Antioxidative evaluation of solvent extracts and fractions of oil refining steps from rice bran

The present work investigated the bioactive phytochemical contents (phenolics, flavonoids, oryzanol, β-carotene, tocols) and antioxidant activity of the methanolic (RBM), ethanolic (RBE), and acetone (RBA) extracts of rice bran or oil fractions from the refining steps of rice bran oil (RBO). The antioxidant activity was investigated by using five complementary in vitro methods: phosphomolybdenum assay, DPPH radical scavenging activity, H₂O₂ scavenging activity, hydroxyl radical scavenging activity, and reducing power. The antioxidant activity was found to increase as a function of extract concentration in all extracts and oil fractions. Of the solvents examined, the extract from methanol, which had the highest total phenolic content (TPC) and total flavonoid content (TFC), showed the highest antioxidant activity followed by RBE and RBA. However, the refining process of RBO reduced the bioactive components and antioxidant activity of RBO, in particular, a significant reduction was recorded after the neutralisation and deodorisation steps. The refining process caused about 68%, 75%, 49%, 68%, and 40% decrease in TPC, TFC, oryzanol, β-carotene, and total tocol contents, respectively, whereas about 50% reduction in antioxidant activity was found in almost all samples. FTIR spectral data revealed the existence of multiple functional groups in the samples. The order of antioxidant content matched well with that of the antioxidant activity of all samples. The present work thus recommends the use of rice bran or RBO for making various types of food materials, as it has high antioxidant activity that improves human health. In addition, the obtained data will help small entrepreneurs and farmers improve the refining process of RBO for better marketability.