Development of durable and superhydrophobic nanodiamond coating on aluminum surfaces for improved hygiene of food contact surfaces

Food packaging solutions in the post-per- and polyfluoroalkyl substances (PFAS) and microplastics era: A review of functions, materials, and bio-based alternatives

Food packaging (FP) is essential for preserving food quality, safety, and extending shelf-life. However, growing concerns about the environmental and health impacts of conventional packaging materials, particularly per- and polyfluoroalkyl substances (PFAS) and microplastics, are driving a major transformation in FP design. PFAS, synthetic compounds with dual hydro- and lipophobicity, have been widely employed in food packaging materials (FPMs) to impart desirable water and grease repellency. However, PFAS bioaccumulate in the human body and have been linked to multiple health effects, including immune system dysfunction, cancer, and developmental problems. The detection of microplastics in various FPMs has raised significant concerns regarding their potential migration into food and subsequent ingestion. This comprehensive review examines the current landscape of FPMs, their functions, and physicochemical properties to put into perspective why there is widespread use of PFAS and microplastics in FPMs. The review then addresses the challenges posed by PFAS and microplastics, emphasizing the urgent need for sustainable and bio-based alternatives. We highlight promising advancements in sustainable and renewable materials, including plant-derived polysaccharides, proteins, and waxes, as well as recycled and upcycled materials. The integration of these sustainable materials into active packaging systems is also examined, indicating innovations in oxygen scavengers, moisture absorbers, and antimicrobial packaging. The review concludes by identifying key research gaps and future directions, including the need for comprehensive life cycle assessments and strategies to improve scalability and cost-effectiveness. As the FP industry evolves, a holistic approach considering environmental impact, functionality, and consumer acceptance will be crucial in developing truly sustainable packaging solutions.

Bioinspired Superhydrophobic Nanocoating Based on Polydopamine and Nanodiamonds to Mitigate Bacterial Attachment to Polyvinyl Chloride Surfaces in Food Industry Environments

Polyvinyl chloride (PVC) is commonly utilized as a food-contact surface by the food industry for processing and storage purposes due to its durability, ease of fabrication, and cost-effectiveness. Herein, we report a composite coating for the superhydrophobization of PVC without the use of polyfluoroalkyl chemistry. This coating rendered the PVC superhydrophobic, exhibiting a static water contact angle of 151.9 ± 0.7° and a contact angle hysteresis of only 3.1 ± 1.0°. The structure of this composite coating, consisting of polydopamine, nanodiamonds, and an alkyl silane, was investigated by utilizing both scanning electron microscopy and atomic force microscopy. Surface chemistry was probed using attenuated total reflectance-Fourier transform infrared, and the surface wetting behavior was thoroughly characterized using both static and dynamic water contact angle measurements. It was demonstrated that the superhydrophobic PVC was cleanable using a food-grade surfactant, becoming wet in contact with high concentration surfactant solutions, but regaining its nonwetting property upon rinsing with water. It was demonstrated that the coating produced a 2.1 ± 0.1 log10 reduction (99.2%) in the number of Escherichia coli O157:H7 cells and a 2.2 ± 0.1 log10 reduction (99.3%) in the number of Salmonella enterica Typhimurium cells that were able to adsorb onto PVC surfaces over a 24 h period. The use of this fluorine-free superhydrophobic coating on PVC equipment, such as conveyor belts within food production facilities, may help to mitigate bacterial cross-contamination and curb the spread of foodborne illnesses.

Engineered Sustainable Omniphobic Coatings to Control Liquid Spreading on Food-Contact Materials

The adhesion of sticky liquid foods to a contacting surface can cause many technical challenges. The food manufacturing sector is confronted with many critical issues that can be overcome with long-lasting and highly nonwettable coatings. Nanoengineered biomimetic surfaces with distinct wettability and tunable interfaces have elicited increasing interest for their potential use in addressing a broad variety of scientific and technological applications, such as antifogging, anti-icing, antifouling, antiadhesion, and anticorrosion. Although a large number of nature-inspired surfaces have emerged, food-safe nonwetted surfaces are still in their infancy, and numerous structural design aspects remain unexplored. This Review summarizes the latest scientific research regarding the key principles, fabrication methods, and applications of three important categories of nonwettable surfaces: superhydrophobic, liquid-infused slippery, and re-entrant structured surfaces. The Review is particularly focused on new insights into the antiwetting mechanisms of these nanopatterned structures and discovering efficient platform methodologies to guide their rational design when in contact with food materials. A detailed description of the current opportunities, challenges, and future scale-up possibilities of these nanoengineered surfaces in the food industry is also provided.

