Quantification of γ-glutamyl-α-aminobutyric acid (γ-Glu-Abu) in beer by LC/MS/MS using stable isotope dilution

Abstract

The quantification of the kokumi peptide, γ-glutamyl-α-aminobutyric acid (γ-Glu-Abu) in commercial beer was conducted. An analytical method using high-performance liquid chromatography-tandem mass spectrometry (LC/MS/MS) after a derivatization with 6-aminoquinoyl-N-hydroxysuccinimidyl-carbamate (AQC) was constructed. A stable isotope, γ-Glu (UL[uniformly labeled]- 13 C, 15 N)-Abu was used as an internal standard for quantification. The detection of the AQC-derivative of γ-Glu-Abu was achieved by MS/MS using a multiple reaction monitoring (MRM) method. The coefficient of variation (CV) of analytical results of 1 µM γ-Glu-Abu solution (n = 6) was 1.65%. The recovery was assessed by analyzing the beer samples in which 0.1 µM γ-Glu-Abu was spiked, and the average recovery was 94%. These results suggest that this method enabled the precise and repeatable quantification of γ-Glu-Abu. All kinds of beer including Lager type and Ale type contained γ-Glu-Abu, and the contents varied from 12.5 µg / L to 24.0 µg / L (0.054 µM to 0.103 µM). These results suggest that γ-Glu-Abu is distributed in beer, and this study represents the first report documenting the content of γ-Glu-Abu in brewed alcoholic beverages.

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