THERMAL INACTIVATION OF ESCHERICHIA-COLI O157-H7, SALMONELLA SENFTENBERG AND ENZYMES WITH POTENTIAL AS TIME-TEMPERATURE INDICATORS IN-GROUND TURKEY THIGH MEAT

The USDA Food Safety and Inspection Service has proposed to amend cook ing regulations to require that any thermal process used for poultry p roducts be sufficient to cause a 7 D reduction in salmonellae. Several enzymes have been suggested as potential indicators of heat processin g in poultry, yet no relationship between the inactivation rates of th ese enzymes and salmonellae has been determined. The thermal inactivat ion kinetics of endogenous muscle proteins, Escherichia coli O157:H7 a nd Salmonella senftenberg were compared in ground turkey thigh meat in thermal death time studies. Bacteria counts were determined and muscl e extracts were assayed for residual enzyme activity or protein concen tration. D and z values were calculated using regression analysis. S. senftenberg had higher D values at all temperatures and was more heat resistant than E. coli. The z values of E. coli on Petrifilm Coliform Count plates and phenol red sorbitol agar plates were 6.0 and 5.7 degr ees C, respectively. The z values of S. senftenberg were 5.6 and 5.4 d egrees C on Petrifilm and agar, respectively. Lactate dehydrogenase (L DH) was the most heat stable protein at 64 degrees C. LDH, glyceraldeh yde-3-phosphate dehydrogenase, creatine kinase, triose phosphate isome rase (TPI), acid phosphatase, serum albumin, and immunoglobulin G had z values of 3.8, 4.3, 4.8, 5.8, 6.3, 6.7, and 8.6 degrees C, respectiv ely, in turkey containing 4.3% fat. The z values for TPI decreased to 5.4 degrees C in thigh meat containing 9.8% fat. Temperature dependenc e of TPI was most similar to that of S. senftenberg, suggesting it mig ht function as an endogenous time-temperature integrator to monitor ad equacy of processing when a performance standard based an this pathoge n is implemented.