Poultry is a important part of the animal food market and production is increasing to satisfy public demand world-wide (Bryan 1980; Anand et al., 1989). Poultry and its products are also a major dietary item for the South African population (Bok et al., 1986). According to the Directorate of Veterinary Public Health, 4.4 billion rands worth of poultry meat products were purchased by South Africans in 1994 (AFMA, 1996; SAPA, 1996). Therefore, it becomes necessary to maintain absolute hygiene and strict control at different stages of processing to produce a safe and wholesome chicken product. Healthy chickens ready for processing harbour a tremendous amount and variety of bacteria. These bacteria are present on the surfaces of feet, feathers, skin and also in the intestines. During processing, a high proportion of these organisms will be removed, but further contamination can occur at any stage of the processing operation. The procedure for converting a live, healthy bird into a safe and wholesome poultry product provides many opportunities for micro-organisms to colonise on the surface of the carcase. During the various processing operations, opportunities exist for the contamination of the carcases from the environment, the process in the plant itself, contamination via knives, equipment, the hands of workers and also by cross-contamination from carcase to carcase. Some processing operations encourage an increase of contamination or even multiplication of contaminating organisms. As a result, the microbial population changes from mainly Gram-positive rods and micrococci on the outside of the live chicken to Gram-negative micro-organisms on the finished product (Bryan, 1980; Thomas et al., 1980; Eustace, 1981; Roberts, 1982; Grau, 1986; Bailey et al., 1987; Connor et al., 1987; Banwart, 1989; Mead, 1989). Poultry processing has a number of unique features which make control of microbial contamination more difficult than the processing of any other conventional meat animal. Among them is the rapid rate of processing in some processing plants, a condition which favours the spread of micro-organisms. The carcase must be kept whole throughout the process and the viscera have to be removed rapidly through a small opening in the abdomen without breakage, to minimise contamination of the carcase with intestinal organisms. After defeathering, the skin provides a complex surface with many holes which are capable of trapping bacteria (Mead, 1982; Grau, 1986; Mead, 1989). The micro-organisms are widely distributed over the carcases under normal circumstances and are spread over the skin during scalding and defeathering and on the inner and outer surfaces during evisceration and further processing (Bailey et al., 1987). Efforts should be made to prevent the build-up of contamination peaks during processing. Rinsing of the carcases, especially during defeathering and evisceration is therefore of great importance (McMeekin et al., 1979a; Brown et al., 1982; Mead, 1982; Anand et al., 1989; Mead, 1989). Spoilage bacteria grow mainly on the skin surfaces, in the feather follicles and on cut muscle surfaces under the skin. The nature and rate of attachment of the micro-organisms depends upon several factors including the bacteria involved and their concentration and also the conditions under which attachment occurs, namely, pH, temperature and contact-time. It was also found that Pseudomonas strains attach to meat surfaces more rapidly than any other bacteria (Firstenberg-Eden, 1981). The structure of the skin also has a crucial influence on attachment of bacteria. The organisms adhere by way of flagella and fimbrae and cannot easily be removed by rinsing, especially after a delay. There is still some disagreement on the role and importance of flagella in the attachment process of bacteria to meat. Research also shows that mesophilic bacteria are more heat-resistant when attached to skin than are the same bacteria not attached. (Barnes et al., 1973; Green, 1974; Notermans et al., 1974; Notermans et al., 1975; Harrigan, 1976; Firstenberg-Eden, 1981; Thomas et al., 1981; Faber et al., 1984; Lillard, 1985). The skin serves as a barrier to micro-organisms that might otherwise contaminate the underlying muscle and therefore the deep muscles are normally free of bacteria (Bryan, 1980; Mead, 1982). The few bacteria found in the deep muscle are of types that can only multiply slowly or not at all at low temperatures. The important microbiological changes take place on the surfaces of the carcases. It appears that some parts of the carcase are more favourable than others for bacterial growth, depending on the type of muscle and pH. Studies conducted over the last few years show that the sites most heavily contaminated are the neck skin and less frequently on the back and the area around the vent. Fewer organisms are found around the breast, legs and under the wings. Acinetobacter and Alteromonas grow better in leg muscle where pH is 6.4 to 6.7 than in breast muscle where pH is 5.7 to 5.9. Pseudomonas spp. can grow well at both pH ranges (Patterson, 1972; Barnes et al., 1973; Green, 1974; McMeekin et al., 1979a; Bryan, 1980; Thomas et al., 1981; Mead, 1982; Gill, 1983; Grau, 1986; Anand et al., 1989). The presumable reason for the neck skin being the most heavily contaminated is that the washings from the rest of the carcase run down the neck while the carcase hangs on the conveyor (Patterson, 1972; Connor et al., 1987).
