Rapid gas chromatographic screening of edible seeds, nuts and beans for non-protein and protein amino acids

Abstract

Water extraction with subsequent picric acid treatment and solvent washing (ethyl acetate and diethyl ether) was employed for the rapid isolation of free amino acids from non-aqueous food samples. The isolated amino acids were subjected to N(O,S)-isobutyloxycarbonylation followed by solid-phase extraction and tert.-butyldimethyl-silylation for direct analysis by gas chromatography and gas chromatography-mass spectrometry. When the present method was applied to nineteen food samples (common beans, seeds, and nuts), seventeen protein amino acids and fifteen non-protein amino acids were simultaneously screened. Eleven non-protein amino acids including γ-aminobutyric acid, pipecolic acid, pyroglutamic acid, α-aminobutyric acid, α-aminoadipic acid, and β-alanine were tentatively identified, and four compounds assumed to be non-protein amino acids remained unidentified.