Effects of steam pasteurisation on Salmonella Typhimurium DT104 and Escherichia coli O157:H7 surface inoculated onto beef, pork and chicken

This study investigated the effectiveness of steam in the decontamination of beef, chicken and pork. Discs of each meat type were surface inoculated with log10 7–8 cfu/cm2Salmonella Typhimurium DT104 or Escherichia coli O157:H7 and treated with steam for up to 60 s in an experimental test apparatus. Treated discs were examined by a selective overlay resuscitation method to determine surviving pathogen numbers. After treatment for 60 s, numbers of surviving E. coli O157:H7 were generally higher than S. Typhimurium DT104, though significantly so only for chicken skin, indicating a possible difference in the heat resistance of the two organisms. The numbers of surviving cells were also influenced by meat type, treatment temperature and time. Significant variations in surviving cell numbers, were observed between replicates. The overall pattern of E. coli O157:H7 deactivation was clearly biphasic on all meat types, displaying an initial pattern of rapid decline within the first 10 s, followed by much slower decline during the remaining 50 s. This indicated the persistence of a heat resistant sub population of this pathogen. The data are discussed in relation to the heat resistance of bacterial cells and populations, and the implication of such resistance in the overall efficiency of steam decontamination on meat surfaces.