Survival of Escherichia coli O157:H7 in dried beef powder as affected by water activity, sodium chloride content and temperature

A study was carded out to determine the rate of inactivation of Escherichia coli 0157:H7 in beef powder as affected by a(w) (0.34±0.06±0.01), sodium chloride content (0.5, 3.0 and 20%) and temperature (5 and 25°C) over an 8-week storage time. Retention of viability of acid-adapted, acid-shocked, and control cells was determined. Overall, there were no significant differences (P≤0.05) in survival among the three types of cells subjected to the same test parameters, suggesting that mechanisms associated with induction of acid adaptation or acid shock do not result in cross protection against dehydration or osmotic stresses. At each a(w) and within cell type, an increase in sodium chloride concentration resulted in significant reductions in the number of viable cells after a given storage time. Regardless of cell type, survival was significantly higher in beef powder containing 0.5 or 3% sodium chloride compared to powder containing 20% salt. The rate of inactivation was enhanced at a(w) 0.34±0.06 compared to a(w) 0.68±0.01 and at 25°C compared to 5°C.