Purpose: The objective of this study was to compare the thermal resistance of individual cocktails of O157 STEC, emerging big six non-O157 STEC, and Salmonella enterica in fettuccine with alfredo sauce using linear and Weibull models.
Methods: Five-strain cocktails with ca. 8 log CFU/ml were added to a 1:1 mixture of fettuccine pasta and alfredo sauce, stored for 30 min and placed into vacuum-sealed bags. Bags were immersed in a recirculating water-bath at 56°C, 58°C or 60°C (temperatures and come-up times were monitored), removed at various time intervals, and immediately cooled in an ice-bath. Stomached samples were serially diluted and spread-plated on Tryptic Soy Agar plates. Surviving bacteria from triplicate experiments were enumerated after 24 h at 37°C.
Results: Calculated D-values from the first-order model (56 to 60°C) were 6.40 ± 1.67 to 1.19 ± 0.19 min for O157 STEC, 7.02 ± 0.64 to 1.26 ± 0.24 min for non-O157 STEC and 3.75 ± 0.39 to 0.46 ± 0.03 min for Salmonella. Using the Weibull model, the tD values needed to destroy 1 log (56 to 60°C) ranged from 5.28 ± 1.52 to 1.31 ± 0.41, 6.00 ± 0.59 to 1.49 ± 0.37, and 3.08 ± 0.54 to 0.37 ± 0.09 min for O157 STEC, non-O157 STEC and Salmonella, respectively. Using D-values and tD values, the z-values were 5.47 ± 0.29, 5.36 ± 0.79 and 4.42 ± 0.33°C for O157, non-O157 and Salmonella, respectively, by the first-order model; and 6.62 ± 1.43, 6.60 ± 0.98 and 4.34 ± 0.14°C for O157, non-O157 and Salmonella, respectively, by the Weibull model.
Significance: Statistical analysis of these results show that the Weibull model is a better fit for describing the thermal inactivation of some pathogens (STEC in this study), but there was no difference between the two models in the case of S. enterica.