Antioxidant efficacy of phytochemical extracts from defatted rice bran in the bulk oil system

The antioxidant compounds oryzanols, tocols and ferulic acid were identified in the methanolic extracts of defatted rice bran (DRB) by high pressure liquid chromatography (HPLC). The crude methanolic extract (CME) was partially purified by re-extraction with acetone to give an acetone extract (AE). For further purification of the acetone extract, sequential solvent extraction was employed yielding a lipophilic phase (AE-LP) with hexane and a polar phase (AE-PP) with acetone. The antioxidant potential of the DRB extracts and their phytochemical constituents in bulk oils were evaluated using the Schall oven test (SOT) and differential scanning calorimetry (DSC). The extracts were effective in inhibiting lipid oxidation as assessed by peroxide value, diene value and p-anisidine value. The activity of the extracts with respect to the inhibition of primary oxidation products followed the order AE-PP > AE-LP = AE > CME with the activity of AE-PP being equivalent to that of butylated hydroxytoluene (BHT) at a 200 ppm level. However, tertiarybutylhydroquinone (TBHQ) was most active as compared to extracts and pure compounds with AE-PP showing about 45% of the activity of TBHQ at 200 ppm level. Defatted rice bran extracts proved to be effective even at the high temperature employed in DSC. The antioxidant efficacy of AE-PP was close to that of TBHQ and far greater than that of BHT at a 200 ppm level as evident from DSC results. The increase in activity with purification might be due to the enhanced levels of antioxidants in purified extracts compared to CME.