Antioxidant capacities and polyphenol content of colored rice cultivars

Abstract

Antioxidant capacities of nine rice cultivars (four red rice, four purple-black rice and Koshihikaris) were evaluated in terms of oxygen radical absorbance capacity (ORAC) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging ability. All colored rice extracts showed significantly higher total ORAC (58.0-169.4 μmol of Trolox equivalent (TE) per gram dry weight) and DPPH radical scavenging abilities (10.8-52.2 μmol TE/g-dry weight) than those of extracts from .Koshihikaris (24.9 and 2.5μmol TE/g-dry weight, respectively). Total polyphenol content of rice extracts was measured using Folin-Ciocalteu assay, and showed highly positive correlations with hydrophilic (H)-ORAC (r=0.984, p<0.01) and DPPH radical scavenging abilities (r=0.948, p<0.01). Both contents of proanthocyanidin in red rice and anthocyanin in purple-black rice were associated with H-ORAC, DPPH radical scavenging ability and total polyphenol content in the colored rice groups. In addition, a strong correlation (r=0.946, p<0.01) was also found between H-ORAC and DPPH radical scavenging ability. Five cultivars of colored rice were subjected to the evaluation for 2 harvest years to investigate differences between different crop years. Although antioxidant capacity and polyphenol content values were different between the 2 crop years, the order of the values among the cultivars remained mostly unchanged. These results indicate that colored rice is a potential bio-functional food with high antioxidant capacities, which is due mainly to polyphenols in the rice.