Stabilization of rice bran using ohmic heating or ultra-superheated steam

Abstract

Rice bran (RB) is stabilized to improve its quality and extend its shelf life. RB stabilization reduces lipases, peroxidase, lipoxygenases and auto-oxidation enzymatic activities to prevent rancidity. This study investigated the effects of ohmic heating (OH) or ultra-superheated steam (USS) treatments on the free fatty acid (FFA) content and lipase activity (LA) compared to a hot-air (HA) oven during 15 d of storage in open containers at room temperature. After 15 d, the FFA level of the untreated RB was 23.55%, while the FFA levels for the RB subjected to HA for 15 and 90 min were 12.40% and 7.82%, respectively. On the other hand, the FFA levels for the RB subjected to OH at 100°C for 15 min and USS at 400°C for 25 s were 3.91% and 4.71%, respectively, and were considered suitable for industrial purposes (FFA< 5%) in edible oil extraction. A low LA (< 0.1 international units per gram of RB (IU/g RB)) was observed in the RB treated using the OH or USS treatments, whereas an LA range of 0.654–1.051 IU/g RB was detected for HA. The OH and USS treatments effectively inactivated LA and inhibited FFA formation in shorter heating times, compared to HA. OH-applied electricity as the heating source had rapid and uniform energy conversion that might be advantageous compared to HA. USS used very high temperatures for short times with high throughput. In conclusion, OH at 100°C for 15 min and USS at 400°C for 25 s were recommended for effective RB stabilization.