Mahboobe Gaeini - Department of Food Science and Technology, College of Agriculture, Islamic Azad University Varamin, Iran.
Rezvan Pourahmad - Department of Food Science and Technology, College of Agriculture, Islamic Azad University Varamin, Iran.
Mohammad Reza Haeri - Department of Clinical Biochemistry, Faculty of Medicine, Qom University of Medical Sciences, Qom, Iran.

Introduction: Diseases caused by the consumption of bacteria-contaminated foods have been of great importance in public health. Therefore, control of dairy product contamination with coliforms is a concern for the durability of dairy producers. Control of the contamination by natural products may have dual action; nutritive value and natural antibiotics. In this study, the antimicrobial activity of thyme essential oil against Escherichia coli O۱۵۷: H۷ in doogh (Iranian fermented dairy drink) was examined and the MIC and MBC were determined. Methods: Antimicrobial activity of thyme essential oil was examined using different concentrations (۰, ۳۰, ۶۰, ۹۰, and ۱۲۰ μl/ml) against bacteria with a density of ۱۰۵CFU/ml during the ۶۰-day at ۴ °C. Moreover, the effect of different concentrations of essential oils on the taste of doogh was also studied. Taste evaluation was performed based on ۵ points hedonic test to evaluate the effect of Thyme oil on the sense of taste. Duncan software was used to determine the difference between test and control groups at a confidence level of ۵%. The SPSS software was also used for statistical analysis. Results: All concentrations of thyme essential oil could stop the growth of bacteria (P<۰.۰۵). The inhibitory effect of oil increased with increasing concentration and time. Based on the results of sensory (taste) evaluation, treatment ۲ (containing ۶۰ μl/ml of essential oil of thyme) was selected as the best treatment. Conclusion: Thyme essential oil can be used as a natural preservative with a positive impact on taste and nutritive value.

Doogh, Thyme, Escherichia coli, Minimum bactericidal concentration