Microbiology of poultry Contaminants may be micro-organisms that cause spoilage of the product or organisms of public health significance. Pathogens associated with poultry are Salmonella, Staphylococcus aureus, Clostridium perfringens and Escherichia coli. Listeria monocytogenes and Campylobacter jejuni have also been isolated from poultry. Spoilage bacteria most frequently associated with poultry are Pseudomonas spp., Acinetobacter, Moraxella, Alteromonas putrefaciens, Aeromonas spp., Corynebacterium, Flavobacterium, Micrococcaceae and Enterobacteriaceae. Poultry is a common vehicle of foodborne illness (See Table 1.1) (Bryan, 1980; Todd, 1980; Smeltzer, 1981; Brown et al., 1982; Mead, 1982;Roberts, 1982; Ralph et al., 1984; Evans, 1986; Gill, 1986; Grau,1986; Silliker et al., 1986; Cunningham 1987; Banwart, 1989; Mead, 1989; Zottola et al., 1990; Jones et al., 1991).
Salmonella are the main cause of food poisoning from poultry meat (Dougherty, 1976; Todd, 1980). Little is known about the incidence of Salmonella in South Africa although figures have been reported by Bok et al., 1986 and Geornaras et al., 1994. There are many sources from which poultry may obtain Salmonella, the main sources being from cross-contamination during breeding, hatching and intensive rearing operations. Salmonellas are not part of the normal intestinal microflora of poultry, but are acquired from the farm environment via insects, rodents and birds. Feed is also an important source of salmonellas through contamination of various components of the feed mix. The organisms occur more often in the caecum than in any other region of the gut from where they may be excreted for varying periods, without the host showing any sign of disease (Morris et al., 1970; Mead, 1982; Grau, 1986; Silliker et al., 1986; Mead, 1989; Zottola et al., 1990; Jones et al., 1991). Salmonellas from one flock can contaminate another, usually during conditions of intensive rearing and also when there is inadequate cleaning and disinfecting of the multi-cage transportation lorries used to convey the birds to the abattoir. Studies have also shown that live poultry transported from the farm often introduce Salmonella into the processing plant. Such contamination may result in considerable scattering of salmonellae during processing especially in the plucking machines and the scalding tank and may lead to contamination of the final product (McBride et al., 1980; Mead, 1982; Mead, 1989; James et al., 1992). Clostridium perfringens Clostridium perfringens is considered to be more widespread in the environment than any other pathogenic bacteria. This organism is commonly present in the intestinal tract of many warm-blooded animals and has been isolated from fecal matter, soil and dust. Raw poultry meat is normally stored at temperatures too low (< 15°C) to permit Clostridium perfringens to grow. Therefore, there seems little risk of multiplication in the processing plant. Clostridium perfringens is mainly present on processed poultry as spores ( Bryan, 1980; Todd, 1980; Mead, 1982; Bailey et al., 1987; Mead, 1989). Only type A strains are normally involved in human food poisoning and these may be haemolytic, with heat-sensitive spores or non-haemolytic, with spores that are highly heat resistant. These heat-resistant strains can survive normal cooking procedures and if the cooked meat is held under favourable conditions, the organism can multiply to hazardous levels (Todd, 1980; Mead, 1989; Zottola et al., 1990).
