Influence of extraction and pretreatment conditions on the yield, solubility, and quality of rice bran oil extracted with CO2-expanded hexane

Abstract Efficient, low-cost methods are required to produce impurity-free bio-oils with minimal nutrients depletion. This study investigated the effect of extraction and pretreatment conditions on the quality of rice bran oil extracted with CO2-expanded hexane. The extraction conditions considered were temperature (20–30°C), CO2 mole fraction (0.76–0.94), and pressure (4.2–7.0 MPa). The effectiveness of rice bran hot air drying at 80–100°C for 0.5, 1, 3, and 5 h for lipase inactivation was also studied. The rice bran oil yield and the content of free fatty acids did not depend significantly on the extraction temperature or pressure. The oil solubility increased significantly (p < 0.05) with every 5°C increment while decreasing significantly at pressures below 5.0 MPa. The optimum extraction conditions for phosphorus-free rice bran oil (phosphorus concentrations of 9.8, 9.1, and 6.2 ppm) were CO2 mole fraction of 0.82 at 5.1 MPa and 20°C, CO2 mole fraction of 0.87 at 5.0 MPa and 25°C, and CO2 mole fraction of 0.92 at 5.1 MPa and 30°C, respectively. The most effective pretreatment conditions for rice bran before storage for 10 weeks were 100°C for 1 h. In addition, the phosphorus concentration of rice bran oil extracted with CO2-expanded hexane at a CO2 mole fraction of 0.88, 5.1 MPa, and 25°C was ≤ 7.00 ppm, regardless of the pretreatment conditions. Therefore, CO2-expanded hexane extraction can be potentially used to produce impurity-free rice bran oil from both treated and untreated rice bran without refining.