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 gamma-glutamyl peptides. Aspects covered include food sources of the peptides, their enzymatic synthesis, activation on the kokumi receptors, and functional properties. gamma-Glutamyl peptides, including gamma-glutamyl dipeptides, tripeptides, and sulfur-containing gamma-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 [gamma-Glu]((n <= 5))-Phe/Val/Met/Tyr/Leu/His/Tau, gamma-glutamyl-S-allyl-cysteine and gamma-glutamyl-S-methyl-cysteine, have been successfully synthesized via catalysis with gamma-glutamyl transpeptidase and L-glutaminases. These kokumi-active gamma-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 gamma-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 gamma-glutamyl peptides in tissues.