Poultry Slaughter and Dressing
5.6. Meat Decontamination
Introduction
Total prevention of microbial contamination on carcasses during slaughter and dressing, even when using the best available techniques and methods, is not achievable. Although most of the microflora on carcasses are spoilage organisms, food-borne pathogens also occur. Intervention measures to reduce the numbers of pathogenic bacteria on carcasses may be employed at various stages in the meat chain, including final carcass decontamination at the end of the slaughterline. Presently, meat decontamination is not practised in the EU; the main reasons include concerns that operators may lower hygiene standards if they rely on final decontamination treatments.
Currently in the EU, the only method allowed for decontamination of carcasses at slaughter is hot water; steam condensation and hot water may be authorized by the Official Veterinary Surgeon. However, in the USA, decontamination treatment at the slaughterline is mandatory.
Non-chemical decontamination treatments
The effectiveness of some non-chemical treatments is indicated in Table 5.5.
Steam Pasteurization System™
With this system, steam (105°C) is used to pasteurize the external surfaces of the carcass. The steam condenses on carcass surfaces at temperatures between 80°C and 85°C, causing only temporary deleterious colour changes from red to grey–brown. However, the carcass recovers normal red colour after chilling. The carcass surface temperature is critical, since temperatures of >85°C cause permanent discolouration, i.e. the grey–brown colour of cooked meat. However, temperatures <80°C are insufficiently effective in killing microorgnisms. Reductions of 2.5 to 3.7 logs of pathogenic bacteria (e.g. L. monocytogenes, E. coli O157, Salmonella) have been reported for steam pasteurization. Therefore, high numbers of bacterial pathogens cannot be totally eliminated using this procedure.
Instead of steam, hot water treatments can be used, with a similar temperature window.
Irradiation
Irradiation is currently used in the USA, primarily for minced meats and poultry, which have greater public health risks. Effective doses range from 1 to 3 kGy, but irradiation at higher doses can cause sensory (particularly colour) changes in the meat. The types of irradiation used for meat decontamination (gamma rays, X-rays) do not induce secondary radiation
Table 5.5. Effectiveness of non-chemical treatments.
Examples of bacterial reduction (log) on
Treatment meat achieved
Spot-cleaning (steam/hot water vacuuming) Total bacterial count 1.7–2.0, coliforms 1.7–2.2 Combination of knife trimming and water Total bacterial count 1.0–1.8, E. colicount spray washing (28–42°C) 1.0–1.6, coliforms 1.6
Hot water (74–83.5°C) Total bacterial count 0.66–2.00, E. coli/coliform count 1.8–3.0;
pathogens (Salmonella,E. coliO157,Yersinia, L. monocytogenes) 3.0
Pressurized steam on chickens Total bacterial count 1.0–3.0, Salmonellaby 50%
(180–200°C)
Steam Pasteurization SystemTM Pathogens (L. monocytogenes,E. coliO157,
(105°C) Salmonella) 2.5–3.7, total bacterial
count/coliforms 1.4 Multiple hurdle decontamination E. coli4.3
Effects of high-temperature treatments (i) Generally, temperatures >80°C but <85°C
on meat quality cause bleached, grey or ‘cooked’ meat
appearance, to approximate depth of 0.5 mm. However, this is usually unnoticed after a few hours of chilling.
(ii) Exposure to temperatures >85°C causes permanent damage to surface bloom Irradiation: poultry Salmonella3,Campylobacter>3 (frozen 3–5 kGy; chilled 1.5–2.5 kGy)
Irradiation: eggs Salmonella7–8, total bacterial count 6 (4–5 kGy)
Irradiation: red meat Salmonella2–3
(1–3 kGy)
Limitations of irradiation Does not inactivate viruses or microbial toxins, causes sensory changes at higher doses
Ultrasound Salmonella<1–4
(in liquid substrates)
Electromagnetic radiation (i) Microwave: Salmonella1–2
(in various substrates or on meat) (ii) Visible light: total bacterial count 1–3 (iii) Ultra-violet: Salmonella,Staphylococcus,
Yersinia,Campylobacter0.4–3.0 Electricity (high-voltage pulsed electric field) In fluid foods: Staphylococcus aureus,E. coli
up to 6
High pressure At 400–450 MNm⫺2: total bacterial count 3–5
in the product (the meat does not become radioactive), although this is frequently a concern in consumer acceptance tests. Pathogen reductions of 2 to 3 logs for Salmonella have been obtained. However, irradiation does not inactivate viruses or pre-formed microbial toxins. On the other hand,
there are concerns that irradiation may enhance fat oxidation, contributing to formation of potentially toxic free radicals, believed to be carcinogenic compounds.
Electricity (high-voltage pulsed field)
Application is limited to liquid foods, in which Staphylococcus aureusandE.
coli O157 reductions of up to 6 logs were achieved. However, this method is largely experimental.
High pressure
Pressure at 400 to 450 MN/m2has been used in experimental conditions to reduce total bacterial counts by 3 to 5 logs. This technique would be largely restricted to liquid foods.
Chemical decontamination treatments
The effectivenes and feasibility of some chemical treatments are summarized in Table 5.6.
