Acid adaptation and temperature effect on the survival of E. coli O157:H7 in acidic fruit juice and lactic fermented milk product.
In this study, two strains of Escherichia coli O157:H7, (ATCC 43889 and ATCC 43895) were acid adapted at pH 5.0 in tryptic soy broth (TSB) for 4 h. Commercial products of mango juice (pH 3.2), asparagus juice (pH 3.6), Yakult--a diluted milk fermented drink (pH 3.6), and low-fat yoghurt (pH 3.9) were inoculated with acid-adapted or nonadapted cells of E. coli O157:H7. Survival of the inoculated E. coli O157:H7 in these commercial food products during storage at 25 or 7 degrees C was examined. It was found that although survival of the acid-adapted and nonadapted E. coli O157:H7 ATCC 43895 in asparagus juice during storage at 7 degrees C did not show marked difference, in general, acid adaptation and low temperature enhanced the survival of E. coli O157:H7 in both the commercial fruit juices tested. On the contrary, acid adaptation reduced the survival of both the strains of the test organism in Yakult and low-fat yoghurt stored at 7 degrees C. Besides, E. coli O157:H7 ATCC 43895 survived longer than ATCC 43889 in all the products examined, regardless of the storage temperature and acid adaptation.
Hsin-Yi
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Graduate Institute of Food Science and Technology, National Taiwan University, Taipei.
Chou
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CC
D000222:Adaptation, Physiological; D000818:Animals; D001628:Beverages / Q000382:microbiology*; D003611:Dairy Products / Q000382:microbiology*; D019453:Escherichia coli O157 / Q000254:growth & development / Q000502:physiology*; D005285:Fermentation; D005511:Food Handling; D005638:Fruit / Q000382:microbiology; D006863:Hydrogen-Ion Concentration; D008892:Milk / Q000382:microbiology; D013696:Temperature; D013997:Time Factors; D015014:Yogurt / Q000382:microbiology