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Polyphenol oxidase (PPO) has been considered as an indicator of adequate heat treatment of apple juice. This enzyme ispresent within all apples, and is stable over a wide range of temperatures. Thermal stability varies with pH, but heating at temperatures above 70 C has been shown to reduce the enzyme activity to undetectable levels. Thus, the objectives of this project are to determine whether the thermal stability of PPO activity can serve to verify adequate pasteurization of apple cider, and to develop a rapid method for validating pasteurization effectiveness based on an understanding of the mechanism of PPO activity.
Fresh apple cider has been associated with recent outbreaks of foodborne illness. The FDA has responded to these outbreaks by requiring a warning label on cider unless the juice has been processed to receive a 5-log reduction in the target microorganisms.Research conducted in the investigator's laboratory has confirmed that Escherichia coli O157:H7 would be the most appropriate target organism. Pasteurization treatments of 71.1 C/6 sec and 68.1 C/14 sec have been validated as processes obtaining a 5-logreduction in E. coli O157:H7. Thermal pasteurization of cider would undoubtedly be a key step within any HACCP program. However, no rapid or economical method exists to verify that cider was adequately pasteurized. The results of this project will lead to a test that the cider industry and regulatory communities can use to verify safety of thermally pasteurized apple cider.