9 min readConcept sheetIrradiation is often a 10-mark answer; smoking is a 5-mark note

Smoking and irradiation

Smoking preserves by drying, heat and antimicrobial smoke chemicals. Irradiation exposes food to gamma rays or electron beams that damage microbial DNA without heating the food.

Smoke chemicalsPhenols, formaldehyde, organic acids, carbonyls

Dose unitGray (Gy): 1 joule absorbed per kg; 1 kGy = 1000 Gy

SourcesCobalt-60 gamma rays (most used), caesium-137, electron beams, X-rays

LabelRadura logo with words saying the food is irradiated

Smoking

Smoking exposes food, usually salted first, to smoke from slowly burning hardwood or sawdust. It preserves by (1) drying the surface, (2) antimicrobial chemicals in the smoke such as phenols, formaldehyde and acetic and other acids, (3) antioxidant phenols that slow rancidity and (4) in hot smoking, heat that kills many microbes. It also adds flavour and a brown colour. Cold smoking (below about 30 °C) flavours without cooking (fish, cheese) and needs salting or chilling as well; hot smoking (about 60-80 °C) cooks the food (ham, sausages, fish). Liquid smoke, smoke condensed into water, is a cleaner modern option. In Northeast India, pork, beef and fish are traditionally smoked over the kitchen hearth.

Advantages and limitations of smoking

AdvantagesAdds flavour and colour; drying, antimicrobial and antioxidant effects together lengthen keeping time; simple and traditional; suits meat, fish and cheese.

LimitationsWorks mainly on the surface; alone it gives limited shelf life; smoke contains polycyclic aromatic hydrocarbons (PAHs) such as benzo(a)pyrene, which can cause cancer, so heavy, frequent intake is unwise; uneven results; fire risk.

Irradiation: principle

Food irradiation exposes food to ionising radiation: gamma rays from cobalt-60 (most used) or caesium-137, electron beams or X-rays. The rays damage the DNA of microbes, insects and sprouting buds, directly and through free radicals formed from water, so they cannot multiply. At the energies allowed the food is not made radioactive and is barely heated, so irradiation is a 'cold' process, and it can treat food already packed. Dose is measured in gray (Gy): 1 Gy = 1 joule absorbed per kg; 1 kGy = 1000 Gy. A joint FAO/IAEA/WHO expert committee concluded in 1980 that food irradiated up to an overall average dose of 10 kGy raises no toxicological hazard. Irradiated food must carry the Radura logo.

Doses and uses of irradiation

Dose level	Purpose	Examples
Low (up to 1 kGy)	Stop sprouting; kill or sterilise insects; delay ripening	Onion, potato, garlic, ginger; cereals, pulses, dried fish; mango and banana; Indian mangoes exported to some countries are irradiated for quarantine; BARC's KRUSHAK unit at Lasalgaon, near Nashik, treats onions
Medium (1-10 kGy)	Radurisation: cut spoilage microbes to extend shelf life. Radicidation: kill non-spore-forming pathogens such as Salmonella	Fish, meat, poultry, fresh fruits; spices and frozen prawns
High (above 10 kGy)	Radappertisation: sterilise (with blanching to stop enzymes)	Meals for astronauts and immune-compromised hospital patients

Advantages and limitations of irradiation

AdvantagesNo heating, so fresh-like quality; treats packed food, so no recontamination; no chemical residue; deep penetration; replaces chemical fumigants for insects in grains and spices; cuts storage losses of onion and potato.

LimitationsCostly plants with strict radiation safety and licensing; consumer fear; some loss of thiamine and vitamin E; off-flavours in fatty foods and milk at higher doses; does not destroy toxins or reliably inactivate viruses, and cannot make spoiled food good; spores need very high doses; must be labelled.

In food and nutrition

Irradiation makes spices, dried fish and frozen prawns safer from Salmonella and lets hospital kitchens serve sterile meals to immune-compromised patients; nutrient losses are similar to or smaller than in cooking. Smoked foods are best eaten only occasionally because of PAHs.

Exam angle

2 marks: “What is the Radura?” The international logo that must appear on irradiated food, with words stating that the food has been treated by irradiation.

5 marks: “Write a note on preservation by smoking.” Process (hardwood smoke, salting first); how it preserves (drying, phenols, formaldehyde, acids, antioxidants, heat); cold vs hot smoking; liquid smoke; PAH concern; examples.

10 marks: “Explain the principle and applications of food irradiation.” Ionising radiation, sources, DNA damage, cold process, gray unit; low, medium and high doses with uses; Radura labelling; advantages and limitations; Indian examples.

Remember it

Doses: below 1 kGy stops sprouts and bugs; 1-10 kGy cuts microbes; above 10 kGy sterilises. Radurisation (shelf life) → radicidation (pathogens) → radappertisation (sterile).