Microwave pretreatment of defatted rice bran for enhanced recovery of total phenolic compounds extracted by subcritical water

Enhanced recovery of total phenolics (TP) from defatted rice bran (DRB) subjected to prior microwave pretreatment was achieved by subcritical water extraction (SWE). The effects of microwave pretreatment temperature (60–100 °C) and duration (0–30 min) were determined at raw material:water ratios (1:2 and 1:5) for SWE under fixed conditions. Optimal extraction was observed at 80 °C (for 10 min, at a ratio of 1:2). With pretreatment carried out under these conditions, a shorter extraction time of 10 min was required for SWE at 200 °C. Combining both optimized conditions, a TP yield of 190.4 ± 3.3 mg/g of DRB was achieved, some 55% more than was found to be extractable from un-pretreated samples. The antioxidant activity of the extract was also greater, as indicated by a corresponding decrease in IC50 from 38.8 ± 0.4 to 27.7 ± 0.5 μg/ml.