Development of Enzymatic Synthesis of gamma-Glutamylcarnosine and Its Effects on Taste

gamma-Glutamyl peptides have amide bonds between the gamma-carboxy group of glutamic acid and the amino group of amino acids or peptides. Some of these gamma-glutamyl peptides are known as kokumi substances. Kokumi substances enhance the taste, mouthfulness, thickness, and continuity of the dish. gamma-Glutamylcarnosine (gamma-L-glutamyl-beta-alanyl-L-histidine) is a gamma-glutamyl peptide, and this peptide has been suggested as a kokumi substance; however, its effects on taste have not been evaluated directly. As gamma-glutamylcarnosine is not available commercially, the conditions for its enzymatic synthesis using a gamma-glutamyltranspeptidation reaction of gamma-glutamyltranspeptidase of Escherichia coli was optimized. The synthesized peptide was purified with a Dowex 1 x 8 column, and its structure was identified by mass spectrometry and NMR spectroscopy. This is the first report of the enzymatic synthesis of gamma-glutamylcarnosine. Using this purified preparation, its effects on the sense of taste were investigated. However, the effects of gamma-glutamylcarnosine on the sense of taste were not detected except for increased bitterness.