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 0-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 ophthaldiddehyde 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.