Effects of free fatty acids and peroxide on thermal loss of sesamol and formation of its transformation products in soybean oil
Jingnan Chen, Wang Ya, Wei Liu, Zhang FeiHong, Jun Li, Huifang Yang, Yanlan Bi
Abstract
Sesamol, as a natural antioxidant used in edible oils, will be lost during heating process in the pathway of volatilization or transformation. The present study was to (i) examine the effects of temperatures, acid value (AV), free fatty acids (FFAs), and peroxide value (POV) on the thermal loss of sesamol in soybean oil (SBO); (ii) to investigate the corresponding transformation mechanism of sesamol; and (iii) to investigate the antioxidant ability and mechanism of the transformation products. Temperatures, FFAs and elevation of AV and POV of SBO significantly accelerated sesamol loss. Volatilization was the main mechanism for the thermal loss of sesamol, while a small portion of sesamol was transformed. The HPLC-MS and NMR analysis found that the main transformation product was a sesamol dimer. The underlying mechanism was that sesamol reacted with lipid radicals (R·) or lipid peroxide radicals (ROO·) to produce phenoxy radicals in soybean oil and then two of these stable resonant phenoxy radicals combined to form a dimer of sesamol. Moreover, the sesamol dimer showed better antioxidant ability than sesamol in SBO due to the higher activity of hydrogen protons on phenolic hydroxyl groups and the sturdy coplane structure of resonant intermediates.