Mechanisms of colloid removal from polydimethylsiloxane (PDMS) surfaces during washing: Implications for enhanced produce decontamination

Abstract

Microbial contamination of fresh produce poses significant challenges to food safety and public health. Postharvest washing is a common practice in the fresh produce industry to reduce microbial load. This study aimed to elucidate the mechanisms involved in bacterial removal from produce surfaces during washing, using model colloids as bacterial surrogates and polydimethylsiloxane (PDMS) replicas of tomato, lettuce, and spinach as model produce surfaces. Colloids were deposited onto the PDMS surfaces and subsequently washed using different solutions (DI water, NaCl, and surfactants Tween 80 and sodium dodecyl sulfate) at varying concentrations. The PDMS surfaces were then withdrawn from the solutions at two distinct velocities. Colloid removal efficacy and the associated physicochemical interactions between colloids and substrate surfaces under various washing conditions were quantified. The results revealed that colloid removal was controlled by the residual amount of washing solution retained and contact line action. These factors, in turn, were influenced by the sample-withdrawal velocity and physicochemical properties of substrate surfaces, colloids, and washing solutions. Specifically, SDS at 2 mol/m3 combined with a slow withdrawal velocity significantly optimized colloid removal, achieving up to 79.0% efficiency. Conversely, using Tween 80 at 0.08 mol/m3 concentration significantly impeded removal efficiency. Understanding these dynamics to minimize residual solution retention and optimize colloid/bacteria movement with the contact line upon washing can significantly enhance the cleaning efficacy of fresh produce. The findings of this study provide an improved understanding on the key factors governing the retention and removal of colloidal particles (including microorganisms) that can guide the development of effective decontamination strategies.