Edible nano-encapsulated cinnamon essential oil hybrid wax coatings for enhancing apple safety against food borne pathogens

Post-harvest losses of fruits due to decay and concerns regarding microbial food safety are significant within the produce processing industry. Additionally, maintaining the quality of exported commodities to distant countries continues to pose a challenge. To address these issues, the application of bioactive compounds, such as essential oils, has gained recognition as a means to extend shelf life by acting as antimicrobials. Herein, we have undertaken an innovative approach by nano-encapsulating cinnamon-bark essential oil using whey protein concentrate and imbibing nano-encapsulates into food-grade wax commonly applied on produce surfaces. We have comprehensively examined the physical, chemical, and antimicrobial properties of this hybrid wax to evaluate its efficacy in combatting the various foodborne pathogens that frequently trouble producers and handlers in the post-harvest processing industry. The coatings as applied demonstrated a static contact angle of 85 ± 1.6°, and advancing and receding contact angles of 90 ± 1.1° and 53.0 ± 1.6°, respectively, resembling the wetting properties of natural waxes on apples. Nanoencapsulation significantly delayed the release of essential oil, increasing the half-life by 61 h compared to its unencapsulated counterparts. This delay correlated with statistically significant reductions (p = 0.05) in bacterial populations providing both immediate and delayed (up to 72 h) antibacterial effects as well as expanded fungal growth inhibition zones compared to existing wax technologies, demonstrating promising applicability for high-quality fruit storage and export. The utilization of this advanced produce wax coating technology offers considerable potential for bolstering food safety and providing enhanced protection against bacteria and fungi for produce commodities.

Durable superhydrophobic coatings for stainless-steel: An effective defense against Escherichia coli and Listeria fouling in the post-harvest environment

Increasing concerns revolve around bacterial cross-contamination of leafy green vegetables via food-contact surfaces. Given that stainless-steel is among the commonly used food-contact surfaces, this study reports a coating strategy enhancing its hygiene and microbiological safety through an antifouling approach via superhydrophobicity. The developed method involves growing a nickel-nanodiamond nanocomposite film on 304 stainless-steel via electroplating and sequential functionalization of the outer surface layer with nonpolar organosilane molecules via polydopamine moieties. The resultant superhydrophobic stainless-steel surfaces had a static water contact angle of 156.3 ± 1.9° with only 2.3 ± 0.5° contact angle hysteresis. Application of the coating to stainless-steel was demonstrated to yield 2.3 ± 0.6 log10 and 2.0 ± 0.9 log10 reductions in the number of adherent gram-negative Escherichia coli O157:H7 and gram-positive Listeria innocua cells, respectively. These population reductions were shown to be statistically significant (α = 0.05). Coated stainless-steel also resisted fouling when contacted with contaminated romaine lettuce leaves and maintained significant non-wetting character when abraded with sand or contacted with high concentration surfactant solutions. The incorporation of superhydrophobic stainless-steel surfaces into food processing equipment used for washing and packaging leafy green vegetables has the potential to mitigate the transmission of pathogenic bacteria within food production facilities.

Influence of surface properties on the adhesion of bacteria onto different casings

Bacteria adhere to the surfaces of sausage casing and form biofilms, which causes food spoilage and quality deterioration. However, bacterial adhesion to the casing surfaces has not received enough attention and has not been extensively studied. In this study, the effect of the physicochemical properties of casing surfaces on bacterial initial adhesion were investigated with Leuconostoc mesenteroides as model bacteria. The adhesion of Leuconostoc mesenteroides onto 5 types of casings were systematically investigated, including animal casings, collagen casings, cellulose casings, fiber casings, and nylon casings, which are the most frequently encountered casings in sausage processing. It was found that the number of viable cells on the casings following the trend as: animal casings > collagen casings > fiber casings > cellulose casings > nylon casings after 4 h of incubation time. This phenomenon might be due to the different physicochemical properties of the different casings. Therefore, physicochemical factors, including zeta potential, hydrophobicity and roughness of casings, zeta potential and hydrophobicity of Leuconostoc mesenteroides, were further characterized. In terms of hydrophobic interactions, the results showed that the number of bacteria attached to the casings did not conform to the trend of hydrophobic interaction. In terms of electrostatic interactions, the results showed that the number of bacteria attached to the casings did not conform to the trend of hydrophobic interaction. The casings with different surface roughnesses in a range of 1.67-20.83 μm, the variation of bacterial adhesion quantity was in good agreement with the variation trend of casing roughness, the result showed that the surface roughness was the key factor dominating the bacterial adhesion rate compared with the surface hydrophobicity and zeta potential. The results give new insights to explore the mechanism of bacterial adhesion on casings and prevent sausage spoilage.