Food poisoning from poultry meat caused by Staphylococcus aureus is much less common than that due to salmonellas or Clostridium perfringens (Todd, 1980; Mead, 1982). Staphylococcus is important in relation to poultry meat, because it can produce enterotoxins which may cause food poisoning in humans (Notermans et al., 1982). Live poultry carry Staphylococcus aureus on skin surfaces and in nasal cavities, but low numbers are also present in the intestinal tract (Todd, 1980; Evans, 1986; Grau, 1986; Mead, 1989). Isolates of Staphylococcus aureus from poultry can be subdivided into human, non-human and intermediate types (Gibbs et al., 1978; Mead 1989). It appears that Staphylococcus aureus may also be obtained from human sources after hatching and during processing of the carcases (Gibbs et al., 1978; Mead, 1982). Notermans et al., 1982 indicated that after processing, contamination of carcases with this organism increased to >103 g-1 of skin. Defeathering machinery in particular may support the buildup of Staphylococcus aureus. Evisceration and chilling are also processing stages which have been incriminated in contaminating carcases with Staphylococcus aureus (Gibbs et al., 1978; Todd, 1980; Mead, 1982; Notermans et al., 1982; Mead, 1989).
Campylobacter is widely spread in nature and is isolated from wild and domestic animals as well as from the environment. Poultry is a major reservoir of Campylobacter jejuni. Many commercial poultry flocks appear to be symptomless carriers of C. jejuni, with up to 107.g-1 of gut content being demonstrated in the ileum and caeca of infected poultry and similar levels in the faeces (Genigeorgis et al., 1986; Mead, 1989; Zottola et al., 1990). Some poultry flocks that are negative before slaughter will therefore become contaminated during processing. Campylobacter is microaerophilic with a relative high minimum growth temperature (30°C) and there seems little likelihood of them multiplying in the processing plant or on the raw, processed product. The main problem in processing is that of cross-contamination (Zottola et al., 1990; Smeltzer, 1981). Campylobacter spp. are more sensitive than many other organisms to the adverse effects of environmental conditions (drying, freezing and cold storage). For this reason, attention has been given to factors influencing the survival of campylobacters in processing. Although freezing is harmfull to Campylobacter, it does not eliminate this organism from poultry. Nevertheless, the contamination rate tends to be higher in fresh than in frozen carcases. Campylobacter spp. are also more sensitive to chlorine than E. coli, but are not eliminated from poultry carcases by immersion chilling in chlorinated water. On the contrary, cooling-water seems to be an important reservoir of this organism: 100-3000 CFU.ml-1 were demonstrated and survival over long periods at low temperatures is possible. Campylobacter was also isolated from air samples as well as equipment (Cunningham, 1987; Mead, 1989; Zottola et al., 1990).
Listeria monocytogenes is widely distributed in nature and the environment. These organisms are isolated from soil, vegetation and faeces of humans and animals, with poultry often being contaminated. Studies also indicated that 57% (20 of 35 samples) and 33% (17 of 51 samples) of market poultry, respectively, contained L. monocytogenes. L. monocytogenes can multiply at refrigeration temperatures. Data also suggests that L. monocytogenes is more heat resistant in meat than Salmonella. The necessity of proper hygiene procedures in handling, processing and packaging of poultry is therefore emphasised (Zottola et al., 1990). 2.3 Spoilage organisms The spoilage of raw poultry meat is invariably due to the growth and metabolic activities of specific types of bacteria, the psychrotrophs (Ralph et al., 1984 Kraft, 1986; Mead 1989). Psychrotrophs most frequently associated with poultry are Acinetobacter, Moraxella, Alteromonas putrefaciens, Aeromonas spp., Flavobacterium spp., Corynebacterium, Micrococcaceae, Enterobacteriaceae, Serratia liquefaciens, the pigmented and non-pigmented Pseudomonas spp. and also yeast and moulds (Bryan, 1980; Kraft, 1986; Mead, 1989). The bacteria which usually predominate on spoiled carcases held below 10Â°C are the Pseudomonas (P.) spp., especially P. fluorescens, P. putida and P. fragi and also Acinetobacter and Moraxella (Bryan, 1980; Lahellec et al., 1981; Ralph, 1984; Mead, 1989). Some spoilage bacteria originate from the rearing environment and these organisms are