Effect of thymoquinone and tocopherols on the oxidative stability of purified Nigella sativa oil

Abstract

The effect of minor bioactive constituents (alpha-, gamma-tocopherol and thymoquinone) and the binary and ternary mixtures of those constituents on the oxidative stability of purified black cumin oil (PBCO) was evaluated. PBCO [purified triacylglycerols (TAG)] was enriched with different concentrations of these bioactive compounds then subjected to an accelerated thermal oxidation tests in a Rancimat apparatus at 90 degrees C and in an oven at 60 degrees C. The induction period (IP) of purified TAG containing ternary mixtures of minor bioactive constituents was higher than that of control purified TAG. Peroxide value (PV), conjugated diene (K232), panisidine value ov) and polymer triglyceride content were measured dur ing storage at 60 degrees C. A ternary mixture of minor bioactive constituents was more effective to retard oil oxidation than a binary mixture. In addition, purified TAG containing individual and binary mixture with gamma-tocopherol were more stable towards oxidation. During storage at 60 degrees C, alpha-tocopherol disappeared rapidly followed by gamma-tocopherol. The more resistant minor compound towards oxidation was thymoquinone wherein a slight decrease in its amount was observed at the end of storage experiment.