Rice bran oil. IV. Storage of the bran as it affects hydrolysis of the oil

Summary and Conclusions The oil, contained in bran from regularly milled rice, when stored at prevailing atmospheric temperature, humidity, and natural moisture content is subject to rapid hydrolysis which increases the free fatty acid content of the oil to a point where it cannot be economically refined. Data have been presented showing the effects of a) temperature, b) drying at temperatures of 70°, 85°, 100°, and 110°C. for various periods of time up to 5 hours, c) different relative humidities before and after drying, and d) added moisture on the rate of formation of free fatty acids during storage in bran from both regular and “Converted” rice. Decreasing the storage temperature tends to retard the formation of free fatty acids. In the case of regular rice bran deterioration during storage occurred at a fairly rapid rate even at 3°C. whereas bran from “Converted” rice was fairly stable when stored at this temperature. The investigation of the effect of heating or drying and the effect of different relative humidities on the storage of rice bran have shown that bran from both regular and “Converted” rice can be stored for periods of at least four months without excessive increase in the content of free fatty acids, provided the bran is dried sufficiently and is maintained at a low moisture content. An increase in the moisture content of predried bran causes a rapid increase in the free fatty acid content of the oil in the bran. Investigations of the effect of chemical inhibitors and of inert atmosphere on the rate of free fatty acid formation of regular rice bran indicated that these were ineffective in preventing deterioration. Presented at the 40th Annual Meeting of the American Oil Chemists’ Society, New Orleans, La., May 10–12, 1949; Report of a Study Made Under the Research and Marketing Act of 1946. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.