Retention and removal mechanisms of bacterial surrogates on/from natural and model produce surfaces

Jin, YanBacterial contamination of fresh produce has been a significant concern for the food industry, the scientific community, and the public in recent years. A fundamental understanding of the interactions between produce surfaces and bacteria is critical for devising effective decontamination strategies. In this dissertation, the mechanisms leading to bacterial retention and removal were investigated in a model system comprised of colloids as bacterial surrogates, and polydimethylsiloxane (PDMS) replicas of tomato, spinach, and lettuce surfaces. The physicochemical surface properties of PDMS replicas and their natural counterparts, including roughness, topography, and hydrophobicity, and their effects on colloid retention were characterized and compared. The results demonstrated the feasibility of using PDMS replicas as surrogates of fresh produce for mechanistic studies of surface-bacteria interactions. Furthermore, the results highlighted that the surface properties of produce/replicas collectively control water retention and distribution on their surfaces, which were key factors in determining the amount and distribution of colloid retention. ☐ To further study colloid removal, the colloidal-contaminated surfaces were rinsed with different solutions, including DI water, NaCl solution, surfactants of SDS and Tween 80, and micro/nanobubble (MNBs) in combination with either water or surfactants. Colloid removal was largely controlled by the residual solution retention on the rinsed samples. The properties of rinsing solutions and the sample removal velocity were additional contributing factors to the amount and distribution of the retained residual solution. Colloid removal was also affected by the motion of the contact line, where the air-liquid interface contacts the colloid, which is related to the surface tension force acting on the colloid and the driven flows within the evaporating solution. These factors were, in turn, controlled by the properties of the sample surface and rinsing solution. Moreover, the results indicated that the MNBs could attach to the colloids, remove them from the sample surface efficiently, and then carry them to the solution surface. ☐ Overall, this work aims to gain significant insight into the mechanisms of pathogen retention on and removal from the complex surfaces of fresh produce. Such knowledge can contribute to the development of effective cleaning methods for various surfaces tainted with pathogens or other contaminants.University of Delaware, Department of Plant and Soil SciencesPh.D