Inactivation of Enterococcus faecium and Geobacillus stearothermophilus spores on stainless steel through dry sanitation approaches using superheated steam and ultraviolet C-LED

This study investigated the individual and sequential effects of UV-C radiation and superheated steam (SHS) on the inactivation of Enterococcus faecium and Geobacillus stearothermophilus spores, inoculated either directly or as thin food residue (wheat flour and dry milk) on stainless steel surfaces. Stainless steel sanitized with SHS alone at 180 degrees C achieved a 5-log CFU/cm2 reduction within 40 s for E. faecium and within 600 s for G. stearothermophilus spores. UV-C irradiation at 256 nm inactivated both microorganisms on stainless steel surfaces, achieving a 5-log reduction of E. faecium at 100 mJ/cm2 and a 3-log reduction of G. stearothermophilus at 500 mJ/cm2. However, the presence of food residues diminished the sanitizing efficacy of UV-C, resulting in a reduction of less than 1.2 log CFU/cm2 for both E. faecium (100 mJ/cm2) and G. stearothermophilus (500 mJ/cm2). SHS pretreatment increased the UV absorbance of food residues through Maillard reactions, limiting the effectiveness of UV-C. Nevertheless, UV-C pretreatment (5 and 10 mJ/cm2 for E. faecium and G. stearothermophilus) followed by SHS had an additive effect. This sequential treatment resulted in more than a 5-log reduction for E. faecium within 30 s and for G. stearothermophilus within 500 s of SHS treatment.