Free D- and L-Amino Acids from Hydrolyzed Milk Proteins by Pseudomonas fluorescens ATCC 948

¹ Department of Food Science, Technology and Nutrition, University of Perugia, Perugia, Italy

Cell-associated peptidase activity of Pseudomonas fluorescens ATCC 948 was studied on hydrolyzed milk proteins. The substrate was produced by treatment of the UHT skim milk with neutral endoprotease B500. The cell-associated peptidase activity was determined by gas chromatographic analysis of free D- and L-amino acids. The total free amino acids were higher when the cell-associated peptidases acted on hydrolyzed milk proteins (202.8 µg/ml) rather than on unhydrolyzed skim milk (63.9 µg/ml). Glutamic acid (65.1 µg/ml), Leu (36.9 µg/ml), and Ala (16.5 µg/ml) were the most abundant. Concentrations of D-amino acid isomers (28.3 and 3.7 µg/d for D-Glu and D-Ala, respectively) also were high. Hydrolysis of the dipeptide L-leucyl-L-leu was 61% but was minimal for the other D- and L-configurational isomers of the dipeptide.

Key Words: Pseudomonas fluorescens • peptidases • bitter taste • D-amino acids

Submitted on August 12, 1992
Accepted on March 17, 1993