ARROW@TU Dublin ARROW@TU Dublin Advances in emerging technologies for the decontamination of Advances in emerging technologies for the decontamination of the food contact surfaces the food contact surfaces

Foodborne pathogens could be transferred to food from food contact surfaces contaminated by poor hygiene or biofilm formation. The food processing industry has various conditions favouring microbes ’ adherence, such as moisture, nutrients, and the microbial inoculums obtained from the raw material. The function of the ideal antimicrobial surface is preventing initial attachment of the microbes, killing the microbes or/and removing the dead bacteria. This review article provides detail about the challenges food industries are facing with respect to food contact materials. It also summarises the merits and demerits of several sanitizing methods developed for industrial use. Furthermore, it reviews the new and emerging techniques that enhance the efficiency of reducing microbial contamination. Techniques such as surface functionalisation, high-intensity ultrasound, cold plasma technologies etc. which have high potential to be used for the decontamination of food contact surfaces are discussed. The emerging designs of antibacterial surfaces provide the opportunity to reduce or eradicate the adhesion of microorganisms. The most important purpose of these surfaces is to prevent the attachment of bacteria and to kill the bacteria that come in contact. These emerging technologies have a high potential for developing safe and inert food contact materials for the food industry.


Introduction
Pathogenic microorganisms can be transferred to food through contact with a contaminated surface. Biofilms are generally composed of single or multiple species, forming multi-species biofilms, which have higher antimicrobial resistance and may contain spoiling and pathogenic bacteria (Galie et al., 2018). The characteristics of the involved bacteria (i.e., cell surface appendages, surface charge strain, metabolic activity), the attachment surface (material, wettability, roughness etc.) and the surrounding environment (pH, temperature etc.) all play a role in biofilm formation (Pagán and García-Gonzalo, 2015). In many studies, it was also observed that the biofilm pathogens were resistant to the anti-microbial agent, indicating that the food contact surface was not reacting against the microbes and needed to change its coating agent (Refaat, 2011;Pagán and García-Gonzalo, 2015;Rossi et al, 2020). To assure the quality and safety of food, the quality assurance systems enable the verification and application of control measures.
The way to limit the spread of these microorganisms is to restrict their survival on contact surfaces. However, the emerging designs of antibacterial surfaces provide the opportunity to reduce or eradicate the adhesion of microorganisms. The major purpose of these modified food contact surfaces (FCS) is to prevent microorganism attachment or eradication. The surface modification could be done via variable approaches like adsorption, covalent binding or surface topography modification. Several antimicrobial agents have been used to alter the properties of the surface, such as enzymes (Weerarathne et al., 2020), peptides (Hosseini et al., 2019), essential oils  and polymers (Perera et al., 2021).
The development of the modified surface was done either utilizing the coating or by modifying the topography of the surface, and very few studies have focused on contamination through food contact surfaces. Such coatings mainly involve highly hydrated polymers like poly (ethylene glycol) (PEG), which have a high-water affinity and high entropy, leading to the exhibition of antifouling property. Polycationic peptides such as chitosan have been studied and proved as an efficient antibacterial agent as their positively charged cationic chain effectively disrupts the negatively charged walls of the bacteria. Schaer et al. (2012) demonstrated that the polycation-based surface coated with N-alkylpolyethyleneimine or poly (N-alkyl-pyridinium) effectively kills a broad spectrum of bacteria. Srivastava and Kotov (2008) developed a costeffective versatile technique for the layer-by-layer formation of a multilayer coating. These multilayer coatings have multifunctional properties such as antibiofilm, antibacterial, and antiadhesive activity. The antiadhesive property of the coatings was due to the incorporation of the hydrophilic polymer, and the polycationic content in the coating led to the antibacterial activity.
The present review article aims at providing a comprehensive overview of challenges the food industry is facing with respect to food contact materials. The article also summarises several cleaning methods developed for industrial use and their merits and drawbacks. It also discusses new and emerging techniques such as natural active agents, surface functionalisation, cold plasma technique etc. which have high potential to be used for the decontamination of food contact surfaces.

Challenges of the food industry with respect to food contact materials
Various conditions in the food processing industry, such as the availability of nutrients, moisture content, and microbial inoculum derived from the raw material, favour the adherence of microorganisms on the food contact surface. Biofilms are developed on the surfaces, escalating the complex ecosystem and causing contamination (Gutiérrez et al., 2016). Recent research discovered that the viable L. monocytogenes biofilm remained even after cleaning and disinfectant application (Gião and Keevil, 2014;Overney et al., 2017). Bio-deterioration is also considered as a major challenge for the food industry as all food will deteriorate to some extent once it is slaughtered or harvested. Any undesirable change in the property of a material because of a microorganism is known as bio-deterioration. The deterioration of food could be the loss of its nutritional value, change in colour and becoming vulnerable.
