Alteration in Thymoquinone Content of Nigella sativa Seeds After Processing by a Traditional Method and Stability Assessment of Raw and Processed Seeds

Background and objectives: Nigella sativa L. is one of the most important species in Iranian traditional medicine (ITM). According to ITM, the plant seeds can cause bronchospasm in patients with hot temperament; therefore it is recommended to process the seeds with grape vinegar before usage. This process may influence some components of the seeds; thus, in the present investigation, the effect of processing on thymoquinone, which is one of the most important active ingredients of the seeds, has been studied. Moreover, the stability of Nigella capsules containing raw and processed seeds and Nigella-honey mixture, “Maajoon”, were assessed. Methods: Nigella sativa seeds were processed by two methods: vinegar was added to the whole intact seeds, then the seeds were dried and crushed; the second method consisted of first crushing the seeds and then performing the vinegar adding and drying steps. The essential oil of the powders was obtained by using hydrodistillation method and thymoquinone content of the oils was measured by gas chromatography. In order to estimate the stability of the Nigella capsules and “Maajoon”, thymoquinone content of the products was measured after one, two and three months at room temperature. Results: The results showed that thymoquinone was absent in the processed seeds which were powdered before processing; but thymoquinone percentage had decreased in processed seeds which were powdered after processing (maximum content: 64.1%). The reduction of thymoquinone after three months was 40.1 and 78.5% in raw and processed capsules, respectively. No thymoqinone was found in the “Maajoon”. Conclusion: Since many effects of Nigella is due to thymoquinone, it seems that grinding before processing and making “Maajoon” are not suitable methods for Nigella preparation. Powdering after processing had decreased thymoquinone content which might result in decrease in bronchospasm as the side effect of thymoquinone; therefore, this method of processing seems to be suitable.  Due to low stability of Nigella powder, powdering just before usage is recommended when necessary.