Dept. of Plant and Soil Sciences, Univ. of Delaware, 450 ISE Lab, 221 Academy Street, Newark, DE, 19716, U.S.A.
J Food Sci. 2019 Mar;84(3):524-531. doi: 10.1111/1750-3841.14479. Epub 2019 Feb 18.
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.
与新鲜农产品相关的食源性疾病在食品行业、科学界和公共卫生界引起了越来越多的关注。研究表明，新鲜农产品的表面特性会影响细菌的附着和定殖，但其中涉及的机制仍知之甚少。在我们之前的工作中，使用胶体作为细菌的替代品，我们证明了胶体在新鲜农产品上的保留受农产品表面上水的保留和分布的控制，而这又受农产品表面特性的控制。然而，由于天然样本之间的高度可变性和同时涉及的多个因素，使得解释结果和确定导致观察到的胶体保留行为的机制变得困难。为了更好地评估机制，本研究中使用聚二甲基硅氧烷（PDMS）复制了番茄、生菜和菠菜，并与新鲜农产品表面进行了比较。PDMS 复制品完全保留了其天然对应物的表面形貌特征，同时具有相同的化学性质（例如疏水性），因此可以分离表面形貌/粗糙度和疏水性的影响。我们发现，PDMS 复制品上的残留水保留和分布以及胶体保留与在相应的新鲜农产品表面上观察到的结果一致，但与天然表面相比，偏差较小。PDMS 复制品的使用提高了实验的可重复性，并能够区分表面疏水性和表面粗糙度对胶体保留的影响，从而能够更严格地阐明潜在机制。因此，PDMS 复制品可作为新鲜农产品的替代品，用于研究表面-细菌相互作用的机制。实际应用：这项工作证明了使用聚二甲基硅氧烷（PDMS）模拟新鲜农产品表面来研究农产品表面与胶体（包括细菌）之间相互作用的可行性。虽然使用水果或蔬菜表面更现实，但由于天然表面的异质性和可变性，使得系统和机制研究变得困难。使用 PDMS 复制品可以消除这些困难并提高实验的可重复性。本研究表明，PDMS 复制品可以充分代表天然农产品表面的形貌特征；胶体保留的结果为新鲜农产品污染和开发有效的消毒策略提供了深入的了解。
