Thermal resistance of shiga toxin-producing Escherichia coli, Salmonella and Enterococcus faecium in peanut butter, oatmeal raisin, and chocolate chip cookies

Abstract

Thermal-death-time characteristics, D and z-values of shiga toxin-producing Escherichia coli (STEC), Salmonella, and Enterococcus faecium NRRL B-2354 were investigated in peanut butter, oatmeal, and chocolate chip cookie formulations at three moisture levels. E. faecium was shown to be more resistant than Salmonella, followed by E. coli at all water activity levels. E. faecium was at least 1.5 times more heat resistant compared to Salmonella under the same moisture and temperature conditions for all cookie formulations. The E. faecium to Salmonella ratio was larger at higher moisture levels. E. faecium was found to be suitable as a surrogate for Salmonella in validating soft cookie baking. Among the three formulations, Salmonella was the most heat resistant in peanut butter cookies. At the lowest moisture and water activity level (8% moisture, aw 0.421) of peanut butter cookies the D-values for E. coli were 14.01, 3.56, 1.73 min at 65, 70, 75 °C, while the D-values for Salmonella were 4.97, 2.59, 1.23 min, and for E. faecium were 15.50, 5.02, 2.02 min at 75, 80, and 85 °C, respectively. The z-values for E. coli, Salmonella, and E. faecium, were 11.02, 16.45 and 11.31 °C, respectively.