Hot water immersion to eliminate Escherichia coli O157:H7 on the surface of whole apples:: Thermal effects and efficacy

The effect of hot water immersion on both the reduction of Escherichia coli O157:H7 on the apple surface and internal temperatures of the apple was assessed in this study. Microbial reductions were measured experimentally, whereas internal temperatures were calculated through a mathematical analysis of experimental heat transfer data obtained from the apples. A method was developed to provide a purely surface-based inoculation of E. coli O157:H7. Rinsing produced no reduction, and treatments at 80 and 95 degreesC produced reductions of more than 5 logs in 15 s or less. The heat transfer analysis based on experimental data was used to calculate surface heat transfer coefficients and predict temperatures throughout the apple. The analysis indicated a low heat transfer rate. Although it reduces thermal degradation, a low heat transfer rate precludes thermal-based reduction of any internalized microorganisms.