Polydimethylsiloxane Replicas Efficacy for Simulating Fresh Produce Surfaces and Application in Mechanistic Study of Colloid Retention.

Foodborne illnesses associated with fresh produce have attracted increasing attention in the food industry, scientific and public health communities. Studies have shown that surface properties of fresh produce can affect bacterial attachment and colonization, yet the mechanisms involved remain poorly understood. In our previous work, using colloids as bacterial surrogates, we demonstrated that colloid retention on fresh produce was controlled by water retention/distribution on produce surfaces, which were in turn governed by produce surface properties. However, high variabilities among the natural samples and multiple factors that were simultaneously involved made it difficult for interpreting the results and in pinpointing the mechanisms responsible for the observed colloid retention behavior. To better evaluate the mechanisms, polydimethylsiloxane (PDMS) replicas of tomato, lettuce, and spinach were fabricated and compared with fresh produce surfaces in this study. The PDMS replicas thoroughly preserved the surface topographical features of their natural counterparts while having identical chemical properties (for example, hydrophobicity), thus, allowing for the separation of surface topography/roughness and hydrophobicity effects. We found that residual water retention/distribution and colloid retention on the PDMS replicas were consistent with the results observed on the corresponding fresh produce surfaces, but had smaller deviations from the respective means when compared to the natural surfaces. The use of PDMS replicas improved experimental reproducibility, and enabled differentiation on the effects of surface hydrophobicity and surface roughness on colloid retention, thus, allowed more rigorous elucidation of the underlying mechanisms. Therefore, PDMS replicas could be used as surrogates of fresh produce for mechanistic studies of surface-bacteria interactions. PRACTICAL APPLICATION: This work demonstrates the feasibility of using polydimethylsiloxane (PDMS) to simulate fresh produce surfaces for studying interactions between produce surfaces and colloids, including bacteria. Although it is more realistic to use fruit or vegetable surfaces, the difficulties of working with natural surfaces that are heterogeneous and variable hinder systematic and mechanistic studies. The use of PDMS replicas can eliminate these difficulties and improve experimental reproducibility. This study demonstrated that PDMS replicas could adequately represent the topographical features of natural produce surfaces; the results on colloid retention provided insight into fresh produce contamination and the development of effective decontamination strategies.