IMPROVING STABILITY AND HEALTHFULNESS OF U.S. COMMODITY VEGETABLE OILS AND PRODUCTS
Location: Functional Foods Research Unit
Title: Comparison of the impact of y-oryzanol and corn steryl ferulates on the polymerization of soybean oil during frying
Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 29, 2011
Publication Date: July 21, 2011
Citation: Winkler-Moser, J.K., Rennick, K.A., Palmquist, D.E., Berhow, M.A., Vaughn, S.F. 2011. Comparison of the impact of y-oryzanol and corn steryl ferulates on the polymerization of soybean oil during frying. Journal of the American Oil Chemists' Society. 89:243-252.
Interpretive Summary: In this research, we demonstrated that corn steryl ferulates improved the stability of soybean oil used for frying. 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. However, because it contains high amounts of polyunsaturated fatty acids, it is easily degraded and polymerized during frying. 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 favorable 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 during frying. Corn steryl ferulates were very effective in preventing polymerization, and they also protected the tocopherols (Vitamin E) that were naturally present in the soybean oil. Rice steryl ferulates were not as effective at preventing polymerization of soybean oil, and increased the degradation of tocopherols. From these results it appears that corn steryl ferulates may be effective at improving the stability of soybean oil, so that it can be used for frying instead of hydrogenated soybean oil.
Corn steryl ferulates (CSF), oryzanol, a combination of equal amounts of CSF and oryzanol, and ferulic acid were added to refined, bleached, deodorized, soybean oil at a concentration of 8.1-8.4 µmol/g oil, which corresponded to 0.5% (w/w) for the steryl ferulates. The rate of polymerized triacylglycerol (PTAG) formation was determined in three replicate two-day frying experiments using a miniature frying protocol with potato cubes. Oryzanol and ferulic acid slightly inhibited PTAG formation on the first day of frying. However, the two treatments were not significantly different from the SBO control on the second day of frying. CSF and the combination of CSF and oryzanol significantly inhibited PTAG formation on both days of frying, but the combination was slightly more effective on the second day of frying. Tocopherol degradation in SBO with added oryzanol or ferulic acid proceeded more rapidly compared to the control. However, CSF and the combination of CSF and oryzanol appeared to protect tocopherols from degradation. In addition, CSF was more stable to frying compared to oryzanol, but when CSF and oryzanol were combined, CSF protected oryzanol from degradation.