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Applied and Environmental Microbiology, January 2001, p. 133-141, Vol. 67, No. 1
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

Heidi E. Uljas,1 Donald W. Schaffner,2 Siobain Duffy,2 Lihui Zhao,2 and Steven C. Ingham1,*

Department of Food Science, University of Wisconsin---Madison, Madison, Wisconsin 53706-1565,1 and Food Risk Analysis Initiative, Rutgers University, New Brunswick, New Jersey 08901-85202

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; -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.


Applied and Environmental Microbiology, January 2001, p. 133-141, Vol. 67, No. 1
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.1.133-141.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.



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Copyright © 2001 by the American Society for Microbiology. All rights reserved.