One of the concerns for the management of microbiological food safety issues is to implement effective controls without increasing prices unnecessarily or compromising taste and nutritional value (Havelaar et al., 2010). As a result, microbial risk management necessitates a detailed awareness of the entire food supply chain. Screening the microbial load in the final product is often ineffective in terms of hazard control, as it is impossible to test enough samples to provide the statistical power required to identify pollutants at levels that pose unacceptable health hazards (Havelaar et al., 2010).
Raw material, such as raw meats, fish and poultry, may contain pathogenic bacteria. During storage or food preparation, pathogenic bacteria could be transmitted to other food materials, such as cooked or ready-to-eat foods. Various studies suggested the contamination of microbes such as L. monocytogenes, S. aureus, E. coli, etc. in food from the food contact surface (Colagiorgi et al., 2017;Møretrø and Langsrud, 2017;Ripolles-Avila et al., 2019). Contamination could also occur between the allergens and the allergen-free food commodities. Formation and dispersal of the biofilm are affected by various factors such as the surface material and its properties, specific bacterial strain (Borucki et al., 2003;Chae and Schraft, 2000), temperature (Donlan & Costerton, 2002), pH, and nutrient content. A proactive strategy is necessary, beginning with the manufacturer assuring a safe process and product design, as well as anticipating potential problems instead of detecting them after they have developed (Havelaar et al., 2010).

Microorganism transfer from food contact materials
It is a well-known fact that a high percentage of foodborne illnesses are caused by a failure to maintain hygiene during food preparation. A common practice that is the major cause of the contamination is the use of the same kitchen equipment for both raw material and ready-to-eat foods. It may lead to the contamination of fresh fruits and vegetables by the pathogenic microorganisms from the raw meat, which does not go through any thermal processing before consumption.
The consequence of contaminated surfaces as a mode of pathogen transfer to food is very common in domestic settings. However, according to a survey by Gkana, Lianou, and Nychas carried out in 2016, the majority of people realise the importance of cleaning and maintaining the hygiene of the food contact surfaces while preparing ready to eat food. A significant number of consumers also admit to being victims of poor food handling practices (Ehuwa et al., 2021;, Myintzaw et al., 2021). These inappropriate practices include the use of inefficient washed or unwashed cutting boards during food preparation, as well as the reuse of the same surfaces for handling both raw meat and ready-toeat foods (Gkana, Chorianopoulos, et al., 2017;Gkana, Doulgeraki, et al., 2017).
The physicochemical properties of the food contact surface are modified to avoid the accumulation or attachment of the food particles on the surface, which could support microbial growth by providing them with nutrients. Some studies have evaluated the contamination of pathogens between cutting boards and meat. The studies which relate the effect of the surface material on microbial transfer mainly concentrate on stainless steel and polyethylene, as the majority of the food processing equipment is made of them (Cappitelli et al., 2014;Di Ciccio et al., 2015;Hamadi et al., 2014). In quantitative microbial risk assessment, the source, occurrence, and level of contamination are under consideration. Several studies have also reported that the microorganism could survive on the food contact material for hours and days (Gkana, Doulgeraki, et al., 2017). However, the risk of foodborne illness associated with contamination is not only dependent on the surface contamination, but also on the probability of transfer to other surfaces. Therefore, several studies include the examinination of different factors for the migration of bacteria from meat to contact surfaces and from surface to meat (Fagerlund et al., 2017;Giaouris et al., 2014;Lo et al., 2019). The surface ringing with tap water does not help to reduce the bacterial loads to safe levels. However, some studies revealed that the mechanical washing of surfaces, especially polyethylene and stainlesssteel with detergent and water, is capable of reducing contamination between raw meat and fresh produce significantly (Gkana, Chorianopoulos, et al., 2017;Gkana, Doulgeraki, et al., 2017).
On the other hand, neither the spray disinfectant application nor mechanical washing with detergent and water are adequate to entirely avoid contamination and hence protect consumers from foodborne infections. Therefore, due to the absence of sufficient cleaning and disinfection procedures, the approach to prevent contamination is the use of different kitchen equipment for the preparation and handling of raw meat and fresh produce is inadequate (Gkana, Chorianopoulos, et al., 2017;Gkana, Doulgeraki, et al., 2017).

