Highly Efficient Deacidification of High-Acid Rice Bran Oil Using Methanol as a Novel Acyl Acceptor
A highly efficient process for reducing the fatty acid (FA) content of high-acid rice bran oil (RBO) was developed by immobilized partial glycerides-selective lipase SMG1-F278N-catalyzed esterification/transesterification using methanol as a novel acyl acceptor. Molecular docking simulation indicated that methanol was much closer to the catalytic serine (Ser-171) compared with ethanol and glycerol, which might be one of the reasons for its high efficiency in the deacidification of high-acid RBO. Additionally, the reaction parameters were optimized to minimize the FA content of high-acid RBO. Under the optimal conditions (substrate molar ratio of methanol to FAs of 1.8:1, enzyme loading of 40 U/g, and at 30 °C), FA content decreased from 25.14 to 0.03% after 6 h of reaction. Immobilized SMG1-F278N exhibited excellent methanol tolerance and retained almost 100% of its initial activity after being used for ten batches. After purification by molecular distillation, the final product contained 97.86% triacylglycerol, 2.10% diacylglycerol, and 0.04% FA. The acid value of the final product was 0.09 mg KOH/g, which reached the grade one standard of edible oil. Overall, methanol was a superior acyl acceptor for the deacidification of high-acid RBO and the high reusability of immobilized SMG1-F278N indicates an economically attractive process.
KeywordsDeacidification High-acid rice bran oil Methanol Molecular docking Partial glycerides-selective lipase
This work was supported by the National Natural Science Foundation of China (21376098) and the Science and Technology Planning Project of Guangdong Province (2014B020204003, 2015B020231006, 2015TX01N207).
Compliance with Ethical Standards
Conflict of Interest
The authors declare that they have no conflict of interest.
- 4.Wilson, T. A., Nicolosi, R. J., Woolfery, B., & Kritchevsky, D. (2007). Rice bran oil and oryzanol reduce plasma lipid and lipoprotein cholesterol concentrations and aortic cholesterol ester accumulation to a greater extent than ferulic acid in hypercholesterolemic hamsters. The Journal of Nutritional Biochemistry, 18, 105–112.CrossRefGoogle Scholar
- 5.Chou, T. W., Ma, C. Y., Cheng, H. H., Chen, Y. Y., & Lai, M. H. (2009). A rice bran oil diet improves lipid abnormalities and suppress hyperinsulinemic responses in rats with streptozotocin/nicotinamide-induced type 2 diabetes. Journal of Clinical Biochemistry and Nutrition, 45, 29–36.CrossRefGoogle Scholar
- 17.Zheng, M. M., Zhu, J. X., Huang, F. H., Xiang, X., Shi, J., Deng, Q. C., Ma, F. L., & Feng, Y. Q. (2015). Enzymatic deacidification of the rice bran oil and simultaneous preparation of phytosterol esters-enriched functional oil catalyzed by immobilized lipase arrays. RSC Advances, 5, 70073–70079.CrossRefGoogle Scholar
- 18.Xu, T. T., Liu, L., Hou, S. L., Xu, J. X., Yang, B., Wang, Y. H., & Liu, J. S. (2012). Crystal structure of a mono- and diacylglycerol lipase from Malassezia globosa reveals a novel lid conformation and insights into the substrate specificity. Journal of Structural Biology, 178, 363–369.CrossRefGoogle Scholar
- 22.Trott, O., & Olson, A. J. (2010). AutoDock Vina: improving the speed and accuracy of docking with a new scoring function, efficient optimization, and multithreading. Journal of Computational Chemistry, 31, 455–461.Google Scholar