Effect of heating rate on thermal inactivation kinetics of Escherichia coli O157:H7 in ground beef

Abstract

The objective of this study was to investigate the effect of heating rate on thermal inactivation kinetics of microorganisms in food, testing the survival of Escherichia coli O157:H7 in ground beef during isothermal and dynamic heating. A 4-strain cocktail of E. coli O157:H7 was inoculated to irradiation-sterilized ground beef (10 % fat) and then subjected to isothermal heating (55-63 °C) and dynamic heating (20-63 °C). One-step analysis was used to determine the kinetic parameters. Different degrees of increased thermal resistance were observed in E. coli O157:H7 during dynamic heating. In comparison to isothermal heating, slight increase in the thermal resistance was found during fast heating (1.2-1.8 °C/min). However, slow heating (0.3-0.9 °C/min) led to significantly increased thermal resistance due to heat adaption at temperatures below 61.3 °C, but E. coli O157:H7 became more sensitive to heat above this temperature, suggesting that the increased resistance may diminish after reaching a critical temperature. To account for the increased heat resistance during dynamic heating, a unified kinetic model was developed and validated by applying one-step dynamic analysis, resulting in more accurate kinetic parameters to describe the survival curves of all heating rates. This study demonstrated that the kinetic parameters derived from isothermal conditions may not be applicable to dynamic conditions. It is necessary to consider the effect of heating rate and to determine the thermal inactivation kinetic parameters under dynamic conditions. It also demonstrated the advantage of using one-step dynamic analysis for evaluating thermal processes. The results of this study may be particularly useful for designing slow-heating processes to ensure proper cooking of products.