For microwave-assisted extraction, hexane proved to be a better solvent for rice bran oil extraction as compared to isopropanol for extractions performed at 40 °C; hexane extracted approximately 40% more oil than isopropanol. While by increasing the temperature, hexane did not extract significantly more amount of oil, isopropanol extracted about 25% more rice bran oil at 120 °C than hexane in the same conditions. At higher temperature, isopropanol proved to be a better extraction solvent for rice bran oil. Hexane extracted large amount of α-tocotrienol at 120 °C while the increase in temperature for isopropanol was more beneficial for the extraction of γ-tocopherol. Also, isopropanol at higher temperature seems to extract more hydrophilic antioxidants which were revealed in the 78% increase of DPPH scavenging capability by increasing the temperature from 40 to 120 °C.
No significant differences in the oil yield, total vitamin E, and antioxidant activity of rice bran oil was noticed between the two extraction methods, conventional solvent and microwave-assisted extractions, at 40 °C; at shorter times it is expected that microwave extraction may perform better than solvent extraction, due to faster heating rates. The results showed that during the whole extraction process α-tocopherol was not degraded.