Proteolytic Characterization of Lactobacillus delbrueckii ssp. bulgaricus Strains by the o-Phthaldialdehyde Test and Amino Acid Analysis

The o-phthaldialdehyde test and amino acid analysis were used to characterize proteolysis of milk proteins during growth of Lactobacillus delbrueckii ssp. bulgaricus. Thirty-four strains were incubated in sterile 10% NDM for 12 h. Extent of proteolysis as estimated by the o-phthaldialdehyde test revealed a large variance in total proteolysis. For seven strains, trichloroacetic acid filtrates of inoculated 10% NDM were analyzed by classical ion-exchange amino acid analysis. Each strain had a distinct pattern of individual amino acid concentrations. Amino acid profiles provided information about the proteolytic activity of these strains that was not available from the o-phthaldialdehyde test. Cluster analysis, based on amino acid profiles of each strain, differentiated the seven strains beyond what was possible by visual comparison of the amino acid analysis results.