Purpose: The objective of this study was to determine the thermal inactivation kinetic parameters for non-O157 STEC strains and compare them to O157:H7 STEC on raw and fully-cooked meat products.
Methods: Five strains of individually grown O157:H7 or non-O157:H7 STEC were combined into two separate cocktails containing 8 log CFU/ml. Inocula were spread onto the surface of a 3.8 cm diameter circle of turkey deli meat or mixed with ground beef. Both samples were held for 30 min and then placed into vacuum-sealed polyethylene-nylon bags. Bags were submerged in a circulating-water bath at 56°C, 58°C or 60°C for various times, removed and cooled in an ice bath. Products were blended, serially diluted, and samples spread-plated on tryptic soy agar plates. Surviving bacteria from three replicate experiments were enumerated after 24h incubation at 37°C. D- and z-values were calculated using linear regression.
Results: In deli meat at 56, 58 and 60°C, D-values were 15.42 ± 0.08, 5.23 ± 0.16 and 1.89 ± 0.27 min for O157:H7 STEC, and 15.48 ± 1.0, 7.20 ± 0.56 and 2.86 ± 0.22 min for non-O157:H7 STEC, respectively. In ground beef at 56, 58 and 60°C, D-values were 11.85 ± 0.93, 5.66 ± 0.05, 1.55 ± 0.04 min for O157:H7 STEC, and 10.59 ± 1.59, 3.30 ± 0.25, 1.39 ± 0.29 min for non-O157:H7 STEC, respectively. z-values for O157:H7 and non-O157:H7 STEC in deli meat were 4.39 ± 0.31 and 5.46 ± 0.14°C, respectively, and in ground beef 4.54 ± 0.24 and 4.54 ± 0.15°C, respectively.
Significance: Composition of food influences the thermal inactivation parameters for O157:H7 and non-O157 E. coli. These data will help in designing adequate thermal processes to inactivate pathogenic E. coli in meat products.