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

A study was carried out to determine the rare of inactivation of Escherichia coli O157: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 degrees 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 less than or equal to 0.05) in survival among the three types of cells subjected to the same rest parameters, suggesting that mechanisms associated with induction of acid adaptation or acid shock do nor 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 degrees C compared to 5 degrees C. (C) 1999 Academic Press.