Purpose: Quantify the effect of heat on the fate of ECOH and STEC in a model beef system.
Methods: For each of two trials, freshly-ground beef of higher (70:30 = percent lean:fat) or lower (93:7 = percent lean:fat) fat content was inoculated separately with a single strain of E. coli serotypes O111:H-, O45:H2, O103:H2, O121:H19, O145:NM, O26:H11, and O157:H7 to ca. 7.0 log CFU/g. Next, 3-g samples were transferred into filter bags. With the aid of a stainless-steel roller, the meat was flattened (ca. 1.0 mm) within the bags and then vacuum-sealed. For each target temperature and time point, three bags were submerged in a thermostatically-controlled water bath and heated to an internal temperature of 54.4 °C for up to 90 min, or 60 °C for up to 4 min, or 65.6 °C for up to 0.5 min. Note, the safe cooking guidance for raw beef products generally is above 62.8 °C.
Results: D-values decreased as the heating temperature increased. In lower fat wafers, D-values ranged from 13.7 to 23.8 min, 0.86 to 1.33 min, and 0.19 to 0.22 min at 54.4 °C, 60 °C, and 65.6 °C, respectively. Heating higher fat wafers to 54.4 °C, 60 °C, or 65.6 °C generated D-values of 20.4 to 32.7 min, 0.83 to 1.22 min, and 0.18 to 0.34 min, respectively. In general, with the exception of wafers heated to 54.4 °C, no effect of fat level on lethality of STEC and ECOH and no appreciable differences in thermal inactivation among STEC serotypes and between STEC and ECOH were observed.
Significance: These data established that cooking times/temperatures effective for inactivating ECOH in ground beef are equally effective against the additional STEC strains investigated.