Structure of deposits formed by drying of droplets contaminated with Bacillus spores determines their resistance to rinsing and cleaning

Abstract

The formation of deposits by evaporation of droplets contaminated by Bacillus spores was investigated, focusing on the role of spore and material properties. Droplets containing hydrophilic to hydrophobic spores were deposited on materials (stainless steels, polypropylene, glass). The presence of spores within the droplets, as well as material hydrophobicity plays a major role in the kinetics of the droplet shape during drying while the pattern of the dried deposit was affected by both material and spore properties. The resistance to detachment of the different deposits was then investigated. After a single rinsing procedure, a very high resistance to detachment of adherent spores was observed (up to 90% of residual spores). The hydrophilic Bs PY79 spores were the least resistant to removal, while the differences between materials were not pronounced. The ease of cleaning of the dried deposits was much greater. The least resistant spores were still the Bs PY79 ones, while the detachment was 3–100 times more effective on glass than on other materials. These results highlight the predominant role of hydrophilic/hydrophobic properties of particles and materials on the structure of deposits and their further resistance to rinsing and cleaning procedures.