Background and Objectives: Doogh is an Iranian preferred dairy drink, especially in warm seasons. Blowing by yeasts is a common occurring spoilage when this product is kept outside the refrigerator in warm temperature. Natural additives such as herbal essential oils, which also induce the desired flavor and color, may solve this problem and retard yeast growth. Spearmint, pennyroyal and some other herbs and their extracts were traditionally used in this product. In the current study, the antimicrobial effect of Mentha spicata and Mentha pulegium essential oils on the survival of Debaryomyces hansenii was evaluated in two different storage temperatures.

Materials and Methods: Iranian Doogh was prepared according to the national standard method with different concentrations of the mentioned essential oils. Then all the samples were inoculated with yeast inocula to achieve a yeast count of >3×10⁶ CFUml^-1. Viability of Debaryomyces hansenii was investigated during the storage time (0-28 days) of Doogh samples at 4°C and 25°C at different intervals. Statistical analysis was performed using the one-way Analysis of Variance and Tukey’s post hoc methods. Also α level was considered equal to 0.05.

Results and Conclusion: Different concentrations of Mentha spicata and Mentha pulegium essential oils had significant effect on the growth of the yeast. Increasing the concentration of these essential oils decreased the logarithm of number of microorganisms. The essential oils of Mentha spicata and Mentha pulegium in low concentrations have antimicrobial effect on spoilage yeast and can improve the sensory properties of Doogh. Therefore, they can be the best alternative preservatives for hazardous chemical compounds.