Preparation Of Rice Bran Oil And Studies Of Its In Vitro Antioxidant Activity

In the present study, regular and selenium-enriched rice brans were used as experimental materials. Firstly, the microwave heating parameters of rice bran samples were optimized, and raw and stabilized rice bran samples were compared during the storage. Secondly, the optimum extraction conditions of rice bran oil from both materials were obtained through an orthogonal design by supercritical carbon dioxide extraction (SC-CO₂), and in vitro antioxidant activities of the resulting extracts were investigated. Finally, comparisons of the physiochemical properties and the fatty acid compositions were conducted by refining method between refined rice bran oils and crude rice bran oils. The results were shown as follows:1. The microwave heating parameters of rice bran samples were optimized by choosing the key factors, including power, time and thickness. The optimized parameters for microwave heating of the regular and selenium-enriched rice bran were as follows: power 1000 W, time 90 s, thickness 20 mm. Among these factors, time and power were the main factors influencing the microwave stabilization.2. The effect of microwave heating on storage characteristics of stabilized and raw samples was studied during the storage times. The results indicated that free fatty acid levels (FFA) of stabilized samples were significantly lower than that of raw samples with time prolonged. And the lowest FFA levels of < 11% were observed in the stabilized samples when stored in the refrigerator (0-5℃). However, chilled storage (0-5℃) did not significantly inhibit the lipase activity and prevent the rancidity of rice bran.3. The main factors influencing extraction yield by supercritical carbon dioxide extraction ranged in the following order: extraction pressure > extraction time > extraction temperature > CO₂ flow rate. The highest yields of regular and selenium-enriched rice bran oil reached 15.62% and 20.78%, respectively. Taking the equipments and cost into account, the optimized parameters for both regular and selenium-enriched rice bran oil were: extraction temperature 45℃, extraction pressure 35 MPa, CO₂ flow rate 45 kg h^-1 and extraction time 90 min.4. Antioxidant capacity of crude rice bran oil were evaluated by the scavenging DPPH radical and the lipid peroxide inhibition. Regular rice bran oil exhibited higher ability of scavenging DPPH radical in contrast with selenium-enriched rice bran oil. However, there were no significant differences on lipid peroxide inhibition between regular and selenium-enriched rice bran oil as well asα-tocopherol.5. Based on selenium content, it was concluded that selenium was not retained in the extracts but in the remains. Therefore, the selenium did not significantly contribute to antioxidant activity of rice bran oil. Moreover, the oryzanol content of regular rice bran oil was significantly higher than that of selenium-enriched rice bran oil, and the oryzanol of the SC-CO₂ extracts was higher than that of the Soxhlet extracts.6. The FFA levels of refined regular and selenium-enriched rice bran oil ranged from 0.5 to 1.0 mg KOH/g after refining process (degumming, dewaxing and deacidification). The contents of gum & wax and phosphrous were significantly decreased. In conclusion, the quality of refined rice bran oil was improved, which was mainly attributed to the increased unsaturated fatty acid and decreased saturated fatty acid contents.