Availability of partially milled rice as a daily source of gamma-aminobutyric acid

We investigated the use of a high-performance liquid chromatography (HPLC) with o-phthalaldehyde fluorescence detection to simultaneously quantify γ-Aminobutyric acid (GABA), glutamate and alanine. Using this method, the column (COSMOSIL 5C18-MS-II, 4.6mm i.d.×15cm) was eluted using a linear gradient of acetonitrile and 5mM citrate buffer (pH 6.0). The GABA contents of both milled and cooked rice samples were measured, with a gradual decrease observed as the rice was milled in raw rice. However, GABA content was markedly diminished due to washing in rice milled for a longer period. In less milled rice, the GABA and glutamate contents increased when the rice was cooked without washing. As a result, the GABA content of cooked under-milled rice was twice that of cooked well-milled rice available in the market, and three times greater for under-milled cooked rice without washing. These findings revealed that partially milled rice could be utilized as a daily source of GABA.