Acid treatments (lactic, acetic, citric, fumaric)
Weak organic acids, which are used in other areas of food processing, are normally used for acid treatments of carcasses. Salts of organic acids have only bacteriostatic effects, and do not kill bacteria to a significant extent. Acid treatments of red meat carcasses are common in the USA, and reductions of up to 4.5 logs have been reported, e.g. for Yersinia.
However, acid treatments were found to be less effective against the more common meat-borne pathogenic bacteria including Salmonellaand E.coliO157.
The antimicrobial effectiveness of acid treatments depends on numerous factors, including characteristics of the acid itself and the characteristics of the target microorganism(s). Acids are less effective against mesophillic pathogens, but can be more effective against psychrotrophs. At the time of slaughter, most of the microbial load on carcasses is comprised of mesophillic bacteria. Some pathogens appear to be more acid resistant (e.g. E. coli O157 and Listeria) than others.
If not all pathogens are killed, due to differences in sensitivity between and within bacterial species, meat decontamination could result in the selection of highly resistant strains. This could potentially increase problems with their control during subsequent meat preservation/
processing stages.
Technical aspects of the acid used must be also considered. These include the issue of their impact on the environment, unless they are suitably treated before disposal.
Acid treatments could also have deleterious effects on meat quality. Fat discolouration, lean bleaching and alterations in flavour and odour can occur. The water-holding (drip) characteristics can also be altered. In addition, the negative effects on meat quality can actually shorten product shelf life, instead of its expected lengthening.
Non-acidic chemical treatments
Non-acidic chemicals currently in commercial use are chlorine and trisodium phosphate. Chlorine was previously widely used in the UK poultry industry (reductions of Salmonellaby 1.5 logs), but has been banned due to its possible reactions which can result in potentially carcinogenic compounds.
Trisodium phosphate is in current commercial use, and achieved pathogen reductions range roughly between 1 and 2 logs.
Table 5.6. Factors affecting feasibility and effectiveness of chemical treatments.
Consideration of factors Examples of bacterial
affecting antimicrobial reduction (log) on meat
efficacy Practical considerations achieved
Acid characteristics Technical aspects Acids (lactic, acetic, citric, Concentration required Method of application fumaric)
Solubility Contact time required Salmonella: 0.4–2.0 Dissociation at meat pH Temperature E. coliO157: 0.3–2.0 Ability to penetrate the Pressure Listeria: up to 2
bacterial cell Target tissue Yersinia: up to 4.5 Intracellular action characteristics Aeromonas: up to 3.5 Specific reactions Impact on the
with meat compounds environment/equipment Salts of organic acids
Toxicity/residues Recycling/neutralization Bacteriostatic effects
(GRAS or additive) Staff health only
Costs
Characteristics of target Consumer attitude Non-acid chemicals
organism(s) Chlorine: Salmonella1.5,
Psychrotrophic or Meat quality aspects E. coliO157 1.3 mesophyllic nature Fat discolouration Trisodium phosphate:
Some pathogens Lean bleaching Salmonella0.9,E. coliO157 particularly resistant Change of flavour/odour 1.4, Listeria1,
(E. coli O157,Listeria) Water-holding (drip) Staphylococcus1 Initial microbial load Sensory scores Hydrogen peroxide: total Intra-species Meat shelf life bacterial count 1–3
strain/clonal selection Ozone solution: total
Enhanced regrowth in bacterial counts: 1.0–2.9
absence of competitors Animal dehairing by sodium
Stress-mediated sulphide/H2O2:
resistance to subsequent E.coliO157 3,
treatments Salmonella3,Listeria3,
Change of virulence total bacterial count 1.0–1.5
Overall considerations
Because carcasses are often contaminated with food-borne pathogens even under best hygiene conditions in commercial abattoirs, decontamination treatments may be beneficial for meat safety. However, presently available treatments only proportionally reduce the microbial load, which raises questions about positive selection for toughest microbial strains in the surviving populations. Obviously, meat decontamination should not be considered as a substitute for good overall process hygiene: the cleaner the carcass the better the decontamination effects. The role of final carcass decontamination in meat safety systems should be considered simultaneously with some other alternative or additional approaches, such as pre-skinning hide decontamination.
Further Reading
Anon. (1998) Opinion of the Scientific Committee on Veterinary Measures Relating to Public Health on Benefits and Limitations of Antimicrobial Treatments for Poultry Carcasses. European Commission, Consumer Health and Protection Directorate-General, Brussels.
Farkas, J. (1998) Irradiation as a method for decontaminating food. A Review. International Journal of Food Microbiology44, 189–206.
James, C. (1999) Past, present and future methods of meat decontamination: update 1999.
MAFF Fellowship in Food Process Engineering,University of Bristol, UK.
James, C., Goksoy, E.O. and James, S.J. (1997) Past, present and future methods of meat decontamination. MAFF Fellowship in Food Process Engineering,University of Bristol, UK.
Smulders, F.J.M. and Greer, G.G. (1998) Integrating microbial decontamination with organic acids in HACCP programmes for muscle foods: prospects and controversies.
International Journal of Food Microbiology44, 149–169.