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Polyphenol Oxidase Activity as a Potential Intrinsic Index of Adequate Thermal Pasteurization of Apple Cider

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In response to increasing concerns about microbial safety of apple cider, the U.S. Food and Drug Administration has mandated treatment of cider sufficient for a 5-log reduction of the target pathogen. Pasteurization has been suggested as the treatment most likely to achieve a 5-log reduction, with Escherichia coli O157:H7 as the target pathogen. Regulators and processors need a reliable method for verifying pasteurization, and apple cider polyphenol oxidase (PPO) activity was studied as a potential intrinsic index for thermal pasteurization. The effect of pasteurization conditions and apple cider properties on PPO activity and survival of three pathogens (E. coli O157:H7, Salmonella, and Listeria monocytogenes) was studied using a Box-Behnken response surface design. Factors considered in the design were pasteurization conditions, i.e., hold temperature (60, 68, and 76°C), preheat time (10, 20, 30 s), and hold time (0, 15, 30 s), pH, and sugar content (°Brix) of apple cider. Response surface contour plots were constructed to illustrate the effect of these factors on PPO activity and pathogen survival. Reduction in PPO activity of at least 50% was equivalent to a 5-log reduction in E. coli O157:H7 or L. monocytogenes for cider at pH 3.7 and 12.5 °Brix. Further studies, however, are needed to verify the relationship between PPO activity and pathogen reduction in cider with various pH and °Brix values.


Document Type: Research Article

Affiliations: Department of Food Science, University of Wisconsin, Madison, Wisconsin 53706, USA

Publication date: May 1, 2004

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