Effect of meat binding formulations on thermal inactivation of Escherichia coli O157:H7 internalized in beef

This study evaluated the effects of meat binding or restructuring formulations, including salt/phosphate, algin/calcium, ActivaRM, and Fibrimex, with or without 0.27% (wt/wt) lactic acid, on thermal inactivation of internalized Escherichia coli O157:H7 in ground beef, serving as a model system for restructured products. Ground beef batches (700 g; approximately 5% fat) were mechanically mixed with a 5-strain composite of E. coli O157:H7 (7 log CFU/g) and then with the restructuring formulations. Product portions (30 g) were extruded into plastic test tubes (2.5 x 10 cm) and stored at 4 degrees C (18 h), before heating to 60 or 65 degrees C in a circulating water bath to simulate rare or medium-rare doneness of beef, respectively. Cooking to 60 or 65 degrees C reduced (P < 0.05) bacterial counts of control samples by 1.8 and 3.2 log CFU/g, respectively. Thermal destruction at 60 degrees C was not different (P > 0.05) among all treatments and the control. At 65 degrees C, greater (P < 0.05) thermal inactivation of E. coli O157:H7, as compared to the control, was obtained in samples treated with lactic acid alone (reductions of 4.9 log CFU/g), whereas for all other treatments, microbial destruction (reductions of 2.2 to 4.5 log CFU/g) was comparable (P > 0.05) to that of the control. Cooking weight losses were lower (P < 0.05) in salt/phosphate samples (<1%) compared to other formulations and the control (7.4% to 15.9%). Findings indicated that, under the conditions examined, restructuring of beef with salt/phosphate, algin/calcium, ActivaRM, or Fibrimex did not affect inactivation of internalized E. coli O157:H7 in undercooked (60 or 65 degrees C) samples, whereas inclusion of lactic acid (0.27%) in nonintact beef products enhanced pathogen destruction at 65 degrees C.