carried in large numbers on the feet and feathers of poultry. These bacteria are not found in the intestines of poultry (Mead, 1982; Grau, 1986; Bailey et al., 1987). Prior to slaughter, the incoming chickens are contaminated with a large number of spoilage bacteria, but most are destroyed when passing through the scald tank, such as Acinetobacter, Moraxella, Pseudomonas, Corynebacterium and Flavobacterium (Lahellec et al., 1979; Mead, 1989). Pseudomonas, however, form a small proportion of psychrotrophic flora on the outside of the chicken (Mead, 1982). Recontamination occurs during various processing stages, because the organisms multiply on all wet surfaces, including the carcases (Bryan, 1980; Mead, 1989). Another possible source of spoilage bacteria is also the processing plant water-supply. The Pseudomonas are more resistant to chlorine than Escherichia coli and therefore may survive normal water treatment in the processing plant. Pseudomonas can be eliminated by super-chlorination of water at the processing plant The quality of water in the processing plant is therefore of great importance. Essential steps to prevent excessive levels of contamination include prompt washing and chilling of eviscerated poultry and effective cleaning and disinfection procedures for equipment and working surfaces at the end of the processing day, prior to the next days production (Lahellec et al., 1979; Mead, 1989). The growth of spoilage bacteria and thus the shelf-life of raw poultry meat, stored under chill conditions, will depend on the numbers and types of spoilage organisms present immediately after processing, the storage time and temperature, the type of tissue (skin or muscle), the pH, the redox potential, the type of packaging and the presence or absence of carbon dioxide (Bryan, 1980; Ralph et al., 1984; Mead, 1989).
Time and Temperature
Psychrotrophs can grow at temperatures of -3°C, but most do not multiply above 34°C (Mead, 1989). Psychrotrophic Pseudomonas become the predominant flora on the aerobic surfaces of poultry stored at low temperatures and they can multiply the entire time carcases are held at commonly used refrigerator temperatures (Bryan, 1980). There is a simple relationship between storage temperature and shelf-life under aerobic conditions and for any given chill temperature this is related to the doubling time of the spoilage organisms (Barnes, 1976). The differential effect of storage temperature on the microbial growth rates influences the composition of the ultimate spoilage organisms. Pseudomonas predominated at spoilage when poultry carcases were held at 1°C. Above 10°C, however the predominant organisms comprised mainly Acinetobacter spp. and Enterobacter (McMeekin, 1975; Mead, 1982). Fewer organisms are capable of growth at 4°C and those which do so often undergo a lengthy lag phase (Mead, 1982).
Meat pH and type of muscle
Although most carcase contaminants are found on the skin and over the inner surface of the visceral cavity, the growth of spoilage bacteria during chill storage conditions occurs primarily on cut muscle tissue and in the feather holes (Mead, 1982; Grau, 1986; Mead, 1989). Some parts of the chicken carcase appear to be more favourable than others for bacterial growth, depending on the muscle type and pH (Barnes, 1976). Pigmented and non-pigmented strains of Pseudomonas spp. grew equally well in the breast (pH 5,7 – 5,9) and in leg muscle (pH 6,4 – 6,7)(Mead, 1982). Acinetobacter – Moraxella spp. grew better in leg muscle, but not in breast muscle, whilst Shewanella grew faster in leg than in breast (Mead, 1982; Grau, 1986). Therefore one might expect to find different bacteria growing on the various cut muscle surfaces of spoiling carcases. The possibility also exists that spoilage may be more rapid in the high pH areas (Barnes, 1976).
Packaging and carbon dioxide
Apart from the tendency to retain moisture, the most important property of packaging film in relation to shelf-life is the permeability to oxygen and carbon dioxide (Mead, 1982). It was also shown that chicken carcases stored at 1°C in impermeable vacuum packs (vinylidene chloride-vinyl chloride copolymer) kept for ca. 5 days longer than those packed in gas-permeable polyethylene (Barnes, 1976; Mead, 1982). Pseudomonas spp. are the principal causes of spoilage on carcases packed in oxygen-permeable films, while Shewanella putrefaciens were the principal cause of spoilage of poultry carcases packed in oxygen impermeable films (Barnes, 1976; Bryan, 1980; Gill, 1983).