Existing solutions and their drawbacks
Planktonic cells of the same species are far more resistant to biocidal chemicals than bacteria that live in biofilms on surfaces. As a result, regular sanitation and disinfection treatments may fail to prevent contamination in some environments. To sanitize the material surface, it must be disinfected and cleaned effectively. Most commonly used, Clean-in-place (CIP) systems use rinse cycles and aqueous cleaning solutions to deactivate bacteria on equipment surfaces in commercial food processing plants. Clostridium perfringens attached to stainless steel, for example, was deactivated utilizing several CIP regimes that included the use of sodium hydroxide (NaOH) as an active cleaning agent. However, studies found CIP systems are sometimes not effective (Alzubeidi et al., 2018;Torres Dominguez et al., 2019). Khamisse et al. (2012) observed that the Ricotta facility's industrial cleaning and disinfection system did not substantially reduce total cell counts from stainless steel and PVC surfaces, despite the surfaces appearing clean after the cleaning procedure. In the food industry, many sanitizing processes are utilized such as radiation, heat, and chemicals. Electrolytic solutions' efficiency, strong bases or acids' effectiveness, and the effects of detergent concentration, water temperature, and surface material have been studied extensively (Torres Dominguez et al., 2019). Because of the high expense, radiation is used less frequently than heat and chemical treatment. Various chemicals, such as iodine and chlorine, react with food and dirt on the surface, becoming less effective and failing to disinfecting it properly (Table 1). Heat can be used to sanitize surfaces in three ways: hot air, steam, and hot water. As the temperature of the water in hot water treatment is around 75 ℃, it has the disadvantage of having limited efficacy and requiring a large amount of water. Similarly, steam has an effect on the surface's moisture and heat-sensitive areas, as well as causing oxidation. For the treatment with hot air, the surface material is heated to 82 • C for 20 min, which could also deteriorate the material.
Technologies such as steam spray, hot water and brushing are used in the food industry to maintain good hygiene practices. In these technologies, there is an indirect delivery of the physical energy and requires direct contact with the contaminated surface for effective decontamination. The boilers or pump provide steam spray in the spray system; the liquid is pressurized and sent to a nozzle, which increases the velocity of the steam and directs it towards the surface (Marriott and Gravani, 2006). To clean the surface, a high-velocity of steam is sprayed on it. Sprays are only effective on surfaces to which they have direct access; they are unable to reach hidden areas. Yang et al. (2017) studied the effect of hot water sanitation on egg processing. They performed the  (Møretrø et al., 2012;Weber and Rutala, 2013) treatment at 71 • C for the 30 s and observed the reduction of S. enteritidis biofilms by 4.3-7.08 log CFU/cm 2 . Also, they had observed that the hot water treatment was more efficient at removing the S. enteritidis biofilms than chlorine (Yang et al., 2017). However, various studies have observed no effect of heat on the microbes due to resistance (Bae et al., 2009;Kim et al., 2017;Rico-Munoz, 2017). However, brushing has limited efficacy in terms of the approachable area for the bristles of the brush. The surface where bristles are unable to reach will not be cleaned (Fuchs, 2015). The antimicrobial efficacy of chemicals is mainly influenced by three factors: concentration, temperature and contact time. The concentration of the chemical agent must be optimised thoroughly as less concentration will reduce harmful microorganisms inadequately and too much concentration could be toxic. Chemical sanitisers are said to work best between 13 • C and 49 • C in water. The recommended length of contact time must be maintained in order to kill the microorganism effectively. Chlorine, iodine, hydrogen peroxide and quaternary ammonium are the approved chemicals used as a sanitiser. In bacteria, hydrogen peroxide causes the release of reactive oxygen species, which causes the oxidation of the cytoplasmic content or cell wall disintegration ( Fig. 1) Chlorine is broadly used in the food industry due to its costeffectiveness, and its ability to act as a broad-spectrum antimicrobial agent (Ramos et al., 2013). But it has also been observed that chorine tends to be more corrosive and irritating than quaternary ammonium compounds or iodine compounds (Marriott and Gravani, 2006). Chlorine dioxide reacts with the cellular enzymes in the bacteria (Fig. 1).
