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Comparison of Classical Ion Exchange Amino Acid Analysis and o-Phthaldialdehyde Methods to Characterize Proteolysis by Lactobacillus bulgaricus¹

Department of Nutrition and Food Sciences, Utah State University, Logan 84322-8700

ABSTRACT

Seven strains of Lactobacillus bulgaricus were assayed for proteolytic activity using o-phthaldialdehyde and classical ion exchange amino acid analysis. The strains were ranked in the same order of proteolysis by both methods. Linear regressions of total and individual amino acid concentrations, except for alanine and glycine, were correlated with o-phthaldialdehyde results (R² = .95). The mean coefficient of variation was 7.3% for amino acid analyses and 10.2% for o-phthaldialdehyde. The o-phthaldialdehyde method was comparable to amino acid analysis for measuring gross proteolysis, but amino acid analysis provides additional information.

¹ Contribution Number 3786 of the Utah Agricultural Experiment Station. Approved by the director. Mention of companies or products does not constitute endorsement by Utah State University, Utah Agriculture Experiment Station, or Weber State College over similar products not mentioned.

² Department of Microbiology, Weber State College, Ogden 84408-2506.