Influence of processing on poultry
The main operations in processing poultry are as follows: birds are removed from crates, hung by the feet on shackles on a conveyor, stunned by a low voltage electric shock in a water bath and killed by exsanguination following slitting of the neck and severing the carotid arteries. They are then scalded, defeathered and washed. Heads, feet and the viscera are removed. The carcases are then washed and chilled in cold water or in humidified air. After chilling, the carcases are further processed or packaged and stored chilled or frozen (Fig. 1.1) (McMeekin et al., 1979; Bailey et al., 1987; Bryan, 1980, Mead, 1982; Grau, 1986). During each stage of the process, opportunity exists for the contamination of the carcases with micro-organisms from the environment of the poultry processing plant or by cross-contamination from other birds (McMeekin et al., 1979). Numbers of bacteria on carcase surfaces vary considerably at different stages of processing and increases and decreases in numbers have been demonstrated (Thomas et al., 1980). Defeathering and evisceration are the two stages where bacterial contamination mostly takes place (Mead, 1982; Grau, 1986).
Pre-slaughter handling and transportation
For transportation to the processing plant, birds are usually caged in batches. However, stress caused by transport, crowding and exposure to weather conditions may lead to an increased frequency of defecation and discharge of ceacal contents (Grau, 1986; Mead,1982; Parry, 1989). In the little space available, birds tend to stand in an accumulation of their own droppings. Cages with solid floors used during transportation enable birds to sit in accumulated droppings. On the other hand, cages with perforated floors allow birds at higher levels to contaminate birds at lower levels (Mead, 1982; Grau, 1986; Mead, 1989). There is evidence that stress occurring during transportation can increase theproportion of birds which are intestinal carriers of Salmonella (Mead, 1982). It is therefore usual to starve birds before slaughter in order to minimise faecal contamination of carcases during transportation and processing (Anand et al., 1989; Mead, 1989). During unloading, it is inevitable that some birds will struggle and flap their wings as they are hung on the shackles, and this results in a considerable scattering of dust and
Carcases are scalded to loosen the feathers by immersion in a hot water tank, at either 50 – 52°C (soft scalding) or at 56°C to 60°C (hard scalding) (Bailey et al., 1987; Mead, 1989). During scalding micro-organisms on the skin and feathers and in the faeces of the birds are washed from the birds and continually released into the water of the scald tank. Aerobic plate counts of scald water however, are usually less than 5×104 cfu ml-1 of scald water (Mulder et al., 1974; Bryan, 1980). The survival of Enterobacteriaceae and mesophiles is higher at low scald temperatures of 50°C to 54°C than at higher temperatures (Grau, 1986; Anand et al., 1989). At a scald temperature of 61°C, reductions of more than 1000-fold can be obtained, whereas at scald temperatures of53°C to 55,5°C the counts are reduced by 10 to 100-fold (McBride et al., 1980; Notermans et al., 1980; Grau, 1986). The accumulation and survival of micro-organisms in the scald tank during processing is influenced by the temperature of scalding and the rate at which fresh water is added (Mead, 1982; Bryan, 1986; Bailey et al., 1987). The great reduction in counts during scalding and the absence of Pseudomonas indicate that scald water contamination plays a relative minor role in spoilage of chicken carcases(Bailey et al., 1987). Scald temperatures have little effect on the spores of Clostridium perfringens in the water (Mead, 1982; Bailey et al., 1987). Evidence also indicates that the shelf-life of carcases is reduced by scalding at temperatures above 58°C. This can be attributed to the fact that scalding at about 58°C – 60°C (hard scalding) and above, followed by mechanical plucking results in removal of the outer epidermal layer (cuticle),whereas scalding at 52°C – 53°C (soft scalding) does not. The cuticle free skin of the carcases serves as a more suitable substrate for spoilage organisms and in particular Pseudomonas (Bryan, 1980; Bailey et al., 1987).
