Microbiological quality of broiler carcasses during slaughter processing

Microbial contamination of poultry carcasses can be influenced by many factors during transport and slaughtering. The aim of this study was to evaluate the impact of four processing steps (plucking, evisceration, washing and chilling) on the total viable counts (TVC), counts of Escherichia coli, Salmonella spp. and Listeria spp. incidence on broiler carcasses. A total of 160 broiler carcasses originating from one farm were collected during one year period at a Czech slaughterhouse and examined. Both TVC and E. coli counts decreased during processing from 4.6 log cfu/cm2 and 3.5 log cfu/cm2 to 3.7 log cfu/cm2 and 1.8 log cfu/cm2, respectively, with a major impact of washing on TVC and washing and chilling on E. coli decrease (P < 0.001). Both Salmonella spp. (6 strains) and Listeria spp. (12 strains, none of L. monocytogenes) were found sporadically in all processing steps followed. However, a decreasing trend was observed in Salmonella counts and Listeria spp. incidence during the processing. Thus, this study brings new valuable information on the dynamics of microflora during modern poultry processing. Poultry carcass, plucking, evisceration, chilling, microbial contamination, Escherichia coli, Listeria, Salmonella Over the past 20 years, poultry meat production and consumption worldwide has increased very rapidly. This has led to intensive animal production with an increase in both the number of farms and in flock size. Broilers are normally raised on litter floors and this may lead to contamination of poultry both with spoilage microorganisms and also with human pathogens, such as Salmonella spp., Campylobacter spp., Clostridium perfringens, Listeria monocytogenes and Escherichia coli or Staphylococcus aureus. Young animals show symptoms of bacterial infection only occasionally but most of them are healthy carriers of pathogens and they are not excluded from farm or from slaughter during ante mortem inspection. Epidemiological data suggest that contaminated products of animal origin, especially poultry, contribute significantly to foodborne diseases. Reduction of raw poultry contamination levels would thus have a large impact on reducing the incidence of illness (Keener et al. 2004). Transport and slaughter of poultry involve a number of operations that may substantially affect the extent of poultry contamination. Due to stress during transport, excretion patterns of birds carrying e.g. Salmonella can change through disturbance of intestinal function or even damage to the birds’ intestinal tract to such extent that they may adversely affect their immune system (Cox and Pavic 2010). An important process operation that impacts the presence of microorganisms in poultry slaughter is scalding. At present, the trend is to scald poultry at lower temperatures (50-52 °C), which are more suitable for air-chilled poultry. Lower scalding temperatures may, however, allow some microorganisms including pathogens to survive. A way of avoiding this problem is to use multistage scalding, where poultry is scalded in several ACTA VET. BRNO 2012, 81: 037–042; doi:10.2754/avb201281010037 Address for correspondence: MVDr. Irena Svobodová, Ph.D. University of Veterinary and Pharmaceutical Sciences Brno Faculty of Veterinary Hygiene and Ecology Department of Meat Hygiene and Technology Palackeho 1-3, 612 42 Brno, Czech Republic Phone: +420 541 562 746 Fax: +420 541 321 230 E-mail: [email protected] http://www.vfu.cz/acta-vet/actavet.htm scald tanks lined one behind another, which substantially reduces contamination on poultry surfaces (Berrang et al. 2008). The next process operation is plucking, which is closely related to the scalding operation. The main hygienic problem is cross-contamination via equipment or via aerosols in the air. Evisceration is the first stage of the clean part of the slaughter process. Consisting of several stages, evisceration starts with head removal followed by opening of the body cavity, removal of intestines, and ends with the cleaning of the carcass (Cox and Pavic 2010). From the hygienic point of view, attention is paid to the removal of the intestines and the prevention of cross-contamination with faecal material. The next processing step is chilling which is essential to control microbial growth (James et al. 2006). Common methods include continuous mechanical immersion, chilling and airblast chilling, with or without the incorporation of water-sprays to maintain product yield and enhance cooling by evaporation (Mead 2004). It follows from the above overview of basic processing steps in broiler slaughter that there are many steps in the poultry meat processing that could significantly influence the extent of poultry contamination and thus also its marketability and incidence of pathogenic microorganisms. The most critical processing steps in this respect include scalding, plucking, evisceration and the type of poultry chilling (Keener et al. 2004). The aim of this study was to evaluate the impact of four selected processing steps (plucking, evisceration, washing and chilling) on the dynamics of the total viable count (TVC), and counts of E. coli, Salmonella spp. and Listeria spp. Materials and Methods Sampling Samples of whole carcasses were obtained from a broiler processing plant during a one year period. The samples were collected eight times at regular 6-week intervals. All broilers came from one intensive poultry farm; using the all-in-all-out production system, the farm had a production capacity of 280,000 broilers. The average rearing period was 36 days (33–39 days), the average weight was 2.1 kg and the mortality on the farm was 3.6%. Broilers of Ross 308 and Cobb 500 hybrid lines were fed with a commercial feed mix with coccidiostats (nicarbazin and monensin), but without growth-promoting antibiotics. The farm was located 60 km from the slaughterhouse, so the journey duration was short in all cases. The poultry slaughter process was typical for the industry. It consisted of slaughtering, scalding at 54 ± 2 °C for 180 s, plucking, washing, evisceration and evaporative chilling for 70 min. An inside/outside washer was used for cleaning carcasses before chilling. The temperature in the chilling tunnel was less than 0 °C and the surface temperature of carcasses after chilling was less than 4 °C. The processing line had the capacity of 8,500 carcasses per hour. The samples were collected from four different points along the processing line. The first sampling point was at the line after plucking (including head removal and hock cutting), the second was after evisceration (including removal of gastrointestinal tract and lungs), the third was after washing before chilling and the last point was after evaporative chilling. Five broiler carcasses from each sampling point were collected (n = 20); a total of 160 broiler carcasses were analysed. Each sample was represented by the whole carcass, which was removed from the processing line. The samples were placed into a sterile plastic bag and sent in an insulated box with refrigerant gel packs to the laboratory. Microbiological analyses For microbiological analyses, the carcass was sampled by the whole carcass rinse (WCR) technique as described by Lindblad et al. (2006). Buffered peptone water (Merck, Germany) was used for sample dilution. Total viable counts were determined according ISO 4833:2003 standard method using Plate Count Agar (Merck) after incubation for 72 h at 30 °C. Escherichia coli were determined according ISO 16649-2:2001 standard method using Chromocult (TBX) agar (Merck) after incubation for 24 h at 44 °C. The presence of Salmonella spp. was determined according to modified ISO 6579:2003 standard method. As the selective agar media, XLT4 agar and Brilliant Green Agar were used, incubated at 37 °C for 24 h. After confirmation, isolates were serotyped and phagotyped at the National Institute of Public Health, Brno, Czech Republic. The most probable number (MPN) method was used for the counting of Salmonella spp. All the tubes were prepared in triplicate. Positive tubes were scored and the MPN values were calculated using Thomas’ equation (Blodgett 2006). All the media used for the determination of Salmonella spp. were purchased from Oxoid, United Kingdom. 38