Antioxidant activities, total phenolic and flavanoid content in selected sarawak rice varieties using aqueous-based extraction technique / Muhammad Faisal Ikhwan Othman

Plant-derived metabolites compounds known as phytochemicals which comes from foods such as cereals, beans, botanicals and beverages made from plants such as tea and wine are considered to playa major role in protecting human against diseases. Certain rice varieties contain concentrated pigment such as anthocyanidin or proanthocyanidin in the rice bran layer which contributed to different colors of rice and reported with high antioxidant activity depending on the content of phenolic compounds. In Sarawak, there are over 100 indigenous rice varieties with different colors that were produced by the locals with different colors but less scientific attention has been carried out on its health potential. This study aimed to determine the antioxidant activities, total phenolic content and total flavonoid content of selected Sarawak rice varieties using aqueous-based extraction technique. The rice samples were extracted using distilled water at 60 - 60°C for 6 hours and the rice extracts were analyzed for their antioxidant activity using DPPH radical scavenging and ferric reducing antioxidant potential (FRAP) assays as well as their total phenolic and total flavonoid content. In this study, CU demonstrated the highest scavenging activity (47.37 ± 1.09), followed by BP (22.62 ± 2.41), BR (11.90 ± 0.11), MU (10.92 ± 0.50), WK (10.08 ± 0.75) and BM (4.68 ± 0.38). BR demonstrated the highest ferric reducing antioxidant potential (0.27 ± 0.02), followed by WK (0.17 ± 0.01), MU (0.16 ± 0.01), BM (0.11 ± 0.02), CU (0.11 ± 0.04) and BP (0.05 ± 0.01). The results obtained for both total phenolic and flavonoid content were similar in the following order WK>MU>CU>BM>BP with BR exhibiting the highest total phenolic and flavonoid content (188.33 ± 6.76 and 229.33 ± 16.59 respectively). Pearson's correlation analysis demonstrated that DPPH was weakly correlated with both total phenolic as well as total flavonoid content (r = 0.287 and 0.317, respectively, P < 0.01) whereas significant correlation was seen between FRAP and both total phenolic and flavonoid content (r = 0.932 and 0.966, respectively, P < 0.01). CU and BR rice exhibited significantly higher antioxidant activities and contained higher polyphenolic contents compared to other rice samples used in the study. Significant ferric reducing antioxidant potential activity of BR rice was largely contributed by the total phenolic and total flavonoid contained in the rice. BP rice showed the lowest value for FRAP, total phenolic and total flavonoid contents whereas BM rice showed the lowest value for DPPH assay.