The study on microbial flora and shelf life of pasteurized milk in Shiraz city, Fars province

This research with the aims of microbial flora determination in pasteurized milk and it’s shelf life study based on microbial and physicochemical parameters were performed within 10 days. In this study، 60 pasteurized milk samples randomly were selected and then total count of bacteria and total psychrophilic bacteria count were performed. To investigate microbial flora of pasteurized milk، colonies in each of the plates with different appearance were selected and transferred to a nutrient inclined medium agar inside tubes and incubated at 30 ºC for 24 hours. After 24 hours، individual colonies were investigated for shape، oxidase and catalase tests and gram staining. Depending on the needs، specific media and confirmation tests were used. Alkaline phosphatase، alcohol، acidity and pH tests and fat، protein، lactose، freezing point، moisture and specific gravity measurements were done daily on the milk samples. The results of this research showed that the total bacteria count of pasteurized milk was above the standard level of Iran after the seventh day of keeping and therefore their shelf lives in the refrigerator storage were determined maximum 6 days. Alcohol test was positive after the fifth day. The studied physicochemical factors showed no statistically significant differences during 10 days and were not found significant relationship between the studied physicochemical and microbiological parameters. Identified bacterial genus were Micrococcus، Lactobacillus، Bacillus، Corynebacterium and Pseudomonas. This study showed that the shelf life of pasteurized milk is low in Shiraz that could be due to high microbial load in primary raw milk.