Background and purpose: Today, the use of natural preservatives in increasing meat products shelf life has gained much attention. In this study, we aimed at evaluating the effects of eucalyptus and cuminum essential oils on microbial quality of Oncorhynchus mykiss.

Materials and methods: In an experimental study the eucalyptus and cuminum essential oils were prepared and their antibacterial activities were evaluated against Shigella dysenteriae, Listeria monocytogenes, Streptococcus pyogenes, and Salmonella typhi by micro dilution method. Then, the effects of eucalyptus and cuminum essential oils were examined on microbial quality of Oncorhynchus mykiss at 8±1 °C in zero, 3 and 6 days in different forms and concentrations (alone: eucalyptus 0.25% and cuminum 0.5%, combined: 0.5% + 0.5%, and also incorporated with chitosan: 0.25% and 0.5%). Data analysis was performed in SPSS ver.16 applying ANOVA and Duncan test.

Results: The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for the essential oils ranged between 0.351 and 11.25, and 1.406 and 11.25 mg/ml, respectively. Eucalyptus essential oil at 0.5% concentration was found to have the best effect on decreasing the total count of bacteria, enterobacteriaceae and psychrotrophic bacteria in fish. Also, combination of chitosan and the essential oils decreased the total count of bacteria, enterobacteriaceae and psychrotrophic bacteria (P<0.05). The antibacterial effects of essential oils (alone) were lower compared to synergistic antibacterial activities of essential oils with chitosan (P<0.05).

Conclusion: Eucalyptus and cuminum essential oils could be used as alternative for chemical preservatives and also in active packaging in meat industry.