Chlorine dioxide (ClO 2 ) of 200 μg/mL reduces 4.42 log CFU/mL of B. cereus on stainless steel surfaces (Kreske et al., 2006). Poimenidou et al. (2016), observed that the L. monocytogenes biofilms formed on stainless steel surfaces were more resistant to disinfectants than those formed on polystyrene (Poimenidou et al., 2016). Significant quaternary ammonium tolerance was found in the persistent strain of the greatest producer of biofilm. Also, a positive correlation was found between the biofilm formation on the stainless steel and quaternary ammonium tolerance (Poimenidou et al., 2016). However, conventional solutions are only effective for a limited time and have a lot of disadvantages, motivating the development of new technology to protect food contact materials from microorganisms. Recent studies have concentrated on combining less toxic sanitizing solutions and determining the influence of surface qualities and food product components on the efficiency of mechanical-chemical procedures.

Natural antimicrobial surface coating
Naturally derived antimicrobial agents can be obtained from various sources, such as animals, plants, bacteria, fungi, and algae. Numerous studies have confirmed the efficiency of plant-derived compounds and efficacy-influencing factors (Gyawali & Ibrahim, 2012;Hayek et al., 2013) (Table 2). Many unexplored potential sources could be used in the food industry; for example, polyphenols are the secondary metabolites of plants. They play a very important role in the defense against plant pathogens and all adverse conditions like high rainfall, UV radiation and many more. With respect to their chemical structures, a wide range of polyphenols could be divided into two subcategories: flavonoids and non-flavonoids. More than 4000 flavonoids have been derived from many plants like vegetables, fruits and beverages (Chahar et al., 2011).
Depending on the oxidation state of the central pyran ring, the flavonoids are further divided into many subcategories such as flavonols, flavones, flavanones, anthocyanidins, flavonols, and isoflavones. Nonflavonoids, depending upon the first phenolic acid, could be subdivided into derivatives of benzoic acid (gallic acid, protocatechuic acid), derivatives of cinnamic acids (ferulic, coumaric and caffeic acid), and second stilbenes (resveratrol, in both cis and trans isomeric forms) and lignans (oxidative dimerization of two phenylpropane units). Colon and Nerín (2016) summarize that the total antioxidant capacity of green tea extract was affected by synergistic, antagonistic, and additive interactions among green tea polyphenols. In addition, catechins were found to be responsible for synergism in green tea extract, with gallocatechin gallate (GCG), epigallocatechin gallate (EGCG), catechin gallate (CG), and epicatechin gallate (ECG) accounting for the majority of synergistic interactions (Colon & Nerín, 2016). Moreover, Picchio et al., (2018) observed that tannic acid was an efficient crosslinking agent for casein protein and that the resulting films, which have enhanced physicochemical properties, can be used for food packaging. Sharma et al. (2020) incorporated ferulic acid into a poly (lactide) -poly  (butylene adipate-co-terephthalate) (PLA-PBAT) polymer blend and observed enhancement in mechanical properties, UV barrier properties, thermal degradation, and antimicrobial activity. The presence of the phenolic component in the composite film has been shown to improve antibacterial activity against Listeria monocytogenes and E. coli (Sharma et al., 2020). Dos Santos Rodrigues et al. (2017), have studied the effects of oregano essential oil and carvacrol on biofilms of Staphylococcus aureus from food-contact surfaces. The results showed a significant prevalence of biofilm producers S. aureus isolated from food-contact surfaces, as well as the effectiveness of oregano and carvacrol in inhibiting planktonic and sessile cells. Because of the potential for inductive biofilm development, the concentrations of these antimicrobials employed to inhibit S. aureus biofilms should be carefully considered (Dos Santos Rodrigues et al. 2017). Soni et al. (2013) discovered that exposure to Carvacrol (0.05 to 0.1%) for 1 h on polystyrene and stainless-steel surfaces reduced Salmonella spp. growth by 7 log CFU/ml (Soni et al., 2013). Wang et al. (2017) demonstrated the potential of tannic acidincorporated soy protein isolate-based nanocomposite films for food packaging applications, demonstrating effective UV barrier properties and hydrophobicity (Wang et al., 2017). Sharma et al. (2020) have also studied the incorporation of clove oil and thyme oil into poly (lactide)poly (butylene adipate-co-terephthalate) (PLA-PBAT) for food packaging applications. The authors observed that the clove oil composite film exhibited UV blocking properties and strong antimicrobial activity (6.5 log reduction of S. aureus) (Sharma et al., 2020a).

Dual-functional surface coating
An ideal antimicrobial surface must prevent the initial attachment of microorganisms, kill the microbes, or remove the dead microorganisms. Various studies have resulted in the development of surfaces that combine two strategies in one system, resulting in the development of three types of dual-functional antimicrobial surfaces that can kill and resist, resist and release, and kill and release microorganisms.
