Determination and quantification of the kokumi peptide, γ-glutamyl-valyl-glycine, in commercial soy sauces

• The kokumi peptide γ-Glu-Val-Gly in soy sauces was determined and quantified by LC/MS/MS.
• Soy sauces contained γ-Glu-Val-Gly at 0.15–0.61 mg/dl.
• This is the first report to confirm the existence of this peptide in vegetable foods.

Recent studies have demonstrated that kokumi substances, such as glutathione, are perceived through the calcium-sensing receptor (CaSR), and screening by CaSR assay and sensory evaluation has shown that γ-glutamyl-valyl-glycine (γ-Glu-Val-Gly) is a potent kokumi peptide. In this study, the contents of γ-Glu-Val-Gly in six commercial brands of dark-coloured soy sauces, two brands of light-coloured soy sauce, and one brand of white soy sauce, were investigated by high performance liquid chromatography–tandem mass spectrometry (LC/MS/MS), followed by derivatization with 6-aminoquinoyl-N-hydroxysuccinimidyl-carbamate (AQC). The analyses indicated that γ-Glu-Val-Gly was present in all investigated soy sauces at concentrations ranging from 0.15 to 0.61 mg/dl, demonstrating that it is widely distributed in soy sauces.