Structural Effect of Lignans and Sesamol on Polymerization of Soybean Oil at Frying Temperature

Abstract

AbstractThe antipolymerization activity of the lignans including nordihydroguaiaretic acid, (+)‐pinoresinol, (−)‐secoisolariciresinol, enterodiol, and two sesame lignans (sesamol and sesamin), and four model compounds (4‐ethylcatechol, 2‐methoxy‐4‐propylphenol, 4‐methyl‐2,6‐dimethoxyphenol, and piperonyl alcohol) were investigated for soybean oil at frying temperature (180 °C). The heated samples were analyzed by gel‐permeation chromatography for polymerized triacylglycerols and by 1H NMR to monitor the decrease in peak intensities for bisallylic protons and olefinic protons. The heating test results were compared with ability to scavenge the radical 2,2′‐azinobis‐(3‐ethylbenzothiazoline‐6‐sulfonic acid) 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 solely from the radical‐scavenging ability at room temperature. The lignans tested in this research had antipolymerization activity, but it was not as strong as that of 200 ppm tert‐butylhydroquinone (TBHQ) with equivalent of phenolic moiety (0.0012 meq/g). At higher concentrations, however, sesamol, nordihydroguaiaretic acid, and (+)‐pinoresinol had better antipolymerization activity than the legal limit set for TBHQ (200 ppm, 0.0012 meq/g). Therefore, this research showed that by using an appropriate concentration, these natural antioxidants can replace synthetic antioxidants and provide better antioxidation activity.