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

To investigate the influence of reducing beef surface water activity (aw) on the survival of Salmonella Typhimurium DT104 during heating. 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. A decrease in beef surface aw can substantially enhance the survival of S. Typhimurium DT104 after heating. 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.