The 5 log pathogen reduction standard must be applied to the most resistant pertinent pathogen present on the fruit or in the juice. For most juices, this requires that the standard be applied after the juice is expressed. The surface skin of many fruits and vegetables is an imperfect barrier to microorganisms . Internalization is particularly problematic for fruit such as apples. Temperature differentials between wash water and fruit clearly exacerbate pathogen internalization . However, even in undamaged apples without the assistance of a temperature differential, pathogens have been shown to internalize through the floral tube and other structures or defects. Surface interventions such as washing or treating with chlorine or hydrogen peroxide solutions do not typically result in complete destruction of pathogens [68-73]. Ozone (Table 9.3) was similarly unsuccessful in destroying E. coli O157:H7 inoculated onto apples.
Surface treatments such as with ethanol or heat can result in greater than 5 log reductions in pathogens when the pathogens are spot inoculated onto the surface of apples (Table 9.3). However, when apples are inoculated by immersion, without any temperature differential between the fruit and the inoculum menstruum, surface treatments fail. Surface heat treatment applied to apples inoculated by immersion into an inoculum menstruum achieved
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