Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2011
Publication Date: 1/12/2012
Citation: Hwang, H., Winkler-Moser, J.K., Liu, S.X. 2012. Structural effect of lignans and sesamol on polymerization of soybean oil at frying temperature. Journal of the American Oil Chemists' Society. 89:1067-1076.
Interpretive Summary: Research was conducted to find out the antioxidant activity of lignans, natural antioxidants for soybean oil at the frying temperature. Even though vegetable oils such as soybean oil are known to have nutritional benefits due to polyunsaturated fatty acids in them, oxidation of these oils limits their utilization in food industry as frying oil. Synthetic antioxidants are being currently used in many foods, but they are known to be toxic and the quantity allowed in food is limited. The limited quantity is not good enough to prevent oxidation of frying oil and the current major solution is to use oils with trans fat and saturated fat, which are not good for health. This research found that three lignans showed better antioxidation activity than a synthetic antioxidant when they are used in higher concentrations. Among them, sesamol showed the best results. Sesamol is relatively inexpensive and shows many health benefits. The importance of this research for the food industry is that sesamol and other lignans can replace synthetic antioxidants. This provides not only higher antioxidation activity but also other health benefits.
Technical Abstract: Antipolymerization activities of lignans including nordihydroguaiaretic acid, (+)-pinoresinol, (-)-secoisolariciresinol, enterodiol, two sesame lignans (sesamol, sesamin), and four model compounds were investigated for soybean oil at frying temperature (180 °C). The heated samples were analyzed by GPC (gel permeation chromatography) for polymerized triacylglycerols and 1H NMR for monitoring decrease in peak intensities of bisallylic protons and olefinic protons. The heating test results were compared with the radical scavenging abilities toward ABTS (2,2’-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)) radical to understand the relationship between radical scavenging ability at room temperature and antipolymerization activity at 180 °C. It was found that the antipolymerization activity of a lignan at frying temperature cannot be predicted by only the radical scavenging ability at room temperature. Lignans tested in this research showed antipolymerization activities, but not as strong as 200 ppm TBHQ (tert-butylhydroquinone) with the same equivalent of phenolic moiety (0.0012 meq/g). At higher concentrations, however, sesamol, nordihydroguaiaretic acid and (+)-pinoresinol showed better antipolymerization activity than the legally limited amount of TBHQ (200 ppm, 0.0012 meq/g). Therefore, this research showed that a proper concentration of a lignan, the non-toxic natural antioxidant can replace synthetic antioxidants providing not only better antioxidation activity but also health benefits.