Influence of Superheated Steam Temperature and Moisture Exchange on the Inactivation of Geobacillus stearothermophilus Spores in Wheat Flour-Coated Surfaces

Sanitation in dry food processing environments is a major challenge for the industry. The influence of superheated steam (SH) temperatures (125 to 250 degrees C) on the inactivation of spores on selected coupon surfaces (stainless steel, rubber, and concrete) coated with wheat flour as a model food soil residue was investigated using a bench scale superheating apparatus. Wheat flour inoculated with Geobacillus stearothermophilus (7.62 +/- 0.12 log CFU/g) coated on the coupon surfaces served as the model food residue. Among the surfaces tested, temperature of concrete increased faster [time constant (tau) < 89.0 s] than that of stainless steel (tau < 173.6 s). As a consequence, wheat flour coated on concrete dehydrated faster [moisture diffusivity (D-m) > 1.17 x 10(-4) mm(2)/s] than those on the stainless steel (D-m > 0.76 x 10(-4) mm(2)/s). Hence, Geobacillus stearothermophilus spores suspended on stainless steel were inactivated faster than that of concrete and rubber (p < 0.05). The time required for a 5-log reduction at 250 degrees C were 180 s and 240 s, on stainless steel and concrete surfaces, respectively. A mathematical model that considered surface temperature, food residue moisture content, and SH inversion temperature adequately described spore inactivation during SH treatment.