en تخصصي Special Original article Original article <p style="text-align: justify;"><span style="font-family:times new roman;"><strong>Background: </strong>Yogurt is one of the most popular food diets with refreshing taste, nutritional, and health benefits. The objective of this study was to investigate the effect of three herbal Essential Oils (EOs) including peppermint, basil, and zataria on viability of the probiotic bacteria in yogurt samples and to evaluate the antimicrobial activities of the produced probiotic yogurts against <em>Escherichia coli</em> and <em>Listeria monocytogenes</em>.<br> <strong>Methods:</strong> Yogurt samples were produced using probiotic organisms <em>Lactobacillus acidophilus</em> LA5, <em>L. fermentum</em>, and <em>Bifidobacterium</em> Bb-12 besides the starter culture and added EOs, separately. The value of pH, viable counts of probiotics, and antimicrobial potential of yogurts at 0, 7, 14, and 28 days of storage at 4 ^&deg;C were evaluated. The growth inhibition of <em>E. coli</em> and <em>L. monocytogenes</em> was determined <em>in vitro</em> using disk diffusion method. All data analyses were performed using SPSS, Inc, Chicago, IL software (v. 16.0).<br> <strong>Results:</strong> No significant difference was observed in pH value of treatment (EOs containing probiotic yogurts) and control samples during fermentation and storage period. The presence of EOs did not affect the total lactobacilli and <em>L. acidophilus</em> LA5 population in yogurt during 4 weeks of storage but the growth of <em>Bifidobacterium</em> Bb12 was retarded. Yogurt containing zataria exhibited the strongest inhibitory effect on the growth of <em>E. coli</em> and <em>L. monocytogenes</em> in comparison with other EOs treated and control yogurt (<em>p</em><0.05). However, both control as well as treated yogurt showed inhibitory effect against<em> L. monocytogenes</em> stronger than <em>E. coli </em>(<em>p</em><0.05).<br> <strong>Conclusion:</strong> The present findings suggested that adding zataria, basil, or peppermint EOs into probiotic yogurt formulation could improve the potential functionality of the product and also made an inhibitory effect against<em> L. monocytogenes</em> and <em>E. coli.</em></span></p> Anti-Bacterial Agents, Oils Volatile, Probiotics, Yogurt 79 86 http://jfqhc.ssu.ac.ir/browse.php?a_code=A-10-1-122&slc_lang=en&sid=1 M. Azizkhani m.azizkhani@ausmt.ac.ir Yes Faculty of Veterinary Medicine, Amol University of Special Modern Technologies, Amol, Iran F. Tooryan No Faculty of Veterinary Medicine, Amol University of Special Modern Technologies, Amol, Iran