Contamination in the food chain and its control
Food can pick up physical, chemical and biological hazards at any step from farm to fork. Control means keep clean, separate, cook, chill and use safe water and raw materials.
Key terms
Contamination is the presence of any harmful or unwanted substance or organism in food. A food hazard is a biological, chemical or physical agent in food that can cause illness or injury. Food safety means the food will not harm the person who eats it when it is prepared and eaten as intended. The food chain is every step food passes through: farm, harvest and storage, processing, transport and market, kitchen and plate, often called farm to fork. Contamination can be direct (rat droppings fall into stored grain) or by cross-contamination, where germs or harmful matter move from one food, surface or person to another: raw chicken juice dripping onto cut salad, or one knife used for raw meat and then for cooked food.
The three types of food hazards
| Hazard | What it is | Common sources | Indian examples |
|---|---|---|---|
| Physical | Hard, sharp or unwanted foreign objects | Field stones and soil, broken glass, loose metal from machines, packaging bits, jewellery, hair, nails | Stones in rice, dal and rava; glass bangle pieces; hair in hotel food; stapler pins from packets |
| Chemical | Harmful substances, natural or added | Pesticide residues, cleaning chemicals, toxic metals, non-permitted colours, excess additives, natural toxins, chemicals leaching from packaging | Pesticide residues on vegetables; lead chromate on turmeric; metanil yellow in dal; floor cleaner stored next to cooking oil; aflatoxin in mouldy groundnuts |
| Biological | Living organisms or the toxins they make | Bacteria, viruses, parasites and moulds from soil, unsafe water, sewage, raw meat, food handlers and pests | Salmonella in eggs and chicken; Staphylococcus aureus from a handler's boil into sweets; typhoid, cholera and hepatitis A from unsafe water in street foods; tapeworm in undercooked pork |
Hazards from farm to fork
Each step can add a hazard, so each step needs its own control.
Factors that contribute to contamination
- Poor personal hygiene: unwashed hands, sick food handlers, coughing or sneezing over food.
- Temperature abuse: cooked food left in the danger zone (5-60 °C) for hours, slow cooling of large pots of rice or sambar, food reheated only till warm.
- Cross-contamination: raw and cooked food stored, cut or handled together.
- Unsafe water and raw materials: sewage-irrigated vegetables, cracked eggs, loose unlabelled spices and oils.
- Pests: rats, cockroaches and flies carry germs on their bodies and in their droppings.
- Poor cleaning and building design: dirty equipment, cracked surfaces, open drains, no separate raw and cooked areas.
- Chemical misuse: spraying pesticide close to harvest, storing cleaners in old food containers, wrapping food in newspaper.
- Deliberate adulteration for profit, covered later in this unit.
Prevention and control of food-borne hazards
| Hazard | Prevent it (good practices) | Control it (checks and systems) |
|---|---|---|
| Physical | Buy cleaned grain from reliable suppliers; sieve and pick rice, dal and rava; cover hair; no jewellery at work; glass and brittle-plastic policy; maintain machines | Sieves, magnets and metal detectors on processing lines; visual inspection; pest-proofing |
| Chemical | Use only permitted additives within limits; keep cleaners labelled and stored away from food; food-grade containers; wash produce; respect the waiting period after pesticide spraying | Supplier certificates, testing of raw materials, a chemical register, staff training |
| Biological | WHO Five Keys to Safer Food: keep clean; separate raw and cooked; cook thoroughly (centre at least 70 °C); keep food at safe temperatures (hot above 60 °C, cold below 5 °C, not more than 2 hours at room temperature); use safe water and raw materials | Temperature records, cleaning schedules, health checks of handlers, pest control, HACCP critical control points |
In a hospital kitchen one slip can harm patients whose immunity is already low, so raw and cooked areas, boards and staff are kept apart. In a school mid-day meal kitchen, picking stones from rice and dal and serving food hot are two of the simplest, most useful controls.
2 marks: “What is cross-contamination?” Transfer of harmful microbes or substances from one food, surface or person to another, e.g. raw chicken juice dripping onto cut salad, or one knife used for raw meat and cooked food.
5 marks: “Explain physical, chemical and biological hazards in food with examples.” Define a food hazard; one paragraph on each type with two or three Indian examples; end each with one prevention line.
10 marks: “Discuss the factors contributing to contamination in the food chain and the measures to prevent food-borne hazards.” Define contamination and the food chain; draw the farm-to-fork flow; three hazard types with sources; list the factors (hygiene, temperature, cross-contamination, water, pests, chemicals); prevention table by hazard; WHO Five Keys; close with GMP and HACCP.
Three hazards are P-C-B: Pebbles (physical), Chemicals, Bugs (biological). WHO's Five Keys: clean, separate, cook, safe temperatures, safe water and raw materials.