Dual functional coatings are antimicrobial surfaces based on the combination of bactericidal and microorganism resistant properties. These surfaces could either have a spacer/non-biofouling agent such as hydrophilic polymer or have a deposition of an antiadhesive layer or the substantial release of an antimicrobial agent embedded in a non-fouling matrix. Ahmadi and Ahmad (2019) have developed a sustainable, active dual-functional (antimicrobial/anticorrosive) polyurethane nanocomposite (PUC) coating using the synergistic activity of π-π interaction and in situ graphene oxide integration. The coated surfaces had shown prolonged anticorrosive activity in NaCl (5%) solution and reduced bacterial surface colonization against S. typhimurium by 6.5 and L. innocua   (Demir et al., 2017) Silica nanoparticles Aluminium Attachment of Salmonella typhimurium LT2 and Listeria innocua was reduced>99.0% (Oh et al., 2019) Sol-gel-based Stainless Steel Reduction in the amount of fouled layer on modified surfaces (Liu, Jindal, et al., 2017;Liu, Wu, et al., 2017) (Dong et al., 2017) Cold nitrogen plasma with essential oil Stainless steel, glass sheet and polystyrene plastic S. aureus biofilm was approximately reduced by 2 logs after individual treatment (Cui et al., 2016) sintered silica nanoparticles. An exceptionally high log reduction of 6.5 log CFU/ml for Salmonella typhimurium LT2 and 4 log CFU/ml for L. innocua were observed as compared to the control (bare aluminium surface) . Nanoparticles appeared to give improved stability, efficacy, and cost-effectiveness. Other kill and resist methods include layer by layer deposition of antimicrobial and non-fouling layers and release of antimicrobial agents from the non-fouling matrix. The layer by layer is the cost-effective technique in which multi-layers are utilized as a reserve for the loading and release of antimicrobial agents. Oh et al. (2015) evaluated the potential of hydrophobically enhanced, silica aerogel as antiadhesion food contact surfaces and observed bacterial antiadhesion property. Also, the novel food contact surface showed superior thermal insulation and ultra-lightweight properties (Oh et al., 2015). In addition, Yang et al. (2012) studied a composite system of a multilayer film of PVA/PAA and chitosan/heparin. Furthermore, the controlled release of anti-microbial agents from the surface reduces microorganism colonisation and inhibits their propagation. Various zwitter-ionic hydrogels with a controlled release anti-microbial agent have been developed to attain antimicrobial property and non-fouling of the surface.
Kill and release is the combination of bactericidal and microorganisms release properties in a system. Accumulation of dead microorganisms on the surface effectively degrades the bactericidal property of the surface, also serving as a nutrient source for other microorganisms (Mi & Jiang, 2014). Therefore, there is a need to release or remove the debris of dead microorganisms to maintain antimicrobial properties for the longer term. Fan et al. (2014) modified the surface by attaching a cationic precursor carrying a quaternary amine group, which has the property of killing the microorganism attached to the surface initially. The cationic ester group hydrolysis in the basic or neutral aqueous environment leads to the transition of a zwitter ionic surface that releases the debris of dead microorganisms to maintain the non-fouling property (Cheng et al., 2008;Mi & Jiang, 2014). Gautam et al. (2021), modified cellulose papers to have antibacterial qualities that kill and release in a hybrid approach. Using the SI-ATRP method, cellulose papers are first grafted with the thermoresponsive copolymer poly (Nisopropylacrylamide-co-2-aminoethyl methacrylate) (p(NIPAAm-co-AEMA)). Electrostatic interactions between positively charged AEMA copolymer and negatively charged AgNPs are then used to immobilize antibacterial silver nanoparticles (AgNPs) onto the surfaces. The study validates the efficient killing of E. coli and the release of over 90% of the dead bacteria with a single thermo-responsive wash (Gautam et al., 2021).

Surface functionalisation
The development of different methods for the modification of surfaces has led to an improvement in the safety and inertness of the food contact materials. The use of wet chemicals, UV radiation, and adhesion are used to add a variety of polar groups to the surface. Therefore, these techniques must add a specific functional group to the surface. The first step for the surface modification is the selection of the polymer-based on properties like elasticity, conductivity, strength, type of material (synthetic or natural) and degradability. Immobilisation of biomolecules or the functionalisation of surfaces is considered according to the application of the surface. Therefore, the second step is to enhance the functionalisation techniques of the surface to add the desired quantity and variety of the reactive functional group. Grafting of the polyfunctional agent on the surface increases the availability of the reactive functional groups per unit area. The addition of a spacer molecule for harnessing the bioactive compound on a solid surface also increases bioactivity. It reduces the steric hindrance and covers the compound with a hydrophobic surface. The final step is the covalent attachment of the natural or synthetic bioactive compound to the functionalised polymer surface.
