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Applied and Environmental Microbiology, January 2001, p. 133-141, Vol. 67, No. 1
Department of Food Science, University of
Wisconsin
Received 12 July 2000/Accepted 8 October 2000
Probabilistic models were used as a systematic approach to describe
the response of Escherichia coli O157:H7 populations to combinations of commonly used preservation methods in unpasteurized apple cider. Using a complete factorial experimental design, the effect
of pH (3.1 to 4.3), storage temperature and time (5 to 35°C for 0 to
6 h or 12 h), preservatives (0, 0.05, or 0.1% potassium sorbate or sodium benzoate), and freeze-thaw (F-T;
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.1.133-141.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Modeling of Combined Processing Steps for Reducing
Escherichia coli O157:H7 Populations in Apple
Cider
Madison, Madison, Wisconsin
53706-1565,1 and Food Risk Analysis
Initiative, Rutgers University, New Brunswick, New Jersey
08901-85202
20°C, 48 h and
4°C, 4 h) treatment combinations (a total of 1,600 treatments) on the probability of achieving a 5-log10-unit reduction in
a three-strain E. coli O157:H7 mixture in cider was
determined. Using logistic regression techniques, pH, temperature,
time, and concentration were modeled in separate segments of the data
set, resulting in prediction equations for: (i) no preservatives,
before F-T; (ii) no preservatives, after F-T; (iii) sorbate, before
F-T; (iv) sorbate, after F-T; (v) benzoate, before F-T; and (vi)
benzoate, after F-T. Statistical analysis revealed a highly significant (P < 0.0001) effect of all four variables, with cider
pH being the most important, followed by temperature and time, and
finally by preservative concentration. All models predicted 92 to 99% of the responses correctly. To ensure safety, use of the models is most
appropriate at a 0.9 probability level, where the percentage of false
positives, i.e., falsely predicting a 5-log10-unit
reduction, is the lowest (0 to 4.4%). The present study demonstrates
the applicability of logistic regression approaches to describing the
effectiveness of multiple treatment combinations in pathogen control in
cider making. The resulting models can serve as valuable tools in
designing safe apple cider processes.
*
Corresponding author. Mailing address: Department of
Food Science, University of Wisconsin
Madison, 1605 Linden Dr.,
Madison, WI 53706. Phone: (608) 265-4801. Fax: (608) 262-6872. E-mail: scingham{at}facstaff.wisc.edu.
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