If food contact surfaces are in constant use

FCS Management

FCS are those surfaces that contact human food and those surfaces from which drainage, or other transfer, onto the food or onto surfaces that contact the food ordinarily occurs during the normal course of operations. “FCS” includes utensils and FCS of equipment.

Controlling FCS within the zone is the key to effective sanitation controls. Pathogens must first gain entry to your facility through raw materials, personnel, or even the purchase of used equipment; anything brought into the production environment should be suspected. Once inside, they cannot fly or walk, they require a “ride” to move around the food facility; people, condensation, dust, and portable equipment can all provide such transport. Upon gaining entry to the zone, pathogens can take up residence within the area and eventually reach FCS by these same mechanisms.

FCS management becomes the focal point of preventing pathogen transfer between the environment and product. Understanding how this happens and managing the sanitary condition of contact surfaces is key to effective sanitation controls, that is, controlling the environment in the hygiene zone, and ultimately preventing product contamination, whether by pathogen or allergen.

Abstract

Food contact surfaces comprise all surfaces that may come into contact with food products during production, processing, and packaging. These surfaces are typically made of stainless steel or some kind of plastic material, but contact surfaces may also consist of other materials like wood, rubber, ceramics, or glass. Recent developments in food contact surface decontamination are described in this chapter, with an emphasis on emerging methods. Cleaning is not covered, nor is biofilm. The chapter is focused on emerging methods and agents and does not cover widely used agents like chlorine, iodine, quaternary ammonium compounds, carboxylic acid, and acid–anionic sanitizers.

The methods are grouped as nonthermal and thermal, and there is also an attempt to separate methods that rely on direct contact (liquid, foam), and those that do not (plasma, steam, and fogging). Furthermore, aspects of prevention of recontamination through hygienic design and physical barriers are described, as are future trends and sources of more information.

Decontamination of Food Contact Surfaces

Food contact surfaces, such as packaging material, cutting tools and conveyor belts, are an ongoing concern for contamination of food products, during transportation, processing and storage. Application of CAPP can be used to control the microbial load of such surfaces and assist in eliminating cross-contamination.

Niemira et al. (2014) studied the inactivation of Salmonella biofilms on a model food contact surface. The Salmonella biofilm was significantly inactivated by up to 2.1 log10 within 15 s of CAPP treatment. The antimicrobial effect of the CAPP treatment was consistent, regardless of the biofilms maturity. Recently, Toyokawa et al. (2017) developed a novel roller conveyer plasma device, which generates the plasma on the conveyer roller, for the decontamination of both surfaces, conveyer and product on it. Practical applicability was shown by the inactivation of Xanthomonas campestris pv. campestris inoculated on cabbage leafs. The application of CAPP can also be used for the real-time disinfection of rotating cutting devices, such as knifes for the meat industry (Leipold et al., 2010). This disinfection method (Fig. 3) can reduce the risk of cross-contamination between different meat batches during the slicing process. Besides the disinfection of conveyers and cutting devices, plasma can also be utilized for the microbial inactivation of food packaging materials, such as foils and bottles. Muranyi et al. (2007) showed the potential of a cascaded dielectric barrier discharge plasma in decontamination of PET foils. Within 1 s treatment time, Bacillus atrophaeus and pumilis, as well as Clostridium botulinum type A and Clostridium sporogenes spores could be inactivared by more than 5 log10. Ehlbeck et al. (2011) showed that humid plasma processed air is able to inactivate 5 log10 B. atrophaeus spores inoculated in glass bottles within 2 min treatment.

Equipment

Food contact surfaces are particularly important as a potential source of contamination, and sanitation (cleaning and disinfection) is the major day-to-day control measure. When undertaken correctly, sanitation programmes have been shown to be cost-effective and easy to manage and, if diligently applied, can significantly reduce the risk of microbial contamination (Holah and Thorpe, 2002). In this regard, microbial testing is useful in the validating standard sanitary operating procedures (SSOPs) and verifying that they have been carried out effectively.

Although a microbial surface may not be a source of contamination after sanitation, food residue on that surface during production can provide the opportunity for microbial growth, which could then be a source of recontamination for the product. With production pressures to keep lines running as long as possible between SSOPs, microbial testing can provide valuable information to maximise line efficiency without compromising the microbial safety or quality of the product.

