Purpose: This study evaluated the effect of ME rate, resting time on the inactivation of ECOH or Non-O157 STEC in reconstructed non-intact beefs cooked to various internal temperatures.
Methods: Fresh 1-kg coarse-ground beef knuckles, inoculated with ECOH (2-strain cocktail) or a mixture of Non-O157-STEC O26, O45, O103, O111, O121, and O145 (5.8 ± 0.1 log CFU/g), were mixed with NaCl+Na-tripolyphosphate solutions to reach a 10 or 18% ME rate. Semi-frozen beefs were cut into 2.54-cm thick, vacuum-packaged, frozen (-20°C, 96h), and tempered (4°C, 2.5h) before double pan-broiling (Farber-ware®griller) to internal temperatures of 55, 60, 65 and 71.1°C with 0.5 or 3.5-min rest. Temperatures of the griller and beefs were monitored with thermocouples. Samples were analyzed for survivors on tryptic soy agar and sorbitol MacConkey agar plus sodium pyruvate (0.1%). Colors of the internal cooked beef were also monitored. Data (two replicates/three samples each) were analyzed using the GLM model of SPSS including independent variables and interactions.
Results: ECOH and Non-O157 STEC behave similar (P = 0.518) to thermal treatments. Cooked internal temperature (P = 0.001) of 65 and 71.1°C achieved higher reductions (4.76-5.21 log CFU/g) compared to those of 55 and 60°C (2.43-3.53 log CFU/g) regardless of ME rate and resting time. 3.5-min resting time (P = 0.007) or 18%-ME (P = 0.008) achieved an additional 0.5 log CFU/g reduction among various internal temperatures. Similar internal colors of a* (7.39), b* (17.96), L* (48.57) (10%-ME) and a* (11.36), b* (15.11), L* (46.25) (18%-ME) were observed regardless of cooked internal temperatures.
Significance: These findings will be useful by USDA-FSIS to develop risk assessments of ECOH and Non-O157 STEC on non-intact and intact beef products.