An Improved Method to Determine Gamma-glutamylcysteine Content in Foodstuffs Using 4-(Aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole

An improved method to determine gamma-glutamylcysteine (γ-GC) content in foodstuffs was developed using 4-(aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole as a fluorescent reagent in high performance liquid chromatography analysis. The separation of γ-GC derivatives from L -gamma-glutamyl- L -cysteinylglycine (GSH) derivatives was drastically improved when acetic acid was added to the mobile phase instead of trifluoroacetic acid (TFA), resulting in an Rs value of 5.5 compared to an Rs value of 1.4 for TFA. In addition, the linearity, recovery, and precision of analysis were proven with the use of acetic acid in this method. Using this improved method, the γ-GC content in foodstuffs such as foie gras, chicken gizzard, wet yeast, and dry yeast could be determined. The γ-GC content in these foodstuffs was approximately 1–2 mg/100 g. This improved method appears useful for determining the γ-GC and GSH contents in foodstuffs.