Effect of various heat treatments on rancidity and some bioactive compounds of rice bran

Abstract

Rice bran contains natural phytochemicals but unstable against hydrolytic and oxidative rancidity. Various heat treatments, such as dry-heating (DH), freeze-drying followed by dry-heating (FDDH), microwave heating (MH), autoclaving (AC), and ethanol vapor (EV) treatment were applied to rice bran and their effects on the storage stability at room temperature were evaluated. The free fatty acid (FFA) content of untreated rice bran gradually increased from 2.14 to 19.81% during 24 weeks, whereas those of the treated rice brans were not or marginally changed. The FFA content in DH samples was greater than that in FDDH samples, indicating the positive effect of freeze-drying prior to DH. Among the treatments, autoclaving was most effective in retarding the FFA formation. The tocol content in the rice brans varied with the treatments, ranging from 181.4 mg/kg (EV) to 310.6 mg/kg (AC), whereas that in untreated rice bran was 216.3 mg/kg. Amounts of other bio-functional components such as phytosterols and policosanols were either unchanged or increased by the treatments. Policosanol level was increased by all the heat treatments, but not affected by EV treatment, indicating that the thermal treatments induced the release of free policosanols. (C) 2014 Elsevier Ltd. All rights reserved.