P3-64 Thermal Inactivation of Escherichia coli O157:H7 and Non-O157:H7 Shiga Toxin-producing E. coli in Moisture Enhanced Non-intact Beefs as Affected by Internal Temperature, Moisture Enhancing Rate, and Resting Time by Double Pan-broiling

Wednesday, August 6, 2014
Exhibit Hall D (Indiana Convention Center)
Courtney Broyles, Western Kentucky University, Bowling Green, KY
Ellen Vice, Western Kentucky University, Bowling Green, KY
Russell McKeith, Western Kentucky University, Bowling Green, KY
Amanda McKeith, Western Kentucky University, Bowling Green, KY
Cangliang Shen, Western Kentucky University, Bowling Green, KY
Introduction: Escherichia coli O157:H7 (ECOH) or Non-O157 Shiga toxin-producing E. coli (STEC) may translocate from the meat surface to internal tissue during non-intact beef moisture enhancement (ME) process. Limited information is available regarding the thermal inactivation of Non-O157 STEC on moisture enhanced non-intact beefs.

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.