Supercritical fluid extraction of rice bran with adsorption on rice hull ash.

摘要

Rice bran oil was extracted using environmentally-friendly supercritical carbon dioxide at varying conditions. Experimental treatments included pressure (27.6, 41.4 and 55.2 MPa), temperature (40 and 60°C) and flow rates (25, 45 and 65 g/min) of supercritical carbon dioxide. Extracts collected at different time intervals during 4-hour extraction runs in a 3-L extractor were analyzed for oil yield and antioxidants. Normal-phase HPLC was used for analyzing the extract for important antioxidant compounds of oryzanol, tocopherols, tocotrienols. Silica rich rice hull ash adsorbent was also incorporated in combined extraction-adsorption experiments under similar supercritical fluid conditions. Supercritical extraction yields of rice bran oil and antioxidants were compared with 6 - hour Soxhlet extraction using petroleum ether solvent. Total oil extract yields for SFE (17.26-18.52%) and experiments conducted with ash (17.35-18.99%) for the extraction conditions of higher pressure (55.2 MPa) and flow rates (65 g/min) were comparable to the ether extractable oil yield (17.88%). Extract yield significantly increased (p0.05) with an increase in pressure and flow rate. However, the temperature effect on extract yield was not significant. Antioxidant extraction significantly increased with increased pressure, but not with increased flow and temperature. These behaviors with pressure, flow and temperature were similar for oryzanol, tocopherols and tocotrienols. Rice hull ash adsorbent did not significantly affect oil yields, but did influence the antioxidants in the extract. A much greater ash adsorption effect for noted for oryzanol, which was different from the effect that was seen for of vitamin E components. A separate batch adsorption study carried out at different temperature (20, 30, 40°C) for varied time intervals also showed similar adsorption behavior. Freundlich isotherms successfully described adsorption behavior of the antioxidant compounds in the batch study using rice bran oil-hexane miscella. Freundlich fitting parameters (k and 1/n) were used to plot Van't Hoff-Arrhenius equations and calculate the change in enthalpy value (DeltaH) due to adsorption of antioxidants. Goto et al. (1993) model was applied to extraction yield data and successfully characterized extraction behavior. Values of partition coefficient K and mass transfer coefficient Kp were calculated and reported.