Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2013
Publication Date: 6/7/2013
Citation: Winkler-Moser, J.K., Rennick, K.A., Hwang, H.-S., Berhow, M.A., Vaughn, S.F. 2013. Effect of tocopherols on the anti-polymerization activity of oryzanol and corn steryl ferulates in soybean oil. Journal of the American Oil Chemists' Society. 90:1351-1358.
Interpretive Summary: In this research, we demonstrated that steryl ferulates from corn and rice improved the heat stability of soybean oil. Soybean oil is the most highly produced vegetable oil in the U.S., and is a good source of essential fatty acids as well as Vitamin E (tocopherols). However, because it contains high amounts of polyunsaturated fatty acids, it is easily degraded and polymerized during frying and other high temperature processing conditions. Hydrogenation is used to lower the amount of polyunsaturated fatty acids in soybean oil and therefore, protect it from degradation during frying, but the practice of hydrogenation is not desirable for consumers because it results in the formation of trans fatty acids, which are harmful to health. Therefore, we are researching natural antioxidants to improve the stability of frying oils without hydrogenation. We compared steryl ferulates from corn and rice in their ability to prevent polymerization of soybean oil at frying temperatures, with and without added Vitamin E. Corn steryl ferulates were very effective in preventing polymerization. Rice steryl ferulates were not as effective at preventing polymerization of soybean oil but the antipolymerization activity was improved with added tocopherols, and the tocopherols also protected the corn and rice steryl ferulates. The benefit of using corn and rice steryl ferulates is that they are natural antioxidants that could reduce the use of trans-fat containing hydrogenated soybean oil for frying.
Technical Abstract: Steryl ferulates (SF) are ferulic acid esters of phytosterols and/or triterpene alcohols which have potential as frying oil antioxidants. The objective of this study was to evaluate the anti-polymerization and antioxidant activity at frying temperatures of corn steryl ferulates (CSF), rice steryl ferulates (oryzanol), and a mixture of CSF with oryzanol, alone and with tocopherols. Antioxidant activity was measured by the reduction of polymerized triacylglycerol formation, and loss of olefinic and bisallylic protons from fatty acid double bonds by 1H NMR. CSF and oryzanol slowed the oxidation and polymerization of soybean oil triacylglycerols heated to 180ºC more effectively than a mixture of alpha and gamma tocopherols. CSF were more effective at preventing polymerization than oryzanol, but when oryzanol was combined with tocopherols, they all had similar antioxidant activity. In addition, tocopherols had a protective effect on SF. Corn SF were degraded more quickly during heating than oryzanol, however, the phytosterol constituents of corn SF, sitostanol and campestanol, were actually more resistant to degradation compared to the phytosterol constituents of rice SF. Results demonstrate that corn and rice steryl ferulates may be effective antioxidants for use in frying oils, and that their activity is enhanced in the presence of tocopherols.