Ohmic Heating-Aided Mechanical Extraction of Gamma-Oryzanol and Phytosterols in Rice Bran Oil

Abstract

The price of rice bran oil depends on the amounts of contained bioactive compounds especially oryzanol and phytosterols. The oryzanol content of rice bran oil under ohmic heating optimized at 70 V/cm, 90 °C for 3 min (27,580.75 ± 916.58 mg/kg) was higher than the control (24,908.57 ± 19.87 mg/kg). Ethanol-to-water ratio (p ≤ 0.000), medium-to-rice bran ratio (p ≤ 0.002), and electric field (p ≤ 0.028) all statistically significantly affected oryzanol content. Using water medium at low electric field (70 V/cm) produced the highest oryzanol content, while a high medium-to-rice bran ratio (1:1) resulted in the highest oryzanol content due to rapid temperature increase. Ohmic heating reduced acid value and free fatty acid content of rice bran oil and hence extended its shelf life. Ohmic heating under pressure (1 bar) was applied to elevate the boiling point and prolong the holding time, thereby obtaining higher oryzanol content (24,758.11 ± 48.96 mg/kg) than in non-pressurized rice bran oil (21,170.93 ± 42.72 mg/kg) (p ≤ 0.05). Conductivity of the medium and holding time positively correlated with oryzanol content whereas temperature had a negative correlation. Ohmic heating extraction efficiency increased with more water-soluble bioactive compounds ranking from phenolics, oryzanol, and phytosterols.