Characterization of total phenolics, antioxidant and antiplatelet activity of unpolished and polished rice varieties

Rice bran is concentrated with many bioactive chemicals including phenolics, oryzanol and vitamin E, that exert beneficial effects on human health, but it varies with polished and unpolished condition of rice bran. Thus this study was aimed to analyze the phenolic compounds and biological activities of four polished and un-polished rice varieties Glutinous (Hwasunchal), Sea tangle glutinous (Dongjinchalbyeo), Sea tangle unpolished (Odae), Unpolished (Chukang). Total 12 phenolics were separated within 30 min as compared retention time of standards in high-performance liquid chromatography. The ferulic acid was the most abundant free phenolic acid in all rice varieties. The rice bran extracts revealed strong antioxidant activity towards DPPH (EC50 100–165 mg/mL) and FRAP (EC50 6.5–9.5 mg/g). The extracts of unpolished (90 %) and sea taugle unpolished rice (58 %) showed higher inhibition as compared to glutinous (42 %) and sea taugle glutinous rice (56 %) in their effects on ADP-induced platelet aggregation. Total phenolic and flavonoid contents of rice bran extract were 35.5–68.6 and 8.6–48.6 mg/100 g for free form and 1.2–5.2 and 0.58–2.1 mg/100 g for bound form, respectively. The results indicate that the un-polished rice presented higher free and bound phenolics content than polished rice variety, also the un-polished rice revealed enhanced nutrient quality with significant antioxidant and antiplatelet activities.