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

The USDA has established processing schedules for beef products based on the destruction of pathogens. Several enzymes have been suggested a s potential indicators of heat processing. However, no relationship be tween the inactivation rates of these enzymes and those of pathogenic microorganisms has been determined. Our objective was to compare the t hermal inactivation of Escherichia coli O157:H7 and Salmonella senften berg to those of endogenous muscle proteins. Inoculated and noninocula ted ground beef samples were heated at four temperatures for predeterm ined intervals of time in thermal-death-time studies. Bacterial counts were determined and enzymes were assayed for residual activity. The D values for E. coli O157:H7 were 46.10, 6.44, 0.43, and 0.12 min at 53 , 58, 63, and 68 degrees C, respectively, with a z value of 5.60 degre es C. The D values for S. senftenberg were 53.00, 15.17, 2.08, and 0.2 2 min at 53, 58, 63, and 68 degrees C, respectively, with a z value of 6.24 degrees C. Apparent D values at 53, 58, 63, and 68 degrees C wer e 352.93, 26.31, 5.56, and 3.33 min for acid phosphatase; 6968.64, 543 .48, 19.61, and 1.40 min for lactate dehydrogenase; and 3870.97, 2678. 59, 769.23, and 42.92 min for peroxidase; with z values of 7.41, 3.99, and 7.80 degrees C, respectively. Apparent D values at 53, 58, 63, an d 66 degrees C were 325.03, 60.07, 3.07, and 1.34 min for phosphoglyce rate mutase; 606.72, 89.86, 4.40, and 1.28 min for glyceraldehyde-3-ph osphate dehydrogenase; and 153.06, 20.13, 2.25, and 0.74 min for trios e phosphate isomerase; with z values of 5.18, 4.71, and 5.56 degrees C , respectively. The temperature dependence of triose phosphate isomera se was similar to those of both E. coli O157:H7 and S. senftenberg, su ggesting that this enzyme could be used as an endogenous time-temperat ure indicator in beef products.