Fabrication and Characterization of Superhydrophobic Al-Based Surface Used for Finned-Tube Heat Exchangers

Enhancing the heat transfer performance of heat exchangers is one of the main methods to reduce energy consumption and carbon emissions in heating, ventilation, air-conditioning and refrigeration (HVAC&R) systems. Wettability modified surfaces developed gradually may help. This study aims to improve the performance of heat exchangers from the perspective of component materials. The facile and cost-effective fabrication method of superhydrophobic Al-based finned-tube heat exchangers with acid etching and stearic acid self-assembly was proposed and optimized in this study, so that the modified Al fins could achieve stronger wettability and durability. The effect of process parameters on the wettability of the Al fins was by response surface methodology (RSM) and variance analysis. Then, the modified fins were characterized by field-emission scanning electron microscopy (FE-SEM), 3D topography profiler, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR), respectively. The durability of the superhydrophobic fins was investigated by air exposure, corrosion resistance, and mechanical robustness experiments. The RSM and variance analysis demonstrated that a water contact angle (WCA) of 166.9° can be obtained with the etching time in 2 mol/L HCl solution of 10.5 min, the self-assembly time in the stearic acid ethanol solution of 48 h, and drying under 73.0 °C. The surface morphology showed suitable micro-nano structures with a mean roughness (Ra) of 467.58 nm and a maximum peak-to-valley vertical distance (Rt) of 4.095 μm. The chemical component demonstrated the self-assembly of an alkyl chain. The WCAs declined slightly in durability experiments, which showed the feasibility of the superhydrophobic heat exchangers under actual conditions.

Effect of Protein Adsorption on Air Plastron Behavior of a Superhydrophobic Surface

Protein fouling on critical biointerfaces causes significant public health and clinical ramifications. Multiple strategies, including superhydrophobic (SHP) surfaces and coatings, have been explored to mitigate protein adsorption on solid surfaces. SHP materials with underwater air plastron (AP) layers hold great promise by physically reducing the contact area between a substrate and protein molecules. However, sustaining AP stability or lifetime is crucial in determining the durability and long-term applications of SHP materials. This work investigated the effect of protein on the AP stability using model SHP substrates, which were prepared from a mixture of silica nanoparticles and epoxy. The AP stability was determined using a submersion test with real-time visualization. The results showed that AP stability was significantly weakened by protein solutions compared to water, which could be attributed to the surface tension of protein solutions and protein adsorption on SHP substrates. The results were further examined to reveal the correlation between protein fouling and accelerated AP dissipation on SHP materials by confocal fluorescent imaging, surface energy measurement, and surface robustness modeling of the Cassie-Baxter to Wenzel transition. The study reveals fundamental protein adsorption mechanisms on SHP materials, which could guide future SHP material design to better mitigate protein fouling on critical biointerfaces.

Recent developments in antimicrobial and antifouling coatings to reduce or prevent contamination and cross-contamination of food contact surfaces by bacteria

Illness as the result of ingesting bacterially contaminated foodstuffs represents a significant annual loss of human quality of life and economic impact globally. Significant research investment has recently been made in developing new materials that can be used to construct food contacting tools and surfaces that might minimize the risk of cross-contamination of bacteria from one food item to another. This is done to mitigate the spread of bacterial contamination and resultant foodborne illness. Internet-based literature search tools such as Web of Science, Google Scholar, and Scopus were utilized to investigate publishing trends within the last 10 years related to the development of antimicrobial and antifouling surfaces with potential use in food processing applications. Technologies investigated were categorized into four major groups: antimicrobial agent-releasing coatings, contact-based antimicrobial coatings, superhydrophobic antifouling coatings, and repulsion-based antifouling coatings. The advantages for each group and technical challenges remaining before wide-scale implementation were compared. A diverse array of emerging antimicrobial and antifouling technologies were identified, designed to suit a wide range of food contact applications. Although each poses distinct and promising advantages, significant further research investment will likely be required to reliably produce effective materials economically and safely enough to equip large-scale operations such as farms, food processing facilities, and kitchens.