Changes of Antioxidants and Fatty Acid Composition in Stabilized Rice Bran During Storage.

The effects of extrusion temperature and post extrusion holding time, microwave heating, and gamma irradiation on antioxidants and lipid composition in rice bran were studied. Post extrusion holding time had no apparent effect on rice bran stability. Increased holding times reduced (p $\u3c$ 0.05) total vitamin E. Oryzanol concentration was lower (p $\u3c$ 0.05) only with 6 min holding time. Inactivation of lipolytic enzymes was obtained by extrusion temperatures of 120, 130, and 140$\sp\circ$C. Increased extrusion temperatures reduced the retention of vitamin E and oryzanol during storage. An extrusion temperature of 110$\sp\circ$C provided the highest retention of vitamin E and oryzanol during storage although FFA level was higher (p $\u3c$ 0.05) than that of the other extrusion temperatures from 105 to 375 days. There were no significant (p $\u3e$ 0.05) decreases in individual vitamin E vitamers until 4 min microwave heating. After 8 min heating, individual E vitamers decreased significantly (p $$ 0.05) in FFA level by 24 weeks of storage with microwave heating for 12 min. Microwave heating for 4, 8, and 12 min did not provided adequate inactivation of lipolytic enzymes. Total vitamin E loss was between 7 and 37% during microwave heating and a further 75-80% reduction occurred during storage. FFA level in rice bran irradiated at 5 kGy was not significantly different from raw rice bran. Increases in irradiation dose of 10 and 15 kGy resulted in an increase in FFA levels. Gamma irradiation in rice bran did not inactivate lipolytic enzymes in the range used in this study. Gamma irradiation did have deleterious effect on lipid stability in rice bran during irradiation and storage. The decomposition of individual E vitamers increased with increased irradiation level. Decomposition of oryzanol increased (p $\u3c$ 0.05) with an increase from 5 to 10 kGy. The loss of total E vitamers and oryzanol occurred in two stages: 50-82% and 12-33% immediately following irradiation, and a further 10-35 and 39-42% during storage