Developing GC and HPLC methods for the γ-aminobutyric acid quantification in rice samples

γ-aminobutyric (GABA) is a non-protein amino acid produced from glutamic acid, which acts as a neurotransmitter in humans playing a role in neurological functions and inhibiting chronic diseases like diabetes [1]. The consumption of GABA-rich foods and its extraction for supplements are of great interest. Chromatographic methodologies, the most widely used for GABA determination, require previous derivatization [2]. This work aimed at applying and comparing different derivatizations and chromatographic methods (gas chromatography and high-performance liquid chromatography) to separate and quantify GABA in simple ethanolic rice extracts. GABA was extracted from brown flour and rice bran of the Ariete variety using 70% ethanol for both methods. Separation and quantification were performed using GC-FID, after a BSTFA-1%TMCS derivatization, and using norleucine as an internal standard (IS) [3]. In the HPLC method, o-phthaldialdehyde (OPA) derivatization and a fluorescence detector were used. A linear regression between the relative area of IS and GABA standard solutions yielded 0.046-0.457mg/mL with an R²=0.9975 for the GC method, and 0.011-0.083 mg/mL with an R² = 0.9929 for the HPLC method. The detection limit (LOD) and quantification limit (LOQ) were 0.058 mg/mL and 0.177 mg/mL for the GC method, and 0.018 and 0.054 mg/mL for the HPLC method. Although GABA quantification by means of GC gave good results with the standards, this did not happen with rice samples. Rice samples fortified with GABA standard and norleucine were analyzed, but the obtained chromatograms showed too many interfering peaks which probably came from the extraction process. Based on these results, testing other extraction/cleaning methods for GABA quantification in rice matrices will be necessary. On the other hand, it was possible to quantify GABA using the HPLC method in rice samples, where the concentration in bran was higher (222.1 ± 19.3 mg/100g) than in brown rice (131.0 ± 3.9 mg/100g). This method also proved to be more sensitive than the GC method.