Antioxidant components and properties of five long-grained rice bran extracts from commercial available cultivars in Thailand

Five varieties of long-grained rice bran, which are the most commonly cultivated varieties in Thailand, are abundant in antioxidant components. The antioxidative activity of rice bran extracts was investigated using various established in vitro systems, including 2,2′-diphenyl-1-picrylhdrazyl free radical-scavenging (DPPH^{{radical dot}}), total reducing power, ferrous ion-chelating activity and lipid peroxidation inhibition. The total phenolic and flavonoid contents, and gamma-oryzanol, tocopherol and tocotrienol isomer contents of rice bran extract were also determined by colorimetric assay and high performance liquid chromatography. The methanolic rice bran extracts produced strong results with DPPH free radical-scavenging (EC₅₀ 0.38-0.74 mg/ml), reducing power (EC₅₀ 0.10-0.53 mg/ml), ferrous ion-chelating activity (EC₅₀ 0.11-0.55 mg/ml) and inhibition of lipid peroxidation (EC₅₀ 0.14-0.57 mg/ml). Total phenolic and flavonoid contents, and gamma-oryzanol, tocopherol and tocotrienol contents of rice bran extract were in the range 2.2-3.2, 0.03-0.10, 0.56-1.08, 0.35-0.77 and 0.22-0.46 mg/g rice bran, respectively. These results indicated that the methanolic components of the long-grained rice bran extracts might potentially be natural antioxidants.