Investigating the Effect of Heat Treatment on the Compounds and Antimicrobial Properties of Shirazi Thyme and Cinnamon Essential Oils

Nowadays if essential oils can remain stable in food processing conditions, they can be used as an alternative to synthetic preservatives in food products. In this research, in addition to investigating the compounds of Zataria multiflora and cinnamon essential oils by gas chromatography-mass spectrometry, the antimicrobial properties of two essential oils before and after heat treatment (200 °C; 10 min) against Bacillus subtilis and Aspergillus niger were evaluated. Based on the obtained results, the thermal process did not significantly affect the main compounds of the essential oils. Cinnamaldehyde and eugenol were the main constituents of cinnamon essential oil, while phenolic compounds (thymol and carvacrol) made up 61.5% of Z. multiflora essential oil. The minimum inhibitory concentrations (MICs) of Z. multiflora and cinnamon essential oils against Aspergillus niger were 250 and 4000 µL/mL, respectively, while the minimum fungicidal concentrations (MFCs) were 250 and 16,000 µL/mL, respectively. Against Bucillus subtilis, the MIC and minimum bactericidal concentrations (MBC) values were 7.8 and 15.6 µL/mL for Z. multiflora, and 16,000 and 32,000 µL/mL for cinnamon, respectively. The inhibition zones of heated Z. multiflora and cinnamon essential oils were 20.5 and 16.05 mm against A. niger and 29.00 and 17.00 mm against B. subtilis, respectively. In general, the results demonstrated that the thermal process did not significantly affect the antimicrobial activity of the essential oils, meaning that they are suitable for use as antimicrobial agents in products that undergo thermal processing.