Participation of sesamol in stability of sesame oil

Abstract Sesame oil is known to be the most resistant to oxidative rancidity. Constituents of sesame oil such as sesamolin, sesamol and sesamol dimer (a possible intermediate of oxidative degradation of sesamol) were determined by high performance liquid chromatography using a reverse‐phase column. Sesamol was specifically determined in an alternative way by use of hydrogen peroxide/horseradish peroxidase. Sesamolin was relatively stable but sesamol and sesamol dimer were unstable when irradiated in benzene, and the final degradation products were identical. Whereas sesamolin was inactive, sesamol and sesamol dimer showed significant antioxidant activity in several kinds of fat and oils. Stability of Japan Pharmacopoeia sesame oil free from sesamol was relatively low; antioxidant activity of sesamol incorporated in the oil was unexpectedly low and was rapidly lost in the oil activated by oxygen. Edible sesame oil with intrinsic sesamol was highly stable. Activation of the edible oil gradually increased the sesamol content with concomitant decrease of sesamolin. High stability of edible sesame oil could not be ascribed to sesamol, but it could be explained by another powerful antioxidant(s) which might stabilize both the oil and unstable sesamol.