Identification and Quantification of the Kokumi Peptide, γ-Glu-Val-Gly, in Foods

The potent kokumi peptide, γ-glutamyl-valyl-glycine (γ-Glu-Val-Gly), was identified and quantified in various foods using high-performance liquid chromatography-tandem mass spectrometry. Among the raw and cooked foods tested, γ-Glu-Val-Gly was detected and quantified in raw and dried scallops at 0.26 and 2.5 μmole/kg, respectively. Cooked king prawns were previously reported to contain γ-Glu-Val-Gly at 0.60 μmole/kg. This peptide was present at higher concentrations in various fermented foods, such as fish sauces, soy sauces, and fermented shrimp pastes, than in raw and cooked foods. γ-Glu-Val-Gly was also detected and quantified in beer and cheese. The concentrations of γ-Glu-Val-Gly in the fermented seasonings, foods, and beverages tested were as follows: fish sauces, 1.3–41.4 μmole/L; soy sauces, 4.9–20.1 μmole/L; fermented shrimp pastes, 3.2–17.1 μmole/kg; beer, 0.26–0.59 μmole/kg; cheese made from ewe’s milk, 1.2–1.9 μmole/kg. γ-Glu-Val-Gly positively correlated with the quality grade of dark-colored soy sauce (correlation coefficient ρ = 0.810, p < 0.05). These results suggest that γ-Glu-Val-Gly is widely distributed in foods, particularly in fermented foods, and also that the concentration of this peptide has potential as an indicator of the sensory quality of fermented foods.