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