During defeathering there is a considerable scattering of micro-organisms from carcase to carcase and also from the defeathering equipment itself. The warm, moist conditions under which these operations take place also favour microbial growth. There are two aspects to the contaminating effect of defeathering. One arises from the extensive aerial scattering of micro-organisms in the vicinity of the machines, and is due to their mechanical action (Mead, 1989). It is therefore necessary to ensure complete separation of the plucking and scalding area from the clean areas of processing (Zottola et al., 1990; Mead, 1989). The other aspect of defeathering hygiene is the nature of the machines themselves, and their siting next to the scald tank, which helps to maintain a warm moistenvironment suitable for microbial growth. The rubber “fingers” used to remove the feathers harbour micro-organisms and are not easily cleaned and disinfected (Mead,1982; Grau, 1986). Micro-organisms can persist in cracks and other imperfections even after vigorous cleaning (Gibbs et al., 1978; Grau, 1986). Up to 106 Staphylococcusaureus cm-2 can be found on the rubber “fingers” of defeathering machines and treatment with 100ppm chlorine for 30min may reduce the counts by only ca. tenfold (Gibbs et al., 1978). The counts of both aerobic mesophiles and psychrotrophs on poultry skin can increase during defeathering and also the numbers of Enterobacteriaceae (Lahellec et al., 1979; Thomas et al., 1980). Salmonella are also more frequently isolated from carcases after defeathering, than following any other processing operation (McBride et al., 1980). Following a hot or hard scalding, defeathering damages and removes the epidermal layer and exposes a new surface layer. This cuticle-free skin serves as a very suitable substrate for spoilage organisms and the organisms become trapped in the skin follicles and folds (Thomas et al., 1980; Grau, 1986; Connor et al., 1987; Mead, 1989).
During evisceration the opportunity exists for contamination with Enterobacteriaceae from the intestinal contents. Careless manual opening of the body cavities and manual evisceration leads to contamination of carcases, especially when the intestines are cut or the vent is inadequately loosened. Cross-contamination can also occur due to workers’ hands, evisceration implements and other slaughter equipment (Mead, 1982; Grau, 1986; Mead, 1989). No difference was found between plants using manual evisceration and those with automatic equipment, although automatic evisceration can cause considerable damage to carcases due to rupturing of the intestines when carcases in a particular batch varies in size (Mead, 1989). Aerobic mesophiles on the carcases usually do not increase significantly during evisceration, but the numbers of Enterobacteriaceae and the frequency of contamination with Salmonella often increase (Notermans et al., 1980; Grau, 1986). Significant contamination with Staphylococcus aureus can occur even though Staphylococcus aureus is not detected in the intestinal tract. This contaminationÂ comes from sources other than the bird and the contaminating strains also appear to be endemic to the processing plant (Notermans et al., 1982). Washing of carcases after evisceration and before chilling removes organic matter and some of the micro-organisms acquired during evisceration. The visceral cavities also become contaminated during evisceration, especially when the intestines are cut and it is less easily reached by washing with conventional washing equipment (Notermans et al., 1980; Mead, 1982; Connor et al., 1987; Jones et al., 1991). However, strategically sited spray-washers with high-pressure and the use of water containing at least 40ppm available chlorine are effective in reducing the number of bacteria and 70ppm chlorine almost totally eliminated build-up of bacteria (Notermans et al., 1980; Bailey et al., 1987; Mead, 1989).
