Contamination
Live tissue in animals is essentially sterile with but it is during food preparation that it can become contaminated at any stage of the process. The most critical stages are skinning and evisceration as it is the hide and the intestines that contain the animal’s micro-flora along with organisms present in faeces and soil. Abattoir hygiene must be kept to a very high standard to prevent contamination from faecal matter and other carcasses. E-Coli is the most commonly associated organism although this causes a food borne infection which depending on the text book is sometimes classes separately from food poisoning. Raw or undercooked beef and minced beef are cited as the main sources of human infection.
Temperature
Temperature of both raw and cooked food must be regularly checked to prevent microbial growth. Food that is being reheated must be reheated to a temperature of approx 70oC to ensure any organisms growing are destroyed prior to consumption. Undercooking is another common cause of food poisoning, especially with poultry. The most common food poisoning organism Campylobacter Jejuni is most often associated with undercooked chicken. Birds have been recorded with heavy contamination – 2.4x107 has been recorded (Garbutt 1997)
Re-Contamination
Once food is cooked and all organisms have been removed it is possible that the food may be re-contaminated from raw products. In any place food is prepared there is a strict colour coding for raw and cooked meat to ensure cross contamination is prevented.
Ingestion of Raw Foods
Eating raw or improperly cooked food can result in food poisoning due to viral infection. One example of this is shellfish harvested in polluted waters. Bivalve molluscs can filter and concentrate virus particles as well as bacteria in the gut, as shellfish are eaten whole the gut plus all the virus particles are ingested along with the rest of the animal. A remedy is to hold the shellfish in a tank with sterilized water using ultraviolet light to destroy any viruses although some enteric viruses may remain.
Contamination of Raw Materials
Contamination of raw materials with pathogens is a widespread problem contributing to food poisoning. Most wild and farm/domestic animals carry pathogenic organisms in their gut which are all transmissible to man. There are several factors which seem to make the problems worse including intensive farming where organisms are spread via the faecal-oral route, transport of animals in overcrowded conditions and the use of concentrated animal feeds that become infected with pathogens.
Heat Process Failure
Heat Process failure can occur in products such as Milk. The pasteurization process kills the organisms that cause spoilage in raw milk however recontamination can occur due to the presence of organisms such as Streptococcus Thermophilus which are resistant to high temperatures. If steps such as aseptic packaging are taken to prevent contamination spoilage may still occur caused by organisms such as Bacillus Circulans which have also survived the heat process and produce a bitter-sweet flavour due to coagulation of the milk protein caused by rennin-type enzymes.
Post process recontamination
Post process recontamination occurs when food is cooked slowly in large quantities and then left to stand for a long time at room temperature. The most common associated organism is Clostridium Perfringens which is found in most soils mud and consequently dust. Most outbreaks are associated with meat, mainly beef, which has been boiled, stewed, or casseroled and then held at room temperature or in bulk in refrigerators where cooling is slow. Prevention can be promoted by cooling rapidly to 7oC and ensure reheating reaches a temperature of over 70oC.
None or inadequate refrigeration
None or inadequate refrigeration will allow organisms to multiply leading to toxic levels in food. Foods should be stored at 5oC or less but preferably 0-3oC while the preparation area should be between 12-14oC to minimise multiplication. For example rice naturally contains Bacillus Cereus which is a spore forming organism not destroyed by cooking, the legal requirement is for rice to be stored at 68oC or higher or 8oC or lower. It must also be brought to refrigeration temperature quickly and not reheated more than once to prevent the spores producing a heat stable enterotoxin which causes nausea and vomiting.
Staff Hygiene
Poor personal hygiene can contribute to food poisoning outbreaks, for example staff not washing their hands at all/effectively after using to toilet or coughing/sneezing. The natural habitat of Staphylococcus Aureus is the human nose, throat and skin so to prevent contamination anyone with cold/flu like symptoms must be excluded from the food handling or processing area. Another problem with personal hygiene is the presence of ‘Carriers’ working in food industry. These people are asymptomatic but still infected, most commonly with Salmonella and E-Coli. A carrier may remain infected for weeks, sometimes months.
Pests
Pests such as flies, cockroaches, mice, rats and birds all carry food poisoning organism. Careful effort must be made to ensure any food storage or preparation area is pest free. Methods of prevention can include rodent traps and UV fly killers. Salmonella is naturally found in the intestine of most animals, domestic or wild, including mammals, birds and insects. It is excreted in large numbers in faeces and can remain viable for years within the faecal material.
Bibliography
Essentials of Food Microbiology
John Garbutt, Arnold (1997)
Human Nutrition – A Health Perspective
Mary. E. Barasi 2003 – Arnold (2003)
Human Nutrition and Dietetics
Garrow, James & Ralph – Churchill Livingstone (2004)
www.food.gov.uk
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