Effect of polishing and cooking on the antioxidant activities of local rice

Abstract

The effect of polishing and cooking on the antioxidant activities of local rice was studied. Brown rice was polished to 2%, 4% and 6% of polishing degree using embryo rice machine to produce three levels of embryo rice. All rice sample (brown rice, embryo rice 1 (2%), embryo rice 2 (4%), embryo rice 3 (6%) and white rice) were cooked using electric rice cooker. The raw and cooked rice samples were analyzed for antioxidant by total phenolic content (TPC), ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays. Polishing degree and cooking treatment showed significant (p≤ 0.05) effects on both antioxidant activities (TPC, FRAP and DPPH radical scavenging values) of the raw and cooked rice samples. Results showed that raw brown rice and raw embryo rice 1 were significantly higher than the other type of rice samples for TPC and FRAP values. In DPPH radical scavenging activities, raw brown rice had the highest value while white rice indicated the otherwise. Cooked brown rice demonstrated significantly higher of FRAP values (p≤ 0.05) than embryo rice 1, followed by embryo rice 2, embryo rice 3 and white rice. No significant differences were observed either between TPC values of cooked brown rice and cooked embryo rice 1 or between the DPPH radical scavenging values of cooked embryo rice 2 and cooked embryo rice 3. High positive correlations were determined between TPC, FRAP and DPPH assays (R2 > 0.70) of the samples. In overall, moderate level of antioxidant activities were detected in the raw and cooked rice samples.