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Chemical preservatives are usually used to reduce or eliminate pathogenic or spoilage microorganisms but their inordinate applications have resulted in toxigenic residuals and adverse effects on consumers, So many researches have been done to substitute the chemicals with naturally occurring compounds, especially plant essential oils. In this study, the chemical compositions of essential Thymus kotschyanus were identified with set GC-MS. Then organoleptic properties, microbial and physicochemical quality of Doogh sample prepared with adding different concentration Thymus kotschyanus essential oil were investigated during 14 day storage. Results of GC-MS analysis indicated that thymol (51.1 %), p-cymene (13.78 %) and γ-terpinene (9.03 %) comprised the highest amount of this EO. T. kotschyanus EO destroyed E.coli O157:H7 in addetive low concentrations to Doogh in same the early days and the MIC that  determined by the micro dilution method was 470µg/ml. Based on the results, essential oil doesn’t have significant changes in Doogh physico-chemical properties excepion total solid that essentail Doogh free comparsion with Doogh contain 100 and 200 ppm make significant changes(p<0.05), the Doogh that contain 50 ppm was accepted by panelist. The addition of this EO has no adverse effect on the physicochemical and organoleptic properties of Doogh, also this EO effective substances could be purified and used as natural antibacterial agent, solely or along with others techniques, to prolong food shelf life.

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Heating at high temperatures creates a large change in the chemical properties of oils. Due to effects of oils on health, further research is necessary to choose the best type and quality of oils. Extra virgin olive oil is considered one of the best due to the beneficial effects of dietary oils. The aim of this study was to compare the thermal stability of Iranian and foreign extra virgin olive oil. Eight samples of olive oil were tested in this study. Oils were heated at 120 ° C for 4 h to evaluate the thermal stability, were sampled every 2 hours. Fatty acid composition, Acid value, Peroxide value, Anisidine value, Totox value, Rancimat oxidative stability test, was conducted in accordance with Iranian national standards. Results showed that oleic acid, the major fatty acid in olive oil, was between 69 to 74 percent. There was a significant relationship between time and acid value (P= 0/013), peroxide value (P≤ 0/001), anisidine value (P≤ 0/001), totox value (P≤ 0/001). There was not observed any significant relationship between changes in oil and acid value, peroxide value, anisidine value, but with totox value (P= 0/003) a significant relationship was observed. Interpretation of the data suggests that the thermal process changes the index of acidity, peroxide, anisidine and totox. The changes will further increase with time. According to the obtained results,foreign  extra virgin olive oils are better and are more resistant to heat than Iranian ones.