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.
Highlights
Antioxidants for oxidative stress protection from natural sources such as grain crops, vegetables and fruits are becoming a profitable alternative as compared to synthetic antioxidants that have adverse effects
BB rice, a black rice variety from China, contained the highest Total phenolic compounds (TPC) from all the solvents extraction. These data indicate that black rice has higher total phenolic compound than red and white rice, which is similar to those reported by Muntana and Prasong (2010) that high phenolic compounds can be found in pigmented rice such as red and black rice
In all (Chinese and Thai) varieties of rice used in this study, ethanol was shown to be the best solvent for extracting phenolic compounds, while the least effective was the use of water (25°C)
Summary
Antioxidants for oxidative stress protection from natural sources such as grain crops, vegetables and fruits are becoming a profitable alternative as compared to synthetic antioxidants that have adverse effects. Free radicals have been claimed to induce oxidative stress in various cell components including proteins, lipids and DNA, leading to certain diseases such as cancer, cardiovascular diseases and ageing and inflammatory diseases. Rice (Oryza sativa Linn.) is the most important cereal crop in the world, either directly as human foods or indirectly as animal feeds. Rice is one of the main food and source of nutrition for most of Thai population. Rice is rich in many nutrient components including carbohydrates, proteins, certain fatty acids and micronutrients
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