Antioxidant Activity of Sesamol in Soybean Oil Under Frying Conditions

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 0.02 % (w/w) tert-butylhydroquinone (TBHQ) 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 0.02 % 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 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 0.02 % TBHQ after 8-h frying. This study shows that sesamol can be used as an alternative for synthetic antioxidants for frying oil.