Survival of multidrug-resistant Salmonella typhimurium DT104 in egg powders as affected by water activity and temperature

A study was done to determine if a four-strain mixture of multidrug-resistant Salmonella typhimurium definitive type 104 (DT104) cells and a four-strain mixture of S. typhimurium non-DT104 cells differed in ability to survive in whole egg powder, whole egg powder supplemented with corn syrup solids (38%) and salt (1.9%), egg yolk powder, and egg white powder as affected by aw (0.29–0.37 and 0.51–0.61) during storage at 13 or 37°C for 8 weeks. Rates of inactivation of S. typhimurium DT104 and non-DT104 cells were similar within each set of test parameters. With the exception of whole egg powder supplemented with corn syrup solids and salt, death was enhanced at aw 0.29–0.37 compared to aw 0.51–0.61 when powders were stored at 13°C. Survival of cells in whole egg powder supplemented with corn syrup solids and salt was significantly (P≤0.05) higher compared to survival in other egg powders stored at 13°C. The opposite trend occurred in powders at aw 0.51–0.61 stored at 37°C. Survival of S. typhimurium DT104 and non-DT104 cells at initial populations of 5.01–5.39 log10 cfu/g of egg white powder containing 4.9, 6.1, or 8.2% moisture at 54 or 82°C for 7 days or 8 h, respectively, was determined. Rates of inactivation of DT104 and non-DT104 cells did not differ. Both cell types were detected in egg white powder containing 4.9% moisture but not in powder containing 8.2% moisture when held at 54°C for 7 days. Heating at 82°C for 8 h failed to eliminate 5 log10 S. typhimurium per g of egg white powder, regardless of the moisture content.