Purpose: This project aimed to develop novel interventions for E. coli on carcasses by studying the effects of temperature and water activity (aw) changes on carcass surfaces during air chilling to identify whether the lethal effects can be enhanced.
Methods: Exponential phase E. coli O157:H7 strain Sakai were subjected to simultaneous rapid downshifts in temperature and aw, from 35°C aw 0.993 to 14°C aw 0.967 in a nutrient broth. Responses of E. coli were analysed by viable count; changes in its proteome were characterised by 2D-LC/MS/MS analysis. In subsequent studies, an oxidant (i.e., hydrogen peroxide or chlorine dioxide; both at 75 ppm) was applied at different phases of E. coli growth during exposure to the combined shifts (i.e., 1h, 8h and 25h after the shifts) and changes in E. coli numbers determined.
Results: Exposure of E. coli to abrupt downshifts in temperature and aw albeit to non-lethal conditions produced a complex pattern of population change which could be divided into three phases including inactivation and recovery phases. Proteomic analysis revealed a transient decrease in several proteins involved in oxidative stress responses during the early response phase. Subsequent trials confirmed that E. coli subjected to the environmental shifts became more susceptible to oxidative damage during the early phase of the response when compared to later phases.
Significance: The present results highlight the potential application of oxidants at appropriate time during air chilling to control or eliminate E. coli on carcasses.