Know your enemy
Foods that are commonly contaminated include poultry, eggs, milk, seafood and dairy products.
The testing of food contaminants can be done from “farm to fork”, for example, before the food is processed, at the semi-processed stage, after chilling, before packing, and even before the food is released to the market.
Some of the common food contaminatants are Salmonella, Campylobacter, E. coli, Listeria monocytogenes, Staphylococcus aureus and Bacillus cereus.
Bacterial toxins can also contaminate food. These include Staphylococcal aureus enterotoxins, Bacillus cereus toxin or C. botulinum toxins.
Contamination by viruses can also occur. Examples include noroviruses and the hepatitis A and E viruses.
Some parasites, such as toxoplasma, trichinella, anisakis and giardia, may be present in different types of food (especially meat and fish products).
Contamination may occur at various levels. Primary contamination can occur during the production of raw materials (at slaughter, fishing or during milking).
Secondary contamination occurs during the processing of raw materials, such as during cutting and grinding of meat, the addition of ingredients and packaging of products, or during the production and ripening of cheeses, or during evisceration, cutting, salting and packaging of fishery products.
Contamination can also occur during transport and marketing of food. This is called tertiary contamination.
Quaternary contamination refers to contamination during the preparation of food, such as in kitchens and canteens. In kitchens, so-called cross-contamination occurs frequently, i.e. the transfer of bacteria or viruses from a contaminated product to a healthy one due to the use of contaminated instruments (cutting boards, knives, pans, dirty hands, dirty gloves, etc).
It is very difficult to distinguish contaminated food from healthy food, unless you run laboratory tests. Food that is contaminated with pathogenic bacteria does not exhibit any particular appearance that indicates it is contaminated.
What you can do is pay attention and prevent opening cans that appear swollen, which could be due to gas production by spore-forming bacteria that have survived heat treatments, such as Clostridium botulinum. Its toxins are very dangerous to humans, causing botulism (a serious disease characterised by progressive paralysis and even death).
When a certain food has altered its organoleptic characteristics (bad smell, abnormal colour, softening), it is usually contaminated with non-pathogenic spoilage bacteria, such as fresh meat altered by psychotropic Pseudomonas and other bacteria that are able to grow at refrigeration temperatures.
Top 10 tips for food safety
1. Storing raw food
Separate raw foods from cooked foods and store them at refrigeration temperature. You should also separate raw meat, fish and eggs in shell and vegetables.
Refrigerate foods quickly because cold temperatures keep most harmful bacteria from multiplying.
If you accidentally break an egg, don’t keep it in the fridge to be used later.
2. Storing cooked food
Cooked food should be protected from external contamination by wrapping or covering it. Plastic or metal containers, or bowls with lids, are fine.
Cooked foods should not be stored at high temperatures (e.g. room temperature) unless they are consumed very quickly (maximum within half an hour).
They should be stored at low temperature and then eventually re-heated before consumption.
Alternatively, cooked products to be consumed warm can be stored at more than 60°C.
It is very dangerous to store cooked food at 40°C, as many caterers do, because this temperature allows bacteria to grow very quickly.
Defrost frozen foods at refrigeration temperatures and not at room temperature as some pathogenic bacteria in food can double their number, even at low temperatures. The more bacteria there is, the greater the chances of one becoming sick from eating the food.
4. Wash your hands and utensils
Wash your hands before preparing food and always use clean utensils such as cutting boards, plates, knives, kitchen scissors, forks, spoons and containers.
5. Do not cross-contaminate
Do not use tools or utensils used to prepare raw foods such as meat, fish, and vegetables to prepare cooked food. This increases the risk of cross-contamination of a cooked product, which favours bacterial growth as it is without its own competitive flora.
When handling raw meat, poultry, seafood and eggs, keep these foods and their juices away from ready-to-eat foods.
6. Shelf life
Eat food during its shelf-life – before the “use by” date or the “best before” date. Never buy too much food with a long shelf-life and never buy food too close to its “use by” date.
7. Raw food
Cook raw meat and raw fish at proper temperatures (minimum 70°C for meat). Boil raw milk (and that includes goat or cow’s milk that is delivered to your home).
8. Wash your food
Wash fruits and vegetables before eating; if you cannot peel them, disinfect with chlorinated products.
9. Dispose properly
Waste disposal of meat, vegetables, and raw fish must be carried out immediately in the appropriate containers, both in the kitchens of restaurants and in domestic kitchens. Even leftover cooked products that are no longer used must be disposed of quickly to prevent bacteria growing.
10. Clean – Separate – Cook – Chill
These are the four key words for food safety.