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

The technological relevant characteristics of five homofermentative lactoba cilli 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 he lveticus, 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 activit y. 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. Ac cording 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 insensi tive to attack by 14 L. helveticus- and L. delbrueckii subsp. lactis-specif ic bacteriophages. (C) 2000 Elsevier Science B.V. All rights reserved.