Contamination of Food Contact Surfaces

On food contact surfaces organic, inorganic, chemical, and biological residues can accumulate during food processing. The occurrence of undesirable microorganisms in terms of spoilage microorganisms and food pathogens is of great concern. Especially food pathogens pose a risk of food poisoning even in low numbers while spoilage microorganisms affect the product quality only at higher numbers (Mafu et al., 2011). The EU regulation No. 852/2004 on the hygiene of foodstuffs (2004) defined that food contact surfaces have to be easy to clean and disinfect and have to be in a sound condition. Therefore, smooth, washable, corrosion-resistant, and non-toxic materials have to be used for food contact surfaces. Additionally, foodstuff transporting equipment has to be designed to allow adequate cleaning and disinfection and furthermore, they have to be kept clean and in good condition to avoid contaminations. While some microorganisms establish themselves in food production environments others can occur by coincidence. Nevertheless, most of the microorganisms found after cleaning and disinfection are non-pathogenic. However, monitoring of the microbial contamination is mostly limited to the total viable count without further identification of the microbial load. Therefore, the identity of the microorganisms is mostly unknown and knowledge about their impact on product safety and product quality is missing (Møretrø and Langsrud, 2017). In particular, biofilm formation in the food industry is a risk to the product safety and has to be monitored. Biofilm formation is depending on the occurring type and level of microorganisms, temperature, pH, nutrient, and time availability as well as surface condition and can be limited to some extend by regular cleaning and disinfection (Holah, 2014).

11.4.2 Surface finish

All food contact surfaces must be smooth, non-porous and easily cleanable (Holah and Thorpe, 1990) and free from large, randomly distributed irregularities such as pits, folds and crevices. The attachment and removal of food materials and microorganisms from surfaces is believed to be a function of the surface roughness such that the rougher the surface the longer the cleaning time. The Ra value is the most common measure of roughness, being defined as the ‘average departure of the surface profile from a calculated centre line’ (Verran, 2005) and is the most commonly used measure to define or specify a surface. While the Ra value gives an indication of the amplitude of the surface irregularities, it is based on a linear trace and hence gives no information on either the three-dimensional nature of the surface or the two-dimensional topography. Currently a maximum roughness of 0.8 μm has been specified for food contact surfaces both by the EHEDG and the American 3-A’s organisation (Curiel et al., 1993), although higher values are acceptable providing their cleanability can be demonstrated. The development of more sophisticated instruments such as atomic force microscopy (AFM) allows greater information on the surface topography to be obtained with the ability to provide Ra data on the nanometre scale together with an image of the area scanned (Verran, 2005).

5.3.4 Smooth surfaces

All food contact surfaces and joints should be smooth without pits, folds or crevices and surfaces projections, edges and recesses should be minimised. The common measure for surface roughness is the Ra value. This represents an average arithmetical departure of the surface profile from a centre line. The suggested value should not be greater than 0.8 μm for stainless steel. However, it should be noted that the value gives an indication of irregularities on a surface, but does not give information about its true topography. Thus higher values might be acceptable if it can be demonstrated that the surface is cleanable.

Permanent joints, such as welds, are preferred to dismountable joints. Welds must be smooth, continuous and free of overlaps. They should preferably be made automatically by means of orbital welding with sufficient gas shielding. If coupling is used, crevices must be avoided by using appropriate seamless gasket-to-metal design. In wet-cleaned equipment, there should be no metal-to-metal contacts which may present a hidden niche which would be virtually impossible to clean.

There should be no recessed fasteners on any surface of the equipment. The product contact areas should be free of exposed threads, screws, bolts, nuts or other fasteners which could become loose and present a problem. If fasteners are used, they must have compressible rubber washer and the nuts should be mounted on the outside of the equipment.

Inner surfaces in the food contact areas must have a radius which allows thorough cleaning. The radius of corners should be equal to or larger than 3 mm. Sharp corners with 90 ° angles or less should be avoided where possible.

21.2 Sampling surfaces

On food contact surfaces, the US Public Health Service recommends no more than 100 colony forming units (CFUs) per 50 cm2 sampled (28). However, in most cases the type of microorganism is more important than the number. Sampling and testing are the best means to monitor microbial activity on process surfaces; and for meaningful results, the appropriate sampling strategy for examining surfaces needs to be selected. Which sampling strategy used is dependent on the sampling surface material, surface structure, location, and expected microbial contamination level (109). Some sampling strategies include random, representative, selective, and convenience sampling (56). Food processing companies should develop a sampling program to selectively test identified hazards and risks at critical control points (CCPs) within their Hazard Analysis Critical Control Point (HACCP) system (28). Assessment should be performed at all sites with the potential to harbor microorganisms that may directly or indirectly contaminate the product. For instance, sampling should occur at points where there is higher risk of residual moisture and also at points that are representative of the production equipment. Thus, focus should not only be on direct food contact surfaces because microorganisms can be transferred from indirect contact surfaces to direct contact surfaces. Direct contact surfaces include the inside of pipes, conveyors, storage vessels, fillers, and mixers; and indirect contact surfaces include the outside of equipment, walls, floors, and tools. Sampling should always be performed sterilely to avoid contamination of the sample. Moreover, the sample should be properly labeled, stored, and transported and quickly analyzed after being collected (13).

