Effect of Surface Properties on Colloid Retention on Natural and Surrogate Produce Surfaces

Abstract

Bacterial contamination of fresh produce is a growing concern in food industry. Pathogenic bacteria can attach to and colonize the surfaces of fresh produce and cause disease outbreaks among consumers. Surface properties of both bacteria and produce affect bacterial contamination; however, the effects of produce roughness, topography, and hydrophobicity on bacterial retention are still poorly understood. In this work, we used spherical polystyrene colloids as bacterial surrogates to investigate colloid retention on and removal (by rinsing) from fresh produce surfaces including tomato, orange, apple, lettuce, spinach, and cantaloupe, and from surrogate produce surface Sharklet (a micro-patterned polymer). All investigated surfaces were characterized in terms of surface roughness and hydrophobicity (including contact angle and water retention area measurements). The results showed that there was no single parameter that dominated colloid retention on fresh produce, yet strong connection was found between colloid retention and water retention and distribution on all the surfaces investigated except apple. Rinsing was generally not efficient in removing colloids from produce surfaces, which suggests the need to modify current cleaning procedures and to develop novel contamination prevention strategies. This work offers a physicochemical approach to a food safety problem and improves understanding of mechanisms leading to produce contamination.

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

“…These results coincide with the colloid retention results shown in Figure , which suggests that the role of residual water retention in total colloid retention is paramount. The same correlation between residual water retention area and colloid retention was also observed in our previous study (Lazouskaya et al., ).…”

“…This is because the equilibrium contact angle is inadequate in describing wetting and air–liquid interface behavior on surfaces with heterogeneous topographic features. Nevertheless, results from the experiments with PDMS replicas further validated our previous conclusion (Lazouskaya et al., ) that produce surface hydrophobicity, topography, and roughness factors collectively controlled residual water retention and distribution, and consequently, the number of colloids retained.…”

“…Selected images of residual water retention area on the fresh produce and PDMS samples. Fresh produce images were reproduced from our previous study (Lazouskaya et al., ). For fresh produce, the water retention areas were measured with a fluorescence detection method and analyzed with Volocity software; for PDMS samples, the areas were measured with ImageJ software.…”

“…Surface topography and roughness were characterized using a confocal microscope (Zeiss 780, Carl Zeiss, Inc., Jena, Germany). Surface topography of the fresh produce and their replicas are complex and can only be characterized fully by defining multiple components including form, waviness, and roughness at various scales (Lazouskaya et al., ; Wang et al., ; Wennerberg & Albrektsson, ). Depending on the observation scale, the topography of a surface could be different (Wang et al., ).…”

“…Colloid retention. Colloid retention experiments followed similar procedures used in our previous study (Lazouskaya et al, 2016). Each PDMS sample surface (including the replicas and smooth control surfaces, 2 cm × 2 cm in area) was immersed into 15 mL colloid suspension (10 ppm) in a 50-mL disposable centrifuge tube, and shaken in a shaker (C76, New Brunswick Scientific Co., Inc., NJ, U.S.A.) for 1 hr at 0.28 g (140 rpm).…”