Infrared Thermal Image Processing Technique for Evaluating Superheated Steam as a Dry Sanitation Method

Abstract The objectives of this study were to develop a thermal image analysis method for assessing the surface temperature of stainless steel (30 cm × 30 cm) during pilot-scale superheated steam sanitation and evaluate the sanitation efficacy based on the inactivation of Enterococcus faecium . An infrared camera, calibrated to a root-mean-square error (RMSE) of 1.4 °C within a range of 25 °C and 250 °C, was utilized. The results showed that the surface temperature at the impingement point decreased linearly from 245.6 ± 3.2 to 157.6 ± 1.7 °C as the nozzle-to-surface distance was increased from 2 to 5 cm. Furthermore, at a 2 cm nozzle-to-surface distance, temperatures swiftly dropped from 245.6 ± 3.2 to 95.8 ± 6.0 °C as the radial distance increased from 0 to 10 cm. In the stagnation region (0–1 cm radial distance), where the steam jet directly contacts the surface, the time required to achieve a 3-log reduction of E. faecium was reduced from 3 to 1 min as the nozzle-to-surface distance decreased from 5 to 2 cm. The efficacy of superheated steam sanitation was further evaluated under practical sweeping conditions, demonstrating a 2.7 ± 0.4 log reduction of E. faecium on a 900 cm 2 stainless steel surface within 10 min. This study thus highlights the potential use of thermal image analysis for optimizing superheated steam sanitation processes, particularly in dry food processing environments.