Sampling methods can be qualitative or quantitative. Qualitative sampling detects the presence or absence of microorganisms at numbers above a given threshold; whereas, quantitative sampling determines the number of microorganisms on the sampled surface. Sampling methods inherently increase random error which decreases precision and systematic errors which cause deviations from true values (56). Errors in sampling are associated with the removal, recovery, and dispersal of living microorganisms within a sampled biofilm isolated from a processing surface. In quantitative sampling, approximately 95% of the replicate results should lie within plus or minus two standard deviations of the mean (59).

There are two main sampling methods that have been found acceptable: indirect and direct sampling (13, 28). In indirect surface sampling, the most common method is the rinse test. The rinse method can be used to sample containers and processing equipment systems such as tanks, pipelines, and fillers or areas inaccessible to direct sampling. The test involves rinsing a large area of the surface and collecting the rinse water. Water used for rinsing should be heat sterilized, filter sterilized, or chlorinated followed by neutralization (28). The rinse water is usually added upstream of the process and collected downstream at various points in the process for sampling. The number of CFUs is then obtained from the rinse samples. Indirect sampling has the advantage of sampling a larger surface area and areas inaccessible without disassembling equipment. The disadvantages of indirect sampling are that it may not possibly provide enough shear force to remove biofilms physically attached to the surface and that large rinsing volumes yield high material and disposal costs (13).

Microbial assessment of contact surfaces is generally tested by direct contact methods. In direct surface sampling, the most common method is the swab test. The swab contact method involves using a sterile nonabsorbent swab (e.g., cotton, calcium alginate, Dacron, or rayon) to sample the surface (13, 27, 28). The swab is first moistened with rinse solution and then rubbed slowly and thoroughly over the surface to be sampled with rinsing after each swab. Generally, swabs are used to wipe a defined area (e.g., 25 cm2) of the surface and can be used for surfaces with cracks, corners, or crevices. Flexible stencils made of inert materials like Teflon® or silicon can be used to mark the area to be sampled. Since sampling is mechanical, attached biofilms can be sampled. After sampling, the swab is broken or cut and collected in small vials containing buffered rinse solution with appropriate neutralizers. The sample can be used for both qualitative and quantitative analyses. For quantitative analysis, accurate enumeration depends greatly on the ability of the swab to remove microorganisms from the surface, the release of the microorganisms from the swab into an enrichment media. The type of swab and media used for sampling greatly affects the number of microorganisms detected (74). Underestimation may be due to microorganisms becoming injured during swabbing (73). Other disadvantages of swabbing include a small sample area and low reproducibility and repeatability due to variation among sampling technique such as amount of pressure applied when rubbing (86). For instance, applying too little pressure may cause microorganisms to remain adhered to the surface and applying too much pressure can damage the swab (98). Self-contained media-based swabs include a semi-solid selective agar culture tube for microbial detection (73). These swabs have been found to be more sensitive than traditional swabbing techniques but only give qualitative data. Sampled areas should be carefully cleaned after use with 70% alcohol to prevent agar residue from promoting growth (13).

An alternative to swabs are sponges, which can sample large surface areas and identify areas that harbor pathogens for better control. The sponge contact method involves using sterile cellulose or polyurethane sponges free of antimicrobial preservatives (28). When sampling, sterile tongs or gloves should be used to hold the sponge. The sponge is moistened with rinse solution and rubbed over the surface (up to several meters). After sampling, the sponge is placed in a sterile plastic bag. The sponge can be introduced directly into enrichment broth or diluent can be added to the bag. Before analysis the sponge should be massaged in the diluent to release the microorganisms.

