Effects of reduction in beef surface water activity on the survival of Salmonella Typhimurium DT104 during heating

Aim: To investigate the influence of reducing beef surface water activity (aw) on the survival of Salmonella Typhimurium DT104 during heating.Methods and Results: Beef discs were surface inoculated with S. Typhimurium DT104 and either untreated or dried to achieve surface aw values of 0·95, 0·85 and 0·70. The samples were vacuum packed, heat-treated at 60°C and removed at predetermined times. The inactivation curves were influenced by aw and treatment time. Biphasic inactivation curves were observed for S. Typhimurium DT104 heat-treated on beef samples with altered aw values, which were characterized by an initial decline in cell numbers at commencement of heating followed by a much slower rate of inactivation during the remaining treatment period. Point estimates of the heating time required to achieve a 1 log reduction on beef surfaces with aw of 0·99, 0·95, 0·85 and 0·70 were 0·5, 1·55, 11·25 and 17·79 min, respectively.Conclusions: A decrease in beef surface aw can substantially enhance the survival of S. Typhimurium DT104 after heating.Significance and Impact of the Study: Caution needs to be taken using dry air as a decontamination method as this may rapidly decrease product surface and pathogen aw values resulting in enhanced survival.