Bacterial foodborne pathogens such as Salmonella (Hood and Zottola, 1997), Campylobacter (Nguyen et al., 2012), Arcobacter (Gibrau et al., 2017) and Listeria (Sofyan et al., 2006) have the ability to attach to processing equipment materials, and subsequently equipment contact surfaces may lead to bacterial contamination of poultry meat during processing (Giaouris et al., 2013). Therefore, poultry processing equipment must be designed, constructed and maintained to meet minimal sanitary criteria. These minimal criteria include: 1. Impermeable to water; 2. Resistant to wear and corrosion; and 3. Facilitated cleaning and sanitizing (Hubbert and Hagstad, 1991). While use of materials that meet entail these criteria have been a longterm practice by the poultry processing.
industry, recent foodborne disease outbreaks and food recalls in which the contaminant originated from the processing environment continue to emphasize the importance or preventing equipment surfaces from becoming contamination sources.
In regards to preventing processing equipment from becoming chronic sources of bacterial contaminants, there is an increasing emphasis on the sanitary design and materials used particularly in regards to decreasing or preventing bacterial attachment. The phenomenon of bacterial attachment to surfaces is complex and not fully understood. It is known that many factors including physiological state of bacterial cells and the physiochemical properties of the surfaces affect initial attachment (Goulter-Thorsen et al., 2011; Hui and Dykes, 2012; Mai and Conner, 2007; Nguyen et al., 2012). To reiterate, it is recognized that foodborne pathogens, once attached to food processing surfaces, can persist for extended periods and serve as a source of contamination in final products (Berrang et al., 2010; Berrang and Frank, 2012; Martin et al., 2011; Sakaridis et al., 2011; Spurlock and Zottola, 1991). Therefore, a better understanding of the role of processing equipment materials on attachment, establishment, and persistence of foodborne bacterial pathogens can lead to better control methods and improved food safety.
Austenitic stainless steels are the predominant materials used in a wide variety of poultry processing equipment (Spragg, 1977) because they are generally nonreactive, easily cleaned and corrosion resistant (Holah and Thorpe, 1990; Masurovsky and Jordan, 1958). Surface finish can be of great importance to the hygiene of stainless steel food contact surfaces; therefore, roughness standards have been established for stainless steel intended for food contact. (BoulangePetermann,1996). In response to increased concern over post-process contamination for ready-to-eat products, recent research has focused on the effects of stainless steel roughness and other surface properties on the initial attachment of microorganisms.
Sofyan et al. (2006) determined the attachment of Listeria monocytogenes to stainless steel 304 finished to No. 2B (mill), No. 4 (satin) and No. 8 (mirror) standards, and reported that cells attached at a greater rate to the mirror finished stainless steel as compared to the other two finishes, and more bacteria attached to the satin stainless steel vs the mill finished steel. GoulterThorsen et al. (2011) obtained similar results using Escherichia coli O157, although bacteria were more easily removed from mirror finished steel and attachment results were inconsistent on No. 4 finished stainless steel. In general, it is difficult to draw a direct correlation between surface physical properties (i.e., roughness, contact angle, etc.) and ability of bacteria to initially attach. Medilanski et al. (2002), found that bacterial attachment to stainless steel surfaces may not be related to surface roughness alone, but rather to the differences in surface topography or other factors. Attachment of Salmonella and Campylobacter to stainless steel also appears to be complex and dependent on factors beyond surface roughness (Giaouris et al., 2012; Nguyen et al., 2012).
Any disruption of a stainless steel’s food-grade finish can lead to a loss of cleanability and promote bacterial harborage sites. While stainless steel processing surfaces are typically welded during original manufacture, the weld areas are polished to a food-grade finish prior to installation (National Sanitation Foundation, 2000). This polishing is critical because welding can delete chromium from the weld zone, which causes a loss of corrosion-resistance. Without proper post-welding treatment, corrosion can occur in the weld region and corroded metal can harbor bacteria. Mai et al. (2006) reported that welding of austenitic stainless steel followed by polishing did not affect bacterial attachment; however, corrosion of welded stainless steel promoted bacterial attachment. Thus, processors who weld stainless steel for repairs and modifications should utilize welding techniques or post-welding treatments that minimize subsequent corrosion.
Other Materials and Consideration for the Poultry Processing Plant
Within a poultry processing plant, there are numerous contact and non-contact surfaces to which bacteria can attach and persist. Again, these surfaces need to meet the minimum sanitary criteria stated above (Hubbert and Hagstad, 1991). Arnold and Silvers (2000) investigated attachment of mixed bacteria to variety of materials found in poultry processing, including stainless steel, conveyor belting, polyethylene and picker-finger rubber. These researchers reported that while variation in affinity was observed, bacteria attached to steel, belting and polyethylene. However, attachment of the test bacteria was inhibited by the picker-finger rubber. Veluz et al. (2012) determined the attachment of Salmonella and L. monocytogenes to materials commonly used for poultry processing conveyor belts, including polyurethane with monopolyester fabric, acetal, polypropylene-meshtop, polypropylene, stainless steel single loop, and stainless steel balance weave. For both tested bacterial cultures attachment to all tested materials was observed; however, stainless steel was more resistant to attachment as compared to the plastic materials.
While surfaces that contact poultry during processing are of primary concern for cleanability and sanitation, non-contact surfaces may also harbor foodborne pathogens. Therefore, materials employed for use in poultry processing plant structures are also of concern from a food safety standpoint. For example, cast iron has be used for floor draining for many years. Spurlock and Zottola (1991) demonstrated the ability of L. mononcytogenes to attach and form biofilms on cast iron surfaces, and concluded that floor drains could be a reservoir of this pathogen in food processing facilities. Additionally, walls, floors and ceilings can serve as sources of chronic bacterial contamination in food processing. Concrete, widely used in poultry processing environments, may be permeated with bacteria due to its microporous structure (Yang et al., 2004). Concrete floors, walls and ceilings in food processing environments typically are sealed with a waterproof treatment; however, sealants can be easily damaged or eroded over time or the concrete may crack. Exposed concrete and cracks provide bacterial harborages that can lead to chronic sources of environmental contamination of food products (Hubbert and Hagstad, 1991). Paiva et al. (2009, 2010) reported that a novel concrete sealant, a hydrosilicate catalyst in a colloid liquid base, reduced attachment of Salmonella spp. and Listeria spp. to concrete, and that the sealant prevented Salmonella spp. from penetrating into the structure of the concrete. In contrast Listeria spp. were recovered from the interior of inoculated concrete, which suggest that Listeria spp. exhibited the ability to penetrate into the microporous structure. When comparing results these researchers obtained with Salmonella spp. and Listeria spp., it appears that bacterial penetration of concrete microstructure is dependent on type of bacteria. Although the tested sealant did not prevent penetration of Listeria spp. into the concrete, it significantly reduced exterior and interior Listeria spp. when applied after bacterial inoculation. These researchers suggested that this tested concrete sealant had potential to reduce environmental Salmonella and Listeria when used in combination with other sanitation procedures.
Controlling product contamination during processing is a major food safety goal for all poultry processors. Use of hygienically designed, installed and maintained equipment is a sound strategy for helping achieve this goal. Materials used in the construction of processing plants also play a role in the establishment and persistence of environmental foodborne pathogens; therefore, the physical structure of the processing plant must be constructed in using proper materials and design. Recent research provides valuable information that poultry processors, equipment manufacturers and facility designers may use to enhance control of bacterial contaminants.
Presented at the XXV Latin American Poultry Congress in Guadalajara, Mexico.
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