Comparative Studies on Peptidases of Lactobacillus casei Subspecies

Abstract

The objective of this study was to isolate strains of lactobacilli containing peptidases of high specific activities and wide spectrum specificities for the enzyme modification and accelerated ripening of Cheddar cheese. Six selected strains of Lactobacillus casei (ssp. casei, ssp. pseudoplantarum, and ssp. rhamnosus) were evaluated for their amino-, di-, tri- and carboxypeptidase activities using 30 different synthetic peptides and peptide derivatives. All six strains showed similar substrate specificities towards various peptides, except for phenylalanine-proline, which was only hydrolyzed by Lactobacillus casei ssp. casei strains. Analysis of variance revealed significant differences among strains with respect to their specific activities. Overall profiles showed that Lactobacillus casei subspecies contained high amino- and dipeptidase with relatively weak tripeptidase activities. Lactobacillus casei ssp. casei strains LLG and ATCC 393 had the highest di- and tripeptidase activities respectively, whereas Lactobacillus casei ssp. rhamnosus strain S93 contained the highest activities for leucine-, lysine-, alanine-, and valine- and methionine-aminopeptidases, and proline-iminopeptidase. The dipeptidases of all six strains exhibited 8 to 10 times higher affinity for alanine-X dipeptides. Highest activities for amino- and dipeptidases were observed with leucine p-nitroanilide (256 μmol/min per mg of protein) and alanine-methionine (4976 absorbance units/min per mg of protein) as substrates. Lactobacillus casei ssp. casei strains showed strong activities against bitter peptides (phenylalanine-proline, proline-phenylalanine, proline-isoleucine) and sulfur-containing amino and peptide derivatives (methionine p-nitroanilide, cysteine p-nitroanilide, and alanine-methionine), which are of great importance in removing bitterness from and in ripening of cheeses. None of the strains showed any detectable carboxypeptidase activity when tested on seven carboxyl end-substituted peptides. © 1990, American Dairy Science Association. All rights reserved.