Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2013
Publication Date: 1/30/2013
Citation: Hwang, H.-S., Winkler-Moser, J.K., Bakota, E.L., Berhow, M.A., Liu, S.X. 2013. Antioxidant activity of sesamol in soybean oil under frying conditions. Journal of the American Oil Chemists' Society. 90:659-666.
Interpretive Summary: In this research, we found that a natural antioxidant, sesamol, at certain concentrations could show a better antioxidant activity than a synthetic antioxidant at 200 ppm concentration for frying oil. We also improved the addition method of sesamol so that we could achieve a significantly reduced oxidation for soybean oil during frying. Soybean oil has high contents of polyunsaturated fatty acids, which are good for health. However, soybean oil is not widely used in the food industry for frying oil due to the high reactivity to oxidation of polyunsaturated fatty acids in it. Because of that, a strong antioxidant is needed for utilization of soybean oil as frying oil. Synthetic antioxidants are strong antioxidants, but their quantity is limited by law to 200 ppm due to the potential toxicity. This relatively small quantity cannot provide sufficient oxidative stability for soybean oil at frying condition. Therefore, non-toxic natural antioxidants with strong antioxidant activity are needed, which can be used at a higher concentration than 200 ppm for better protection of frying oil from oxidation. We tested a promising natural antioxidant, sesamol, in the miniaturized frying experiment and found that certain concentrations of sesamol could give a better antioxidant activity than the legally limited amount of synthetic antioxidant. We found that evaporation and decomposition of sesamol during frying are serious problems, which significantly reduce the effectiveness of sesamol. To solve this problem, we developed the multiple addition method, which resulted in much more improved antioxidant activity than one single addition of the same amount of sesamol. This research revealed not only that sesamol can replace synthetic antioxidants, but also that the healthy soybean oil can be used in the food industry as frying oil when sesamol is added by the multiple addition method. This research would expedite the practical application of natural antioxidants and utilization of soybean oil as frying oil in the food industry.
Technical Abstract: Antioxidant activity of sesamol was investigated in soybean oil using a miniaturized frying experiment with potato cubes fried at 180 °C. Oxidation of soybean oil was determined by gel permeation chromatography for polymerized triacylglycerols and by 1H NMR spectroscopy for reactions at reactive sites of soybean oil molecules including olefinic, bisallylic and allylic protons during frying. Sesamol showed lower antioxidant activity than 0.020% (w/w) TBHQ (tert-butylhydroquinone) at the same molar concentration. Higher concentrations of sesamol provided better antioxidant effects indicating that no prooxidant activity occurred. Sesamol in this frying test showed better results than 0.020% TBHQ when the concentration was as high as 0.66% by weight. An HPLC experiment showed that the concentration of sesamol decreased sharply during frying. Thermogravimetric analysis (TGA) indicated that sesamol is highly volatile and easily oxidizes when exposed to air. To overcome this problem, two multiple addition methods were evaluated in which sesamol was added portion by portion every hour. The multiple additions of divided portions of 0.66% (w/w) sesamol maintained the concentration of sesamol at the minimum of 0.04-0.06% throughout the frying process and showed improved antioxidant activity compared to one single addition of 0.66% sesamol at the beginning of frying. One of the multiple addition methods showed 28, 18, 59, and 27% less polymerized triacylglycerols and losses of olefinic, bisallylic and allylic protons, respectively, than 0.020% TBHQ after 8-hr frying. This study shows that sesamol can be used as an alternative for synthetic antioxidants for frying oil.