Distribution of airborne microorganisms in commercial pork slaughter processes
Introduction
Pork carcasses may be contaminated with pathogens during slaughter and processing. The prevention and/or reduction of such contamination is a major objective of Hazard Analysis and Critical Control Point (HACCP) systems, and related pre-requisite programmes such as the adoption of Good Manufacturing Practices (GMP). Such programmes usually encompass general cleaning and maintenance of abattoir, plant and equipment, but less frequently include steps to prevent the air in the abattoir acting as a vector of contaminants of carcasses and equipment.
Air has been established as a source of bacterial contamination in a range of slaughter and processing facilities (Knudtson and Hartman, 1993). The majority of studies have focused on the dairy industry (Radmore and Luck, 1984, Kang and Frank, 1989, Ren and Frank, 1992), with some studies examining airborne bacterial contamination in cattle (Jericho et al., 2000), and poultry (Ellerbroek, 1997, Whyte et al., 2001) slaughtering plants. However information on airborne contamination of pork slaughter plants is limited (Kotula and Emswiler-Rose, 1988), with little consideration of the potentially high risk slaughter and dressing areas of such operations.
Numerous studies have shown that animals moving from the farm to the slaughter environment are a major source of bacterial contamination (Epling et al., 1993, Davies et al., 1999, Letellier et al., 1999, Bolton et al., 2002). For example, a previous study by our group detected Salmonella on up to 31% of pig carcasses entering the abattoir investigated in this study (Pearce et al., 2004). It is likely that a portion of these and other pathogens may be present in the air within abattoirs, as dust or aerosols, where they may survive for extended periods. For example, McDermid and Lever (1996) have shown that Salmonella can survive in aerosols at 24 °C and 75% relative humidity for periods exceeding 24 h. Pathogens surviving in aerosols or dust may be carried throughout the plant and adhere to a range of uncontaminated surfaces, including carcasses and meat contact surfaces. Bacteria in aerosols or dust may affect product shelf life, and have food safety implications. For example, Rahkio and Korkeala (1997) demonstrated a strong association between air and carcass contamination levels in pigs and cattle.
Increasing recognition of the potential role of air as a vector for bacterial contamination, has led to suggestions that alternative plant layout/designs could restrict air movement. Such restrictions could significantly improve air quality, particularly in the later, “clean” stages of processing and so enhance product quality and shelf life. Suggestions in this regard include the construction of walls, and other separating structures, between “dirty” and “clean” processes (Worfel et al., 1996), or greater spatial separation of activities (Rahkio and Korkeala, 1997). However, the efficient implementation of such potentially expensive changes in slaughter and dressing operations must be based on guidelines derived from accurate and comprehensive data on the incidences and concentrations of airborne bacteria within these processes (Sofos, 1993, Kukay et al., 1996). Therefore this study was performed to assess the presence of bacteria, in particular Escherichia coli and Salmonella, in the air at various stages of pork slaughter in a commercial pork plant in Ireland.
Section snippets
Plant and process
The study investigated the aerobiology of a commercial pork processing facility where approximately 1000 pigs per day are slaughtered (Fig. 1). In this plant, animals were held in lairage, stunned using carbon dioxide, transferred into the “wet” room, and immediately exsanguinated by severing the carotid arteries and jugular veins. The animals were then pulled through a scalding tank, at 61 °C (± 1 °C), for approx. 8 min, dehaired, ejected onto a gambrelling table, hoisted onto an overhead
Results
Aerobic mesophilic bacteria from impaction samples taken at each location, before and during processing, are presented in Table 1. Before commencement of operations, there were no significant differences among the mean counts from the seven locations. After 2 h of operation, mean aerobic mesophilic bacteria from the wet room were significantly higher (P < 0.05) than those from the clean room or the chiller. From 8 h of operations onwards there were no significant differences between mean aerobic
Discussion
This study established strong correlations between counts obtained by air sampling and by sedimentation sampling, at most sampling locations within the examined plant. This observation suggests that there may be a close relationship between the types and numbers of bacteria suspended or aerosolised in air, and the types and numbers of bacteria which impinge onto surfaces, including those of carcasses and equipment in the slaughter facility. This is in agreement with the findings of Rahkio and
Acknowledgements
The authors wish to acknowledge Ms. Paula Reid, who performed the statistical analysis. This work has been funded by the United States/Ireland Co-operation Programme in Agriculture Science and Technology.
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