The application of L‐glutaminase for the synthesis of the immunomodulatory γ‐D‐glutamyl‐L‐tryptophan and the kokumi‐imparting γ‐D‐glutamyl peptides

Glutaminase of Bacillus amyloliquefaciens has been used to synthesize the immunomodulatory γ-D-glutamyl-L-tryptophan (γ-D-Glu-L-Trp) and the kokumi-active γ-D-glutamyl peptides. The optimum yield of γ-D-Glu-L-Trp was 55.76 mM in corresponding to a minimum yield of by-product (γ-D-Glu-γ-D-Glu-L-Trp) in the presence of 75 mM D-Gln and 100 mM L-Trp. The glutaminase has a low Km values for the donors (D-Gln and L-Gln:5.53 and 0.98 mM), but high ones for the acceptors (L-Trp, L-Phe, L-Met, L-Val and γ-[D-Glu](n=1,2,3)-L-Val/L-Phe/L-Met, ranging from 32.51 to 193.05 mM). The highest Km value appearing when n = 2 (γ-[D-Glu](n=0,1,2)-L-Val/L-Phe/L-Met) suggested the rising difficulty for synthesis when the number of donor increases in the reaction mixtures. The γ-[D-Glu](n=1,2,3)-L-Val/L-Phe/L-Met at 5 mM can impart the blank chicken broth an enhancing monthfulness, thickness, and umaminess taste.