Another commonly used method involves using solid culture media in the form of a RODAC plate (Replicate Organism Detection and Counting), which consists of a plastic dish containing convex culture medium (6). The RODAC plate (agar contact) method is a simple method for sampling flat surfaces that have been previously cleaned or sanitized. It should not be used for crevices, curved and irregular surfaces, difficult to access areas, or heavily contaminated areas. During sampling, a representative and random number of sites should be obtained (101). The RODAC plate should be free of condensation and pressed against the surface so that the entire agar meniscus contacts the surface for 5–10 seconds (28). Applied pressure and contact time need to be optimized. This method is more sensitive than swabbing when the surface density of attached cells on surfaces is low with a recovery rate of 80% versus 1%, respectively (86). When surface density is high, the RODAC plate method will underestimate the number.

Commercially available alternatives to RODAC plates are PetriFilm™ (2M medical-Surgical Division, St. Paul, Minn.), Con-Tact-It (Birko Chemical Corp., Dever, Colo.), and dip slides (BIOSAN Laboratories, Inc., Warren, Mich.) (28, 73). The Petrifilm™ aerobic count or direct-contact method is a simple way to sample flat or curved surfaces but should not be used for surfaces with crevices or cracks. Plates come sealed in foiled pouches and need to be prehydrated before use with sterile water. When sampling, the top film with the gel should be lifted and pressed against the sample surface. Then the top film is placed back onto the bottom film and incubated. The Con-Tact-it® method is also a simple method to sample surfaces. When sampling, a fresh piece of tape is removed from the dispenser and pressed onto the surface to be tested. Then it is pressed onto the Con-Tact-it Petri plate of selective media, leaving one zone as a control, and incubated. Dipslides, which consist of nutrient agar on a sampling paddle, are another method to sample surfaces. When sampling, the contact slide is removed from its tube and pressed against the surface to be tested. Then the slide is turned over and pressed again against the surface. The slide is returned to the tube and incubated for 24–48 hours. Contamination levels are assessed by using a comparison chart provided in the commercially available kits.

Given all sampling techniques have limitations that bias results, it is recommended to compare results from more than one method to obtain representative data (98). Good hygienic design of equipment should minimize problematic sites (e.g., joints, pipe corners, gaskets, and o-rings, and fasteners) where contamination may occur. Furthermore, materials used in food processing should withstand a wide range of temperatures and be durable so that the surface is free of cracks, scratches, and pits, and most importantly microorganisms (66).

Type of Microorganisms on Food Surfaces

Microbial contamination of food-processing surfaces, equipment, and facilities with pathogenic microorganisms can lead to disease transmission. Several pathogenic microorganisms (some of them potentially deadly) have been associated with food-surface contamination. This includes several Gram-negative bacteria (e.g., Escherichia coli, including the O157:H7 serotype, Shigella spp., Salmonella spp., Serratia spp., Pseudomonas spp.), Gram-positive bacteria (e.g., Staphylococcus aureus, Listeria monocytogenes, Clostridium perfringens, Bacillus cereus), protozoan parasites (e.g., Cryptosporidium spp.), enteric viruses (e.g., noroviruses, hepatitis A virus), and foodborne fungi (e.g., Penicillium spp., Fusarium spp.). Bacterial spore-formers, such as members of the genera Clostridium and Bacillus, are especially difficult to kill with commonly used sanitizers and disinfectants. Several microorganisms, including many pathogens, can attach to food-contact surfaces and survive for extended periods of time, thus further demonstrating the need for proper sanitization.

Formation of surface conditioning films

The conditioning of food contact surfaces involves the accumulation of organic and inorganic components or molecules (proteins, lipids, nucleic acids, and other biomolecules) released from foods such as milk, meat, and fruits, resulting in an increased concentration of nutrients on formerly ‘clean’ surfaces. Sorption of these molecules alters the surface's physicochemical properties (surface free energy, hydrophobicity, and electrostatic charge) (Bryers, 1987; Sjollema et al., 1988; 1990) and plays a key role during the initial attachment of individual bacterial cells that precedes the more serious colonial biofilm formation (Kumar and Anand, 1998). Microorganisms may be transported to these conditioned surfaces along with the nutrients via simple diffusion gradients, advective mechanisms, or by directed (chemotactic) motility where the organic film on the surface acts as a ‘attractant’ for bacterial chemoreceptors (Lawrence et al., 1996). If left unchecked, a biofilm composed of living and dead cells, bacterial polymers and non-bacterial organic exudates, and inorganic compounds ultimately accumulates (Korber and Lawrence, 2004; Sampathkumar et al., 2004), often causing prolonged sanitation issues via cross-contamination. Thus, it is often important that food contact surfaces be cleaned and sanitized following each shift to remove conditioning films along with the pioneer colonizing cells to avoid formation of a persistent biofilm (see section on practical considerations below).