Determination of antioxidant components in rice bran oil extracted by microwave-assisted method

Rice bran oil was extracted by microwave-assisted extraction with isopropanol and hexane using a solvent-to-rice bran ratio of 3:1 (w/w). The experiments were done in triplicate at 40, 60, 80, 100, and 120 °C with a total extraction time of 15 min/sample. The oil components were separated by normal-phase HPLC and quantified with a fluorescence detector. The radical scavenging capability of the oil was tested with DPPH and was expressed as μmol Trolox Equivalent Antioxidant Activity. The increase in total vitamin E with temperature from 40 to 120 °C was 59.63% for isopropanol and 342.01% for hexane. Isopropanol was the best solvent for the extraction of γ-tocopherol and γ-tocotrienol as compared with hexane for both microwave-assisted and conventional solvent extraction. Isopropanol was better for oil yield extraction at high temperatures. Samples extracted with isopropanol at 120 °C had higher antioxidant activity. No differences in oil yield, total vitamin E, and antioxidant activity of oil was noticed between the two methods (microwave-assisted and solvent extractions), at 40 °C. No degradation of α-tocopherol was noticed during the process.