Abstract

Pathogenic outbreaks related to consumption of dry foods have encouraged scientific communities to study the thermal resistance of the surrogate for thermal pasteurization validation tests. The purpose of this study was to investigate thermo-tolerance relative to mRNA levels in E. coli ATCC 25922 in LB broth at three temperatures after previous heat shock, and analyze heat shock protein levels after preconditioning by using aluminum test cell. The results showed that D-values for E. coli decreased as the temperature increased from 57 to 63 °C. The enhanced thermo-tolerance was found when the culture was subjected to three sub-lethal temperatures and reached maximum level at 45 °C for 5 min. The trend of relative mRNA level and the enhanced HSP 70 protein further confirmed the increased D-values after heat shock treatments. After storage at cold or room temperatures for a day, however, the enhanced thermo-tolerance of E. coli ATCC 25922 could be eliminated. Necessitate longer times at a lethal temperature are needed to guarantee the required food safety in developing effective pasteurization processes.

Key words: E. coli; heat shock protein; preconditioning; thermal processing; thermo-tolerance