The surface modification is done either by atom radical transfer or by covalent bonding. Some antibacterial property was carried out on the surfaces which have chemically bonded hydrophobic polycations of a quaternary ammonium salt. The physicochemical characteristics, cytotoxicity, and antibacterial activity of quaternary ammonium amino acidbased surfactants are greatly influenced by the length of the hydrocarbon chain and are unaltered by the polar head of the amino acid (leucine or methionine) (Perinelli et al., 2019). In addition, nylon, poly (ethylene terephthalate), polyethylene, polypropylene have shown antibacterial effects. Alkylated PVP and benzyl PVP are polyvinyl pyridine-based polymers which are phosphonium or sulphonium or the polycationic quaternary ammonium salts. The antimicrobial property of these polymers depends on the length of the chain. Polymers with oxidative halogen group (Cl + , Br + ) are the polymeric compounds with the Nhalamine group which exhibit antibacterial property. The compounds having amphiphilic quaternary dimethyl ammonium compounds having oxyethylene and n-alkyl groups are synthesized and designed as surfaces that have self-decontaminating properties (Harney et al., 2008). Shao et al. (2017) produced an A-g-BC film by alkoxysilane polycondensation using (3-aminopropyl) triethoxysilane. This A-g-BC membrane exhibited efficient antibacterial and antifungal activities against S. aureus, E. coli, C. albicans and S. subtilis . Zhang and Han (2019), had immobilized poly-N,N ′ -[(4,5-dihydroxy-1,2-phenylene)bis(methylene)] bisacrylamide (POHABA) onto the surface of PE cling film through precipitation polymerization and UV polymerization. Because of the higher surface distribution of OHABA, antibacterial PE cling films made by precipitation polymerization were found to have better antibacterial activity than those made by UV polymerization (Zhang & Han, 2019). In addition, the potential fast and energy-saving approach is the use of high-intensity ultrasound. An ultrasonic approach to form a hybrid functional surface is based on the cavitation effect on the solid surfaces . The surfaces modified ultrasonically have microcavities in them of a nano-meter thickness in which different chemicals such as antimicrobial agents could be stored . The interfaces of ultrasonically modified surfaces are very rough; therefore, they provide excellent adhesion for inorganic and organic coatings. The development of industrial applications for the modification and functionalisation of solid surfaces by ultrasonic irradiation is focused of study for many researchers.

Modification of surface topography
The propensity of bacteria for adhesion and colonisation on the surface of material leads to the formation of biofilm which may result in the contamination of the food and its product. However, only a few studies were carried out to find out the effect of the topography of the surface on the interaction between the material and the bacteria. Hsiao et al. (2014) had adsorbed copolymers of poly (propylene oxide) and poly (sulfobetaine methacrylate) on three kinds of surface topographies (indented, smooth and convex). They found the convex and smooth surface exhibited better resistance to the attachment of bacterial cells. The differential orientation of the copolymers resulted in the coverage of the surface by the zwitter ionic molecule more efficiently. In addition, the indented surface exhibited better anti-biofouling ability than the curved surface as the bacterial cells were unable to adhere between the indents (Hasan & Chatterjee, 2015). Awad et al. (2018), had studied food-safe oil-based slippery coatings (FOSCs) that prevent bacterial adhesion and biofilm formation by encapsulating residual oil lubricant within surface holes, preventing microbial growth. They used alkylphosphonic acid to functionalize the stainless-steel surface to get a coating of food-grade oil. Their findings suggest the potential of lowcost, sustainable techniques to improve the cleanability of SS foodprocessing surfaces and improve food safety by minimizing biofilm formation (Awad et al., 2018). Rajab et al. (2017), had evaluated the impact of laser-created titanium surfaces with progressive topographical characteristics on bacterial adhesion and persistence. They observed under static inoculation settings, the combination of surface chemistry, topography, and physiochemistry resulted in a stronger anti-adhesive surface (Rajab et al., 2017). Demir et al. (2017) designed a modified stainless steel surfaces with an N-halamine-based copolymer to induce antimicrobial activity. In 15 min of contact time, the modified stainless-steel surface deactivated S. aureus and E. coli O157: H7 bacteria by 6 logs (Demir et al., 2017). The roughness of the surface determines the interaction of the surface with its environment. Generally, rough surfaces are undesirable as they are difficult to clean as compared to smooth surfaces. The R a value is commonly used to determine the roughness of a surface. R a can be defined as the arithmetic mean of the vertical deviation of the filtered roughness profile. A typical R a value for a hygienic surface is 0.8 μm. As the R a value is an arithmetical measure, it does not convey the actual attribute size or the variation in the size of the attribute along the surface. A new possibility of designing a more hygienic surface depends on the use of the intended environment by surface fabrication with nanotopographies (Kim et al., 2013;Meng et al., 2016).
