Improvement of the Bitter Taste of Amino Acids through the Transpeptidation Reaction of Bacterial γ-Glutamyltranspeptidase

The tastes of several bitter amino acids and their γ-glutamyl derivatives were compared. The bitterness of Phe, Val, Leu, and His was reduced, sourness was produced, and preferences were increased by γ-glutamylization. Because the effect of γ-glutamylization of bitter amino acids was most obvious for Phe, which is an atypical bitter amino acid, an enzymatic method for the synthesis of γ-glutamylphenylalanine (γ-Glu-Phe) involving bacterial γ-glutamyltranspeptidase was developed. The optimum reaction conditions were 200 mM Gln, 200 mM Phe, and 0.5 unit/mL GGT, pH 10.4. After 1.5-h of incubation at 37 °C, 140 mM γ-Glu-Phe was obtained, the yield being 70%. γ-Glu-Phe was purified on a Dowex 1x8 column and then identified by NMR. Keywords: γ-Glutamyltranspeptidase; γ-glutamyl amino acid; γ-glutamylphenylalanine; bitter taste; enzymatic synthesis