Autolysis of facultatively heterofermentative lactobacilli isolated from hard cheese

Facultatively heterofermentative lactobacilli are known to play a significant role in the maturation of hard cheeses made from raw milk. Autolysis measurements were carried out on nine strains, namely Lactobacillus casei, L. rhamnosus, L. pentosus and L. plantarum, isolated from cheese or the cheese-making environment. In aqueous systems, maximum levels of autolysis were found at pH values between 6.3 and 8.0, i.e., high above the pH of hard-type cheeses. Monovalent and divalent cations as well as organic acids in concentrations usually found in cheese increased the autolysis levels. Renaturing SDS-PAGE with denatured cells of L. casei, L. rhamnosus, L. plantarum or Micrococcus luteus as substrates revealed specific patterns of hydrolase activities containing up to 12 bands, depending both on the species and the strain under study. The results indicate that the potential towards autolysis should be considered during the selection of adjunct starter cultures.