Utilizing superheated steam to inactivate Enterococcus faecium NRRL B-2354 on various material surfaces used in food and produce industries

Traditional sanitation in dry food and produce manufacturing plants is challenging as residual moisture can harbor microbial contamination. Superheated steam (SHS) is produced when water is heated to temperatures (125–400 °C) beyond the boiling point. SHS does not lead to condensation on surfaces. There are limited studies available on the sanitation efficacy of SHS on different surfaces. This study was conducted to understand the sanitation efficacy of SHS to inactivate Enterococcus faecium NRRL B-2354 on different surfaces (stainless steel, concrete, plywood, leather, polytetrafluoroethylene (PTFE), silicon rubber, cotton, and cardboard). The surfaces were either spot inoculated or coated with a representative food matrix (baby formula) and treated with SHS at 150 °C for a total process time (come-up time + treatment time) of 3 min. Spot-inoculated surfaces showed a higher microbial inactivation (range: 9.2 ± 0.9 to 10.7 ± 0.7 log reduction/coupon) whereas surfaces with inoculum coated with baby formula had lower microbial inactivation (range: 7.8 ± 0.4 to 9.6 ± 0.4 log reduction/coupon). The effects of surface characteristics like thermal inertia, surface roughness, and hydrophobicity of microbial inactivation were studied. Prolonged usage of SHS (150 °C for 5 min once a week over 8 weeks) did not alter surface characteristics, particularly roughness of stainless steel, silicone rubber and plywood.