Abstract
A simple method was developed for determining γ-aminobutyric acid (GABA) in rice by using HPLC with fluorescence detection. GABA was extracted with a 75% ethanol solution, and then converted with fluorescamine acetone (3 mg/ml) and a 0.2 M borate-sodium hydroxide buffer solution (pH 9.0). GABA was separated in a reversephase Cosmosil 5 C 18-MS II column (4.6 mm i. d. ×times;25 cm) by using a 30: 70 acetonitrile-0.01 M sodium acetate mixture at pH 6.6 containing 5 mM tetra-n-butylammonium bromide as the mobile phase, and determined by fluorescence detection (excitation at 390 nm, emission at 480 nm). The detection limit was 0.1 μg/ml.
The contents of GABA in brown and milled rice samples (raw and cooked) were then determined by this method. The contents of GABA in Nara-hinohikari, Niigata and Kyoto-koshihikari brown rice samples were in the range of 31-41 μg/g dry weight, while those in well-milled rice samples were 13-18 μg/g dry weight. The GABA content in a half-milled rice sample was higher than that in a well-milled one, and after being cooked, the former was 1.5 times the latter. This result suggests that half-milled rice would be an efficient supply source of GABA in daily foods.
