Effect of Soaking Temperature and Time on GABA and Total Phenolic Content of Germinated Brown Rice (Phitsanulok 2)

Rice grains riched in gamma-amino butyric acid (GABA) are increasingly popular, particularly in the health food market. It has a major inhibitory effect on neurotransmitter function, cancer cell and also reduces blood pressure. GABA contents in rice were investigated during germination. GABA levels in rice are influenced by many factors including the duration of seed incubating, soaking temperature, soaking time or in pre-germinated brown rice. The objective of this study was to investigate the effect of soaking temperature and time conditions on GABA content of brown rice germination. Phitsanulok 2 rice was germinated following a central composited design with different soaking temperature durations (20-40^oC) and time (60-300 min) for 10 treatments, then incubating at 25^oC for 24 hr. Physical quality, pH of soaking water, protein, GABA and total phenolic compound (TPC) content were analyzed. The results showed that GABA content and TPC increased from 6.71 mg/100g, 13.68 mgGAE/100g of dry sample (raw material) to 18.74 mg/100g, 33.95 mgGAE/100g of dry sample, respectively. Regression model showed that an increase of soaking temperature and time affected on an increase of GABA content (p≤0.05) as well as TPC. On the other hand, an increase of soaking temperature and time significantly decrease pH of soaking water (p≤0.05). The optimum conditions regarding soaking temperature and time were 33^oC for 300 min, which provided the highest GABA content (18.74 mg/100g), TPC (33.95 mg/100g) and pH of soaking water (5.7). This indicated that soaking conditions for germinated Phitsanulok 2 rice could increase the nutrition value of rice as functional food product.

Keywords: brown rice, germination, GABA, total phenolic compound, Phitsanulok 2 rice

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