Materials and Methods: In this study, the effect of essential oils of rosemary, pennyroyal, thyme, mint, peppermint, mastic gum, and frankincense as natural antioxidants in concentrations of 250, 500, 750, and 1000 ppm in comparison with tert-butyl-hydroquinone (TBHQ) (100 ppm) on the quality characteristics of black seed oil and its thymoquinone content during 90 days of storage was studied.

Results: The results showed that the incorporation of essential oils was more effective than TBHQ in increasing oxidative stability and reducing peroxide and acid values. Among essential oils, rosemary was more effective in increasing the oxidation stability index. Rosemary (750 ppm) and mastic gum (500 ppm) were more effective in controlling the peroxide value. The addition of essential oils to black seed oil did not result in a significant alteration (P > 0.05) in the thymoquinone content. However, it did inhibit the decomposition and loss of this compound.

Conclusions: It was concluded that essential oils could be a good alternative to TBHQ for increasing the black seed oil stability, shelf life and preservation. Given the numerous pharmaceutical applications of black seed oil, the findings of this study can be utilized to improve the stability of black seed oil and formulations containing it, as well as to enhance the stability of thymoquinone, which holds therapeutic potential, during storage.