Increasing awareness of the relationship between diet and disease has lead to greater emphasis on foods capable of meeting basic nutritional requirements while providing additional physiological benefits. Iran is the source of a large number of the medicinal plants that are currently in use throughout the country. These plants have great potential due to their prevalence, nutritive value and biologically active components. Despite these potentials, they have not found use in food products. There is a tremendous potential to add value to these medicinal plants by promoting them as a source of highvalue functional ingredients for use in food processing and preservation. Stachys lavandulifolia is widely used in Khorasan province as a herbal tea. It is used for the treatment of gastrointestinal and respiratory disorders. The aim of this study was to investigate the antimicrobial effect of Stachys lavandulifolia essential oil on growth of mold and yeast and total counts of bacteria. The essential oil of Stachys lavandulifolia which extracted by Clevenger apparatus was added in the levels of 0.001%, 0.003% and 0.005% to the pasteurized yoghurt drink samples which were packed in 250 ml containers. The samples stored at 4°C for 75 days and each 15 day subjected to microbial tests. The results showed the antimicrobial effect of different levels of essential oil was significant when compared with control group. The 0.001% level was effective in decreasing the growth and a significant difference was observed in treatments with 0.003 and 0.005%. However, there was no significant difference between the 60 and 75- days samples. Yoghurt drink samples that contain 0.005% essential oil showed more inhibitory effects against mold and yeast, and total counts of bacteria. According to the results of this study, it seems that essential oil of Stachys lavandulifolia has antimicrobial properties against mold, yeast and bacteria and it can be used not only as a flavoring agent but also as