An increase in the surface area of antimicrobial surfaces that release antimicrobial agents could improve their efficacy. However, the presence of previous organic substances such as food, blood or a microorganism could obstruct the antimicrobial effect. Attributes such as profile, size, and shape increase the cell contact area and enhance their ability to retain. Also, it is important to consider the issue of inactivation and cell survival. Therefore, it is necessary to consider all these subjects while developing an effective and novel hygiene surface. Studies revealed that on the titanium-coated stainless steels the removal of microorganisms was easier along with the attribute while, for the soft polymeric surface, the removal was easier by applying force across the attribute (Verran et al., 2014(Verran et al., , 2010. This has led to surface fabrication with intended topographies which inhibit the initial microbial attachment and enhance hygiene.

High-intensity ultrasound
The application of ultrasound has gained significant attention in the food industry in recent years. In the food sector, ultrasound is regarded as a green and cost-effective technology (Zheng et al., 2019). Sound waves of high intensity and high frequency in a liquid are used to enhance the decontamination of the surfaces immersed in an ultrasonically activated liquid. Recently, ultrasound has become more popular and has developed numerous applications with chemical processes and conditioning of surfaces. This is non-destructive technology and has several advantages, such as uniform cleaning, microbial safety, and assurance of food quality. However, further research should be carried out to make the technology cost-effective for industrial use (Arvanitoyannis et al., 2017).
Ultrasonic cleaning is a unique and highly efficient technology. With the sound conducting liquid as the medium, it can infiltrate and clean any surface. It is also competent at cleaning complex tasks like blind holes, minute surface contours, tread roots and many more. In the compression cycle, positive pressure can bring molecules together; in the expansion cycle, a large negative pressure overcomes the liquid's tensile strength, resulting in gaps (Yu et al., 2020).  have demonstrated that ultrasonically engineered interfaces have porous morphology, high surface area and high stability. They also suggested that the porous matrix could be loaded with antimicrobial compounds and covered by various types of coatings and could be used as a multifunctional surface due to its antimicrobial function and selfcleaning .
One of the main aims of using ultrasonic cleaning is to reduce biofilm adherence. Brasil et al. (2017) evaluated the combination of ultrasound with chlorinated water and detergent (neutral) as a novel non-thermal treatment for the cleaning and sanitation of knives used in slaughter houses. They observed that ultrasound treatment leads to the reduction of cleaning and decontamination temperatures of knives, at the same time cleaning of knives was found to be more uniform, and the structure of knives was also not modified by ultrasound (Brasil et al., 2017). Yu et al. (2021) have evaluated the combined treatment of ClO 2 and highintensity ultrasound to assess the synergistic effect on S. aureus biofilm detachment and biofilm cell inactivation on food contact material. Confocal laser scanning microscopy (CLSM) and SEM evaluation revealed that the combination treatment had the best bactericidal impact as well as the dispersion and detachment of S. aureus biofilms. With the combined treatment, the surface roughness of food contact materials was noticeable, and it was adversely linked with the biofilm clearing rate .

Cold plasma technology
A novel and versatile approach for the manufacturing of antimicrobial materials could be served by non-thermal plasma-based technology. Unlike "wet" technology, which is sensitive to the properties of the substrate, the deposition of plasma could be used as an antimicrobial coating and grafting on a wide range of materials such as polymers, metals and ceramics, including temperature-sensitive and moisture sensitive equipment. The cold plasma technique is a "rapid, waterless, zero-contact, chemical-free" tool for the removal of pathogens from food contact surfaces (Niemira et al., 2014). This approach produces a wide range of reactive oxygen species (ROS) that are sufficient for the complete bacterial load in the semi-neutral plasma system, including bacterial spores and spoilage/pathogenic microorganisms. In terms of food decontamination, this is the system's greatest advantage (Choi et al., 2017;Olatunde et al., 2021;Umair et al., 2021). Romani et al. (2020) had developed bi-layer protein solution films followed by plasma treatment (glow discharge) and coating with carnauba wax. They observed that the combination of cold plasma and carnauba wax coating improved the packaging quality in terms of tensile strength and water vapour permeability (Romani et al., 2020). Dasan et al. (2017) used a micro-plasma system with gliding arc discharge (GAD) and observed the decontamination of stainless steel, polyethylene terephthalate and silicone surfaces (Dasan et al., 2017). GAD is recommended because of its minimal equipment and operating expenses, as well as its excellent efficiency in inactivating a variety of bacteria.
