Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 6, 2006
Publication Date: December 1, 2006
Citation: Piazza, G.J., Foglia, T.A. 2006. One-Pot Synthesis of Fatty Acid Epoxides from Triacylglycerols Using Enzymes Present in Oat Seeds. Journal of the American Oil Chemists' Society. 83(12):1021-1025. Interpretive Summary: High temperature greases are prepared from special hydroxylated fatty acids obtained from the splitting of castor oil, a material which is imported into the US. It would be desirable to produced high temperature greases from domestic fats and oils. We previously found that an enzyme from oat seeds can catalyze the controlled oxidation of fatty acids, leading to substances that are hydroxylated fatty acid precursors. Much work is needed to purify this enzyme, and we found that ground oat seeds can serve as an expensive source of this enzyme. Further cost reduction could be obtained if whole fats and oils were used as the starting material instead of expensive fatty acids. Using ground oat seeds, we systematically searched for reaction conditions that would activate the "lipase" enzyme found in these seeds because this enzyme will split the fats and oils to their constituent fatty acids. Also we wanted to use the oxidation enzyme in oats discussed above to produce the hydroxylated fatty acid precursor. We found that when a special surfactant is added to ground oat seeds and specific reaction conditions are used, whole fats and oils are partially converted to fatty acids that are sequentially converted to hydroxylated fatty acid precursors useful for the preparation of high temperature greases.
Technical Abstract: In our previous work we used ground oat (Avena sativa) seeds as an inexpensive source of enzymes for the modification of fats and oils and/or their chemical derivatives. We have extended this work by observing the products derived from an intact fat and three vegetable oils through the concerted action of oat seed lipase and peroxygenase. A modified reverse phase HPLC protocol was devised that allowed the quantitation of free fatty acids, epoxy fatty acids, and acylglycerols without derivatization. It was found that the addition of the surfactant deoxycholate or calcium chloride was needed to observe best conversions to fatty acids. Without an added oxidant, lipase action produced up to 80% by weight of fatty acids at pH 7-9 with small amounts of diacyglycerols and monoacylglycerols. When the oxidant t-butyl hydroperoxide was added in the presence of deoxycholate, the fatty acids were partially converted to epoxide derivatives (up to 35% by weight) by the peroxygenase present in the oat seeds. When calcium chloride replaced deoxycholate only 4% by weight of the product was epoxide derivatives. The highest levels of fatty acid epoxides were produced at pH 7, but epoxidized acylglycerols were not detected. However, at pH 7 up to 15% by weight of the product was hydroxystearic monoglyceride. The optimal molar amount of t-butyl hydroperoxide to add with deoxycholate for high epoxide formation was found to be 1.4 to 2.8 times the amount of fatty esters in soybean oil. The fatty epoxide products may be used to produce polyols with high viscosity for grease preparations.