Gamma glutamyl peptides: The food source, enzymatic synthesis, kokumi-active and the potential functional properties – A review

This review covers recent developments in kokumi taste (thickness, richness, mouthfulness, and continuity) studies of γ-glutamyl peptides. Aspects covered include food sources of the peptides, their enzymatic synthesis, activation on the kokumi receptors, and functional properties. γ-Glutamyl peptides, including γ-glutamyl dipeptides, tripeptides, and sulfur-containing γ-glutamyl-S-alk(en)yl-l-cysteine, are widely found in edible legumes, alliaceae, and fermented foods like soy sauce and cheese. These peptides, including [γ-Glu](n≦5)-Phe/Val/Met/Tyr/Leu/His/Tau, γ-glutamyl-S-allyl-cysteine and γ-glutamyl-S-methyl-cysteine, have been successfully synthesized via catalysis with γ-glutamyl transpeptidase and L-glutaminases. These kokumi-active γ-glutamyl peptides exhibit astringency only in aqueous solution, but kokumi-imparting properties result when the peptides are added to food. Several of these peptides exhibit certain basic tastes, including sourness, bitterness, or umaminess in aqueous solution, and some can enhance the intensity of the basic taste. Several γ-glutamyl peptides can aid the treatment of intestinal inflammation for the positive allosteric activation on the calcium-sensing receptor. Future areas of research include further investigation of sensory physiology, screening microbial enzymes with high affinity for different acceptors, functional properties like triggering the release of cholecystokinin via the activation of the calcium-sensing receptor, and metabolic mechanism of the exogenous γ-glutamyl peptides in tissues.