Submitted to: European Journal of Lipid Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/12/2007
Publication Date: 5/1/2008
Citation: Winkler, J.K., Warner, K.A. 2008. The effect of phytosterol concentration on oxidative stability and thermal polymerization of heated oils. European Journal of Lipid Science and Technology. 110:455-464. Interpretive Summary: There is a lot of interest in finding natural alternatives to synthetic antioxidants to help increase the stability of vegetable oils during frying and other high-heat applications. Phytosterols are naturally abundant in vegetable oils, but little is known about their impact on vegetable oil stability. In this study we looked at the effect of added phytosterols on vegetable oil stability at frying temperature. It was and found that when higher amounts of phytosterols were added to soybean oil, they increased the soybean oil stability. However, this impact was not found when phytosterols were added to a high-stability sunflower oil, and at very high concentrations the phytosterols actually decreased the stability of this sunflower oil. This research indicates that phytosterol concentration can impact stability of vegetable oils during heating, depending on the type of vegetable oil is being used.
Technical Abstract: This study determined the effect of adding mixed phytosterols, at various concentrations, on the thermal polymerization and oxidative stability index (OSI) of soybean and high-oleic sunflower oils. The indigenous tocopherols and phytosterols were removed from the oils by molecular distillation. Pure phytosterols were added back to these stripped oils at concentrations of 0.25, 0.5, 1, and 2.5 wt%. These oils were heated at 180 deg C, and triacylglycerol dimers and polymers, fatty acid composition, and residual phytosterols were determined. Added phytosterols at 1 and 2.5% significantly decreased thermal polymerization of stripped soybean oil over 8 hr. Phytosterols at 2.5% significantly increased polymerization of stripped high-oleic sunflower oil over 12 hr. Added phytosterols did not affect the loss of polyunsaturated fatty acids in either oil. The decomposition of the added phytosterols was followed in both oils during the heating study. Phytosterols loss in soybean oil ranged from 7-13%, while loss in stripped high-oleic sunflower oil ranged from 13-20%. Phytosterols added at 1 and 2.5% significantly decreased the OSI for stripped high-oleic sunflower oil.