Degummed rice bran oil was deacidified by caustic, solvent and steam refining processes. The steam refining process was optimized through a series of experiments with varying refining times (1–5 hr), temperatures (220–280 C) and amounts of steam (4–20%), at a pressure of 4 mmHg. The most significant factors affecting the degree of deacidification were the refining temperature and amount of steam. The correlation coefficient between quadratic equation obtained and experimental results was 0.96. Acid value and color of steam refined oil were not as good as those of caustic refined oil, but steam refining showed better retention of natural antioxidants than caustic or solvent refining. Steam refining is preferred for deacidification of rice bran oil because of reduced neutral oil loss and elimination of soap production.The important criteria in selecting a deacidification process are known to be the degree of deacidification, neutral oil loss, effect on bleaching and production of soapstock (2,8–10). In comparing caustic refining, solvent refining and steam refining, caustic refining of degummed rice bran oil resulted in satisfactory acid values and color but showed the worst result in neutral oil loss and produced large amounts of soapstock. Solvent refining was not shown to be efficient because of poor deacidification, high losses of neutral oil and darkening of color. Steam refining also was less effective than caustic refining in deacidification and bleaching. However, the degree of deacidification could be improved by development of a process to remove all the free fatty acids (8), and the color problem could be eliminated by including a preliminary bleaching step before steam distillation (10). The application of steam refining to rice bran oil will result in many advantages such as reduced neutral oil loss, no production of soap, and the production of high purity, industrial fatty acids.
Rice bran oil and double fractionated palm olein (DF palm olein) were heated at 180 C for 50 hr to measure lipid deterioration in the oils. Free fatty acid content of both oils increased during heating; however, iodine value and smoke point decreased. Solid fat contents of both oils were unaffected by heating time. Cloud point of rice bran oil was much lower than that of palm olein. Color of oils changed gradually to dark brown from light yellow with increased heating time. Absolute content of polyunsaturated fatty acid, such as linoleic acid, reduced more than that of monounsaturated fatty acid, such as oleic acid, in both oils. In both oils, iodine value correlated very well with linoleic acid content, with correlation coefficient higher than 0.96.
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