SURVIVAL OF ESCHERICHIA COLI O157:H7 DURING THE MANUFACTURE AND STORAGE OF FRUIT YOGURT

The objectives of the study were to assess the behavior of Escherichia coliO157:H7 during the manufacture of fruit yogurt at different fermentation and storage temperatures. Reconstituted milk was fermented at 37, 40 or 45C; the resultant product was stored at 4, 10 or 15C for 7 days. Samples of milk and yogurt were analyzed. E.coliO157:H7 and lactic acid bacteria (LAB) counts; pH of samples was recorded. During fermentation, E.coliO157:H7 grew in the presence or absence of LAB regardless of temperature. E.coliO157:H7 increased in presence of thermophilic LAB more than 2.75logcfu/mL. The growth of LAB in all samples showed the same trend. The pH values of milk containing E.coliO157:H7 and LAB decreased gradually to reach 4.60.1 at the end of fermentation period. During cooling, there was neither growth nor death of E.coliO157:H7 at 4 and 10C, while a slight increase at 15C. All the experiments showed significant differences in the population of E.coliO157:H7 in the presence or absence of LAB. During storage, E.coliO157:H7 number declined for all experiments and approached undetectable levels at the end of storage. The sensitivity of E.coliO157:H7 to acidity and lowered temperature was noticed during storage. Practical ApplicationsEscherichia coliO157:H7 has emerged as a major foodborne pathogen and has been implicated in several outbreaks involving milk and dairy products. The results of the present study indicate that E.coli cannot tolerate the acidity and storage temperature. Applying quality control systems in the processing line will ensure that the E.coli will not survive in the commercially prepared fruit yogurt.