Introduction: Recently, atmospheric pressure non-thermal plasma has been used as a new method for decontamination of medicinal plants. The aim of this research was to investigate the effects of atmospheric pressure floating-electrode dielectric-barrier discharge (FE-DBD) on Nigella sativa (N. sativa) which has many therapeutic properties.
Materials and methods: N. sativa seeds were exposed to atmospheric pressure FE-DBD plasma for 15, 30 and 40 min. and total microbial counting of the seeds was performed. Antioxidant activity and total phenol were measured to evaluate the chemical properties changes of N. sativa seeds under the exposure of plasma. Fatty acid analysis of the extracted oil from N. sativa was determined using gas-liquid chromatography in this research before and after the exposure to cold plasma.
Results: The results showed that the density of microorganisms significantly decreased at all three exposure times compared to the control (P˂0.05) and eliminate total microorganisms at 40 min of exposure. There was no significant change in the amount of total phenolic compounds and antioxidant activity before and after plasma exposure. Linoleic acid and oleic acid were decreased under the exposure of FE-DBD plasma for 40 min which indicate that cold plasma can lead to the oxidation of unsaturated fatty acids. The ratio of unsaturated fatty acids to saturated fatty acids were significantly decreased (P˂0.05).   
Conclusion: In conclusion, exposure of cumin seeds to FE-DBD plasma can effectively reduce or eliminate microorganisms. On the other hand, cold plasma treatment brings about some biochemical changes. Total phenol content increased and antioxidant activity was decreased slightly. The unsaturated fatty acid contents of black cumin seeds samples decreased with FE-DBD plasma exposure at effective time for decontamination.