VMBO Year 2 · HAVO/VWO Years 2–3 · Nutrition and digestion · Section 2.5

Food spoilage

Foodborne illness

Food can spoil when bacteria and fungi grow on it. Foodborne illness can result from eating food containing harmful microorganisms or their toxins. Unsafe food does not always look or smell different.

Salmonella bacteria may occur in raw poultry, pork, eggs and other foods, including contaminated fruit and vegetables. Warm conditions can allow bacteria to multiply quickly.

Salmonella infection can cause diarrhoea, fever and abdominal pain. Symptoms often begin within a few days, but timing and duration vary. Foodborne illness is not simply an immune reaction to spoiled food.

Preserving food

Food preservation slows spoilage by making conditions less favourable for microorganisms, reducing their numbers or preventing contamination. Methods include:

• Freezing: Keeping food at a sufficiently low temperature, typically around −18 °C or colder, stops most microorganisms multiplying but does not reliably kill them. Safe thawing, storage and refreezing depend on the food and how it has been handled.
• Pasteurisation: Controlled heating, for example milk at about 72 °C for a short time, reduces harmful microorganisms. It does not sterilise food, so storage instructions still matter.
• Sterilisation: A suitable heat treatment makes packaged food commercially sterile. Different foods require different processes; UHT treatment of milk uses very high temperatures for a short time and sterile packaging.
• Vacuum packaging: Removing much of the air slows some spoilage processes. It does not stop every microorganism: some grow without oxygen. Vacuum-packed foods may still need refrigeration.
• Modified-atmosphere packaging: Replacing air with a controlled gas mixture, such as carbon dioxide, nitrogen and sometimes oxygen, can extend shelf life and help maintain appearance.
• Drying: Removing enough available water inhibits microbial growth, as in milk powder and raisins.
• Adding preservatives: Salt, sugar or acid can reduce microbial growth, as in jam or pickled foods. Approved preservatives such as sulphites may also be added.
• Irradiation: Approved ionising radiation treatments reduce some microorganisms or pests. Irradiated food does not become radioactive. Permitted uses depend on food regulations.

Additives

Food additives are substances added for functions such as preservation, colour or flavour. Some come from natural sources, such as beetroot colouring; others are manufactured.

Whether a substance is natural or synthetic does not by itself determine its safety. Labels identify ingredients and relevant additives.