Phytochemicals and antioxidant properties of solvent extracts from Japonica rice bran

The yield, major phytochemicals (oryzanols, tocopherols (T), and tocotrienols (T3)) and antioxidant properties of Japonica rice bran extracts were investigated, for illustrating the major effects from solvent property. Generally, the extract yield varied with the solvent used in the order of methanol (MeOH) > ethyl acetate (EtOAc) > hexane. In contrast to hexane extracts, both MeOH and EtOAc extracts exhibited a higher total content in phenolic compounds (∼2.5 g gallic acid equivalent/kg bran), oryzanols (1.6–1.8 g/kg bran), or tocols (126–130 mg/kg bran), and a higher T3% in tocols (24–26%). The MeOH extract (at 1 mg/ml) showed the greatest capability in inhibiting linoleic acid peroxidation (57%), scavenging DPPH radicals (93%), reducing power (78%), and Fe²⁺ chelating activity (∼1300 μg EDTA equivalent/g) than the other two extracts, partly attributed to its high antioxidant contents. It is newly found that the yield, total content in phenolic compounds, oryzanols, and tocols, and T3% in tocols of the extracts increased with increasing Synder’s polarity value in a quite good linear manner (R² = 0.923–1.000), associated with an increased solvent viscosity. This clearly suggests the potential of using Synder’s polarity value as an index in isolation of desired rice bran phytochemical extracts.