Effect of Pre-Thermal Treatments on Chemical Characteristics, Bioactive Compounds and Microstructure of Rice Bran.

This work was carried out to determine the stability of commercially available rice bran samples subjected to different heat treatments using oven heating, microwave and steaming by autoclave. All rice bran samples were subjected to chemical and microstructure evaluation. Obtained results for chemical constituents indicated that moisture content was varied from 10.54 to 8.65 %. All protein content in stabilized rice bran samples did not exceed 18%, stabilized rice bran in oven  had the highest ash content recording 4.8% in compare with the other samples.  Microstructure analysis performed by scanning electron microscope  SEM revealed that all stabilized rice bran samples have smooth, closed-celled structures. Results of bioactive compounds showed that total phenolic content of stabilized rice bran in oven exhibited the least content of total phenolics being 13.52 mg GAE/100g sample, while total flavonoids content (TFC) gradually decreased in all stabilized rice bran in compare with control. Results of HPLC detected the most abundant phenolic acids in all stabilized rice bran were Ferulic acid followed by Cinnamic acid. Also, gross chemical composition and fatty acid profile of oil extracted from different stabilized rice bran samples were determined. Results of acid value and free fatty acid (FFA%) content of untreated rice bran oil gradually increased from 0.15 to 0.31mg KOH /g and  from 0.3 to 0.6%, respectively, while the changes in oxidation and rancidity parameters were decreased  in all oil samples in compare with control one . also. Oryzanol content  were decreased in all stabilized bran samples. Obtained results showed that total saturated fatty acids were ranged from 28.17 to 32.00 % in all oil samples,  palmitic acid C_16:0 recorded the highest amount of total saturated fatty acids, the epidemic unsaturated fatty acid in all oil samples being oleic acid C_18:0,also  adequate amount of essential fatty acids, linoleic acid C_18:2 ranged from 25.02 to 27.05 %.The minor amounts of  linolenic C_18:3 not exceeded  0.08%  in all rice bran oil sample in compare with 1.35 % in control sample. So, from the above mentioned data it could be concluded that thermal treatments  caused an appreciable changes in total saturated and unsaturated fatty acids. Steaming using autoclave and  irradiation by microwave appeared to be the most effective in stabilizing the rice bran for improving the stability of oil towards oxidation. Microwave  and autoclaving treatment represented a practical tool for rice bran heat stabilization and reaps more advantage of oil compounds considered as a beneficial to human health.