Peptidase Profiling of Lactobacilli Associated with Cheddar Cheese and Its Application to Identification and Selection of Strains for Cheese-Ripening Studies

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Abstract
The objectives of this study were to isolate a heterogenous population of Lactobacillus spp. from commercially manufactured Cheddar cheese and characterize them via their intracellular peptidase activities. Strains of Lactobacillus casei were recovered most frequently, followed by strains of Lactobacillus plantarum and Lactobacillus brevis (tentative identity). Species were tentatively identified based upon their ability to ferment seven carbohydrates, selected for their ability to differentiate among species associated with milk. Cell-free extracts of strains representative of the lactobacilli populations of each cheese displayed higher specific activity toward hydrophobic as compared to hydrophilic dipeptides and p-nitroaniline derivatives. Generally, the order of most to least hydrolyzed was as follows: phenylalanine-isoleucine > valine-leucine .apprxeq. leucine-glycine > arginine-glycine > leucine-p-nitroaniline > arginine-p-nitroaniline > glutamic acid-tyrosine .apprxeq. proline-p-nitroaniline. Specific activities ranged from 0 to 5 pmol hydrolyzed/.mu.g protein per min for proline-p-nitroaniline up to 60 to 600 pmol hydrolyzed/.mu.g protein per min for phenylalanine-isoleucine. Significant differences (P < .05) in peptidase activities were often observed among but not within species. On the basis of all peptidase data collected for each isolate, cluster analysis placed the lactobacilli into groups that correlate well with their fermentative abilities and species classifications. Peptidase profiling may be reliable, alternative means of identifying lactic bacteria and gaining information of value in cheese ripening studies.