Comparison of lipid degradation in raw and infrared stabilized rice bran and rice bran oil: matrix effect

Abstract

In this study, freshly milled rice bran samples were stabilized with short-wave (peak wavelength 1.0–1.4 µm) and medium-wave (peak wavelength 2.4–2.7 µm) infrared (IR) emitters at the same conditions (IR power and process time). Half of the unprocessed and IR stabilized samples were stored in bran form and the other half was extracted with hexane and stored in the form of crude rice bran oil for 6 months at room temperature (25 °C). All samples were analyzed for free fatty acids (FFA), peroxide value (PV), conjugated dienoic acids, p-Anisidine value (p-AnV), and tocopherol and gamma-oryzanol contents throughout the storage. As a conclusion, it was found that hydrolytic lipid degradation occurs more likely in samples stored in bran form; however, samples stored in oil form was more prone to oxidative degradation. After 6 months of storage at room temperature, FFA content of the unprocessed (control) samples increased from 2 to 68.27% and 17.94% when stored in bran and oil matrix, respectively. Additionally FFA content of the IR stabilized samples which were stored in bran matrix was also higher than their counterparts stored in oil matrix. Medium-wave IR stabilization was more effective in retarding FFA increase when compared to short-wave IR stabilization. Although PV of all samples was below 10 meq oxygen/kg oil, PV and p-AnV of the samples stored in oil matrix was significantly higher than that of the samples stored in bran matrix (p < 0.05). Furthermore, storage in oil form resulted in higher loss in total tocopherol and γ-oryzanol compared to storage in bran form (p < 0.05).