Survival of Escherichia coli O157:H7 during the Manufacture and Storage of Fruit Yogurt

Abstract

The objectives of the study were to assess the behavior of Escherichia coli O157: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. coli O157:H7 and lactic acid bacteria (LAB) counts; pH of samples was recorded. During fermentation, E. coli O157:H7 grew in the presence or absence of LAB regardless of temperature. E. coli O157:H7 increased in presence of thermophilic LAB more than 2.75 log cfu/mL. The growth of LAB in all samples showed the same trend. The pH values of milk containing E. coli O157:H7 and LAB decreased gradually to reach 4.6 ± 0.1 at the end of fermentation period. During cooling, there was neither growth nor death of E. coli O157:H7 at 4 and 10C, while a slight increase at 15C. All the experiments showed significant differences in the population of E. coli O157:H7 in the presence or absence of LAB. During storage, E. coli O157:H7 number declined for all experiments and approached undetectable levels at the end of storage. The sensitivity of E. coli O157:H7 to acidity and lowered temperature was noticed during storage. Practical Applications Escherichia coli O157: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.