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Title: HYDROLYTIC DEGRADATION OF TRIACYLGLYCERLS AND CHANGES IN FATTY ACID COMPOSITION IN RICE BRAN DURING STORAGE

Author
item Goffman, Fernando
item Bergman, Christine

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2003
Publication Date: 7/1/2003
Citation: GOFFMAN, F.D., BERGMAN, C.J. HYDROLYTIC DEGRADATION OF TRIACYLGLYCERLS AND CHANGES IN FATTY ACID COMPOSITION IN RICE BRAN DURING STORAGE. CEREAL CHEMISTRY. 2003. p. 446-449

Interpretive Summary: The rapid enzymatic decomposition of rice bran lipids after milling is a serious problem which limits its use. We have followed both the degradation and the quality changes of rice bran lipids in a conventional U.S. long grain('Cypress') and a conventional U.S. medium grain ('Earl') cultivar. The lipids of Cypress were degraded faster compared to those of Earl, this was related to the higher oil content and lipase activity of Cypress. The results indicate that lipid content and enzymatic activity are both important factors affecting the rate of lipid degradation in rice bran. These findings indicate that it is possible to create rice cultivars with bran that has a diminished susceptibility to becoming rancid.

Technical Abstract: Rapid degradation of lipids after milling makes rice bran unsuitable for human consumption. To better understand these lipolytic processes, bran from a conventional U.S. long ('Cypress') and medium grain ('Earl') rice cultivar were stored at room temperature for six months, and the changes in triacylglycerol content, fatty acid composition and free fatty acids (FFAs) were followed. Cypress showed a faster rate of triacylglycerol degradation compared to Earl, which apparently was due to its higher lipase activity (ca. 26% higher, P<0.001). The palmitic acid percentage was similarly reduced in both cultivars to about 80% of its initial concentration. Oleic and linoleic acids remained unchanged. The final content of FFAs was ca. 58% higher in Cypress than in Earl (P<0.001). The difference appeared to result from both the higher initial triacylglycerol content (23.5 and 18.3 mg triacylglycerol per 100 mg bran in Cypress and Earl, respectively) and lipase activity of Cypress. The results suggest a means of reducing rice bran rancidity by selecting breeding lines with lower bran oil content and lipase activity.