Determination of GABA Content in Thai Brown Rice by an Optimized Enzyme-based Method

Abstract

GABA content in brown rice from 32 Thai rice varieties was determined using a rapid enzyme-based method. The enzyme GABase and NADP+, which were expensive reagents used in the assay, were optimized. GABA was firstly extracted from brown rice with the optimal extraction technique using 0.3% (w/v) sulfosalicylic acid and sonication. The GABA content was then indirectly determined by the absorbance measurement of NADPH derived from enzymatic reaction of GABase. Under the optimized assay system, the enzyme-based method could accurately and economically quantified GABA when GABA concentration was in the range of 0-1.0 mM. With the GABA recovery of 92.71% evaluated by the spike recovery test, GABA in rice was precisely quantified by the optimized method. Among rice varieties that were examined, Chaw Lamud contained the lowest GABA content (7.60 mg/100 g), while RD41 contained the highest GABA content (29.46 mg/100 g). Concentration of GABA in brown rice was positively correlated with size and shape of rice grains. In conclusion, the enzyme-based method optimized in this study could be applied well for the determination of GABA from rice, and may also replace the commonly-used HPLC analysis of GABA in other raw-materials. The information on GABA content in rice obtained from this study will be useful for the production of healthy rice products.