Stabilization of Rice Bran by Infrared Radiation Heating for Increased Resilience and Quality of Rice Bran Oil Production

Rice bran, a by-product of rice milling, is a valuable source of rice bran oil (RBO). However, it is prone to rancidity and must be processed quickly after rice polishing. The researchers found that rice bran stabilization with infrared radiation (IR) at 125 V and 135 V for 5∼10 min. The most promising IR treatments were 125 V for 10 min and 135 V for 5 min, which resulted in the lowest lipase activity (93∼96% inhibition) and levels of γ-oryzanol and α-tocopherol comparable to those of the untreated control. However, the color of rice bran and RBO based on L*, a*, b*, and total color difference (ΔE) and Gardner-20 mm index darkened. Upon storage of rice bran at 38°C for 8 weeks, the use of these two IR treatments completely inhibited the rise in free fatty acid (FFA) content and peroxide values throughout the storage period. In contrast, the control had a pre-storage FFA more than double that of IR-stabilized rice bran, which further increased during storage and, in the 8th week, was more than 6-fold higher than the pre-storage level. γ-oryzanol and α-tocopherol slightly decreased with storage and their levels did not differ between stabilized and unstabilized rice bran. RBO color darkening was again observed, but the color lightened with storage, especially upon treatment at 135 V for 5 min. In contrast, the color of control RBO darkened with storage. Thus, IR at 135 V for 5 min was the most promising method for rice bran stabilization, based on which commercial IR treatment instruments can be developed.