The present study aimed to evaluate the in-vitro antioxidant and antimicrobial activity of Thymoquinone (TQ), Eugenol (EUG) and their synergistic effects in combination.

Materials:

 The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), fractional inhibitory concentration (FIC), and disc diffusion tests were used to determine the antibacterial activity of TQ and EUG.  Moreover, Reducing Power Assay and DPPH (2.2-diphenyl-2-picrylhydrazyl) tests were used to indicate the antioxidant ability of TQ and EUG.  The combination index (CI) of these compounds was calculated to evaluate their interaction type.

Bacillus cereus, Listeria monocytogenes, and Shewanella SP were the most sensitive bacteria than other studied pathogens to TQ and EUG, with MIC 0.019, 0.07, and 0.07 mg/ml for TQ and 0.6, 0.6, and 0.6 mg/ml for EUG, respectively.  The mixture of two ingredients showed a good antimicrobial and synergistic effects against all tested bacteria. The DPPH scavenging activity of the combination of TQ+ EUG were antagonistic in all combined concentrations except for TQ (5 mg/ml) + EUG (1.25 mg/ml) and TQ (2.5 mg/ml) + EUG (0.3 mg/ml) treatments.

The obtained results provided a new combination of antimicrobial and antioxidant agents in drug delivery, especially in food preservation systems, to enhance food shelf life in the food industry.