidase activity. However, proteolytic activity varied widely among isolates. Strains CRL 581, CRL 654, and CRL 1177 hydrolyzed alpha- and beta-caseins and were able to coagulate reconstituted skim milk in less than 16 h at 42 degrees C. According to the substrate specificity, these proteinases have a caseinolytic activity comparable to that of the P(III)-type of lactococcal proteinases. No strains produced inhibitor substances (bacteriocin) and all were insensitive to attack by 14 L. helveticus- and L. delbrueckii subsp. lactis-specific bacteriophages.

Effectiveness of Soy Milk as Food Carrier for Lactobacillus Acidophilus

: Three mild-fermented milk beverages prepared from soy milk and cows milk were compared for their ability to preserve the cell viability of Lactobacillus acidophilus during refrigerated storage, in associative growth with Lactobacilus casei and Streptococcus thermophilus . The highest survival rate was obtained by using soy milk as substrate. The presence of L. casei in the starter culture had no influence on the viability of L. acidophilus , while the streptococcal cells showed a harmful effect. The culture activity measured as proteolysis and acid production remained fairly constant during the shelf life, despite the variations in colony counts observed for the different fermented milks analyzed.

L-glutamate transport in Lactobacillus helveticus

An energy source (glucose or lactose) was required for the transport of L-glutamic acid by Lactobacillus helveticus. Mg(2+), K(+) and Li(+) increased its accumulation while Ca(2+) and Na(+) decreased it. It was inhibited by NaF, indicating that ATP may be involved in uptake. Optimum transport was at pH 7.3 and 45°C. L-Glutamic acid transport showed a high degree of stereospecificity, as neither D-glutamate nor D-aspartate were active. Proton-conducting uncouplers, like carbonyl cyanide-m-chlorophenylhydrazone, and ionophores (nigericin, monensin and gramicidin) were strongly inhibitory. These results indicate that a proton motive force may be involved in the transport of L-glutamic acid.An energy source (glucose or lactose) was required for the transport of l-glutamic acid by Lactobacillus helveticus. Mg2+, K+ and Li+ increased its accumulation while Ca2+ and Na+ decreased it. It was inhibited by NaF, indicating that ATP may be involved in uptake. Optimum transport was at pH 7.3 and 45°C. l-Glutamic acid transport showed a high degree of stereospecificity, as neither d-glutamate nor d-aspartate were active. Proton-conducting uncouplers, like carbonyl cyanide-m-chlorophenylhydrazone, and ionophores (nigericin, monensin and gramicidin) were strongly inhibitory. These results indicate that a proton motive force may be involved in the transport of l-glutamic acid.