Abstract

Total phenolic compounds (TPC), total flavonoid contents (TFC) and antioxidant activity of extracts from 8 varieties of Chinese and Thai rice grains were evaluated. Extraction was done using water (at 25°C), hot water (at 50°C) and 70% ethanol. Highest TPC and TFC were seen in all rice varieties after extraction with 70% ethanol. The Heimi variety of Chinese rice showed the highest TPC and TFC (634.83 and 158.47 mg/kg, respectively) followed by Jing Nian variety, also from China, Dok Kam and Niaow Deang varieties both from Thailand, respectively. Highest antioxidant activity was observed in Heimi followed by Jing Nian, Dok Kam and Niaow Deang varieties. The color of Heimi and Jing Nian is black, and that for Dok Kam and Niaow Deang is red, so TPC and TFC were correlated with the color of rice. However, no correlation was observed with the Nang Dum variety from Thailand even though it has a black color. Its TPC and TFC were found to be statistically the same as that of the white-colored Ji Nong Da, T-You 597 and Xiang Wan Nuo 1 Hao varieties from China. Antioxidant activities from each solvent system extraction (water, hot water and 70% ethanol) were also found to be directly correlated with the quantity of TPC and TFC. The TPC had positive correlations with DPPH scavenging (R² = 0.9155, 0.9358 and 0.9625), reducing power (R² = 0.9799, 0.8521 and 0.9733) and inhibition of lipid peroxidation (R² = 0.7621, 0.7429 and 0.9610). TFC also had positive correlations with DPPH scavenging (R² = 0.9098, 0.9246 and 0.9477), reducing power (R² = 0.9916, 0.9745 and 0.9844) and inhibition of lipid peroxidation (R²= 0.7548, 0.7178 and 0.8283), respectively.

Key words: Rice grain, bioactive compounds, total phenolic, flavonoids, antioxidant component.