Influence of spore and carrier material surface hydrophobicity on decontamination efficacy with condensing hydrogen peroxide vapour

Aims: To investigate the influence of surface hydrophobicity of carrier material (CM) and bacterial spores of Bacillus subtilis SA 22 and Bacillus atrophaeus (DSM 675) on spore inactivation with condensing hydrogen peroxide (H₂O₂) gas. Methods and Results: Surface hydrophobicity of bacterial spores and CM was determined by means of contact angle measurement. Spores of B. subtilis showed water contact angles of 90°, spores of B. atrophaeus showed water contact angles of 42°. Above that, a resistance test against liquid H₂O₂ at room temperature was conducted with resulting values of 101 s (B. subtilis) and 906 s (B. atrophaeus). The spores were deposited on CMs of different wettability (water contact angles of 115–30°). The spores were applied either individually or as an 1 : 1 mixture of both spore species. Exposure of biological indicators (BI) with 5200 ppm of gaseous H₂O₂ at 70°C treatment temperature for defined times up to 10 s led to inactivation kinetics. Surfaces with high hydrophobicity showed faster spore inactivation than surfaces with lower hydrophobicity for single-spore species. Regarding the mixed BI, better survival of hydrophobic spores was expected. However, this effect can only be seen as a slight trend and is not significant after 10 s. Conclusions: Surface hydrophobicity of CMs does influence the decontamination with gaseous, condensing H₂O₂. However, surface hydrophobicity of spores in a mixed population does only have a small influence on inactivation results. Significance and Impact of the Study: The intensity of spore inactivation depends more on other factors than on the wettability of the bacterial spores. However, hydrophobic surfaces lead to faster inactivation effects and should thus be preferred for aseptic packaging technology.