Nowadays, due to the public awareness about the adverse effects of temperature on the composition of processed foods, willingness of consuming natural food and beverages has increased. While using extreme heat is a strong strategy for inhibiting the growth of microorganisms and increasing the shelf-life of food, it would reduce the nutritional value. Hurdle technology is a novel approach for extending food shelf-life in which along with creating a moderate thermal process and a lateral process such as fermentation and applying essentials for achieving a same reliability as extreme thermal process. Doogh is a fermented beverage containing water and yogurt. Using bio preservatives in this drink not only moderate the thermal processing but also provide a probiotic food. Moreover, essential oils can do the same in addition to providing desirable flavor and nutritional properties. In this study the antimicrobial activity of essential oils and BLIS of lactobacillus Bulgaricus su. K41 and A was evaluated as a once and together associated with Oregano and sage. Doogh inoculated with Escherichia coli was heated for 1, 3, 5, 10 and 15 min at 75°C and the effect of heating time on reducing number of Escherichia coli was evaluated. In all treatments until 6 weeks no pathogens were observed whereas in Escherichia coli contaminated samples of strains A/K41 with 50:50 present, had a significant impact on reducing Escherichia coli logarithmic cycles in the seventh week. However, the dough samples of the yogurt which prepared by indigenous strains did not have significant difference with blank. Among sage and oregano, oregano was showed higher inhibitory effect. But the combination of this essential with indigenous strains A/K41 showed the most reduction of Escherichia coli logarithmic cycles in comparison to other treatments. Heating doogh containing cfu/ml Escherichia coli at 75°C for 15 min reduced the number of this bacterium under the standard level. In other treatments it was different depends on the heating time. Despite that using indigenous strains of K41 and A could highly extend the indigenous doogh shelf-life (12 weeks). However, its flavor was not acceptable for panelists but using essential especially oregano with indigenous strains of K41 and A solved this problem. Although thermal processing is an affective factor in reducing the number of Escherichia coli bacteria, it is possible to apply the combination of reducing heating time with using oregano essential and indigenous strain to obtain the same reliability index. Keywords : indigenous strains, Essential oils, Hurdle technology, thermal process, Doogh, probiotic