In many processing plants, the rate of processing is such that there is little loss of heat from the carcases before if reaches the chilling stage. The deep muscle temperature of the freshly eviscerated carcases is “30°C and to prevent and limit the growth of spoilage bacteria and pathogens it is necessary that the carcases must be chilled rapidly and efficiently after evisceration to a keep temperature of below 10°C (McMeekin et al.a, 1979; Eustace, 1981; Mead, 1989). Two methods of chilling are in common use, one involving dry chilling in cold air and the other immersion of carcases in ice-chilled water (Mead, 1982; Mead, 1989). Continuous immersion chilling is the most widely used method and comprises one or more units, each consisting of a large tank capable of holding many hundreds of carcases, through which water flows continuously. The water can flow with or against the direction taken by the carcases (Bryan, 1980; Mead, 1982). In through-flow systems carcases move in the same direction as the water flow, whereas in counter-flow chillers the birds are moved mechanically in the opposite direction to the flow of in-coming water (Mead, 1982). Hygienic operation of immersion chillers requires measures to prevent a build-up of microbial contaminants in the cooling medium and this depends on the water usage and temperature control. Adequate use of fresh water aids the cooling process and prevents the chiller temperature from reaching a point when bacterial growth becomes a problem (Mead, 1989). The water temperature at the carcase entry and exit points must not exceed 16°C and 4°C respectively (Mead, 1982). Counter-flow immersion chilling (in which carcases at the end of the chilling process come into contact with the cleanest water) effectively decreases counts on carcases and minimises cross-contamination (Bryan, 1980). Air-chilling, whether as a batch process in a chill room or by continuous air-blast, requires the use of low scald temperatures of ca. 50°C. This is to avoid skin damage and colour change of the carcases (Bryan, 1980; Mead, 1989). Air-chilled carcases are always likely to have higher bacterial counts than those chilled in properly controlled immersion systems. Several studies have confirmed this supposition, although the
Bacterial counts can increase after chilling, because of the transfer of micro-organisms during weighing and packaging. Even at this stage contamination with salmonellas can occur and therefore, the final product should be frozen or transferred to a chill store without delay (Bryan, 1980; Mead, 1989).
Materials and Methods
Laboratory evaluation (Anolyte): Anolyte for minimum inhibitory concentration (MIC) determinations under laboratory conditions was supplied by Radical Waters. The MIC was determined on the same day the Anolyte solution was obtained.
Poultry Plant evaluation (Anolyte): Fresh Anolyte solution was prepared on the day of evaluation for a particular application.
Catholyte evaluation during scalding: Catholyte was supplied by Radical Waters, for evaluation during scalding. NOTE: 0,01 % Sodium thioglycolate was added to all test solutions to neutralize the anolyte, before conducting microbiological analysis.
Applications, sample collection and preparation
Applications and sample collection
For each of the above applications, control samples of chickens were randomly taken off the processing line.
A composite meat and skin sample was prepared, by taking samples from the neck, back between the wings and under the wing 5g of sample was added to 45 ml of sterile Ringers solution to give a 1:10 dilution. From this a dilution series (10-¹ – 10-6) was prepared for plating.
This composite sample was placed into quarter strength Ringers solution in a 1+9 mass/volume ratio based on exact mass. Each composite sample was homogenised for 20 min (Seward Medical 400 Stomacher Lab Blender). Tenfold serial dilution’s in Ringers solution were plated out in duplicate on Nutrient Agar for the total bacteria count and on McConkey agar for the coliform bacteria count, using the spread-plate technique (ICMSF, 1978; Busta et al., 1984; von Holy et al., 1992) and incubated aerobically at 37°C for 48 h. Plates showing between 30 and 300 colony forming units (cfu) (or the highest number if below 30) were counted. Bacterial counts obtained from the plates of each duplicate set were meaned.
During the laboratory evaluation of the anolyte solution, a 1:10 dilution gave the best result, using E.coli as test organism. The 1:20 and lower dilutions, did not result in a significant decrease of E.coli, using ca. 106 organisms as a challenge. Hence, it was decided to use the 1:10 dilution in our evaluation. The anolyte spray compared very favourably with the current practise in all applications. The most promising result was obtained immediately after defeathering, where the anolyte resulted in a significant decrease in the bacterial numbers compared to the control. It is highly recommended that this practise be followed, since it will reduce the bacterial numbers right at the outset and very early on during processing. Both the post-eviration spray application and the spinchiller application compared favorably with the current practice. Catholyte used during the scalding application, did not result in an improved result, with regards to the bacterial numbers on the skin, nor on the feathers. It should also be noted, that should the catholyte disperse the bacteria during scalding, without also killing the bacteria, it might result in a higher level of contamination, because bacteria attached to the feather will be dispersed, which may not be case with the current practise.
It was concluded, that the anolyte solution (1:10 dilution) could replace the current practise and especially if it is introduced directly after defeathering it could have major benefits. The use of catholyte during the scalding application is not recommended.