Currently, the focus is on the plasma polymer film, which is deposited by plasma-enhanced chemical vapour deposition. These films have remarkable properties, such as the ability to change properties by varying a parameter or precursor, excellent adhesion, and a highly crosslinked structure. Additionally, the reduction in the use of chemical solvents by the plasma engineering of materials makes them more suitable for industrial use. The proper regulation of the parameters of the plasma source and the depositional structure arranges the chances for the synthesis of advanced composite films or complex hybrids. Kim et al. (2015) observed the bactericidal effect of an atmospheric pressure plasma (APP) jet on the biofilm formation of collagen casing (CC), polypropylene (PP) and polyethylene terephthalate (PET) against L. monocytogenes, E. coli O157: H7, and S. typhimurium (Kim et al., 2015). These films are most suitable for the engineering of the new class of biomaterial. Plasma treated and/or synthesised polymers serve as highly reactive surfaces as they are rich in free radicals. Therefore, these materials are engineered in such a way that free radicals lead to controllable surface functionalisation without changing the bulk properties of the material.
Plasma pre-treatment has been widely used to modify or activate the surface of the material. Plasma pre-treatment improves the surface incorporation efficacy of antimicrobial substances. In addition, grafting of chitosan onto the surface of poly (ethylene terephthalate) (PET) materials and polyethylene (PE) films with atmospheric pressure dielectric barrier discharge (DBD) plasma pre-treatment was reported (Sophonvachiraporn et al., 2011;Theapsak et al., 2012). Jacofsky and Watson (2016) used multi-frequency harmonic cold plasma treatment for the sanitisation of food transport conveyor belts and food contact surfaces for a specific period (Jacofsky & Watson, 2016).
To induce antimicrobial activity on the surface of the material, plasma polymerisation is found to be an effective approach. In some studies, nanoparticles are also incorporated into the material by the direct incorporation or on-site reduction of an attached metal cation into the zone of plasma polymerisation (Nikiforov et al., 2016). Chen et al. (2019) modified zein films by a two-step method involving compositing with chitosan followed by cold plasma treatment. They observed that after the 60-sec plasma treatment, the enhancement in the properties like thermal stability, tensile strength, and water vapor barrier (Chen et al., 2019). Katsigiannis et al. (2021) had evaluated the indirect Cold atmospheric pressure (CAP) plasma against two common foodborne pathogens (L. monocytogenes and S. typhimurium) on stainless steel surfaces. They observed, within 3 min, the system reduced L. monocytogenes and S. typhimurium to > 3.55 log CFU/mL and 2.06 logCFU/mL, respectively, at a distance of 5 mm. The stainless-steel surface morphology was observed to be unaffected by the CAP exposure (Katsigiannis et al. 2021).

Conclusion and future perspectives
The microbial interaction leads to the deterioration of the efficiency of food contact material and has a harmful effect on health. The major challenge for the food industry is to prevent the initial microbial attachment and killing the microbes or/and removing the dead bacteria from the food contact materials. It has been observed that several new or emerging technologies could enhance the efficiency of food contact materials by reducing microbial contamination. Technologies like surface functionalisation, high-intensity ultrasound and cold plasma technologies have a high potential to decontaminate surfaces. Multifunctional surfaces are need of the food industry, which is attainable by incorporating two or more functional elements. The formation and moderation of innovative surfaces with micro or nano-sized features and the alteration in surface topography will make the food contact surface resistant to the microbial attachment. The surface coating should have more functions, but it should not be toxic to human health. Therefore, the use of natural compounds in the development of the surface would be an ideal solution to enhancing the sanitisation process and modification of physicochemical properties of the surface. Though the safety and inertness of the food contact material is a subject of future research. A multifunctional antimicrobial coating and nanoscale surface topology would have a potential application in all processing areas of the food industry to improve the safety and inertness of the food contact material while maintaining the quality of food. In addition, the combination of two techniques, such as steam followed by ultrasound, could be a cost-effective solution.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.