Irradiation

Why do we preserve food?

• Protect people from microorganisms, parasites, and other pests

• Extend shelf-life, improve long-term quality

• Make desirable alterations to food properties

History of Food Preservation

Oldest Methods- Drying

- Fermenting

- Salting

- Smoking

Newer Methods- Freezing- Canning- Refrigeration- Preservatives- Pesticides

Newest Method: Irradiation

What is food irradiation?

Ionizing Radiation

• Radiation that has the ability to produce ions - electrically charged particles

• Examples: alpha particle, beta particle, high energy electron, gamma ray, and x-ray

• X-ray – are penetrating electromagnetic waves. Produced by bombardment of a heavy metal target with cathode rays within evacuated tube. Not economical to use in food industry.

• Gemma rays – good penetration. Upto 20 cm in most foods. Emitted from by products of atomic fission. Cobalt 60 and cesium 137 is mosty used as the source.

• Beta rays – stream of electrons. Higher the charge deeper the penetration.

• Cathode rays – poor penetration, 0.5 cm. However, greater effeciency than gemma rays, made to hit the food. stream of electrons from cathode of an evacuated tube. Electrons are accelerated by artificial means.more safer than gemma rays.

Nonionizing Radiation

• Does not have sufficient energy to create ions - instead tends to excite molecules without removing electrons

• Examples: UV, visible light, television waves, radio waves, and microwaves

Ultraviolet irradiations• Most widely used in food industry

• Wavelengths near 260nm is strongly absorbed by purines and pyrimidines and is therefore the most germicidal.

• Uv around 200 nm is strongly absorbed by the oxygen and therefore may produce OZONE.

• Uv source in food industry is quartz mercury vapor lamp. Ehich emit radiation at 254 nm.

Sources of Ionizing Radiation

• Cosmic Radiation (the sun)

• Medical procedures• Radon and other

terrestrial sources• Nuclear weapons

fallout

• Power plants• Fertilizers• Smoke detectors• Accelerators

Food Irradiator Sources

• Cobalt-60 and Cesium-137– Emit gamma rays– Sealed in container - never touches food– Can be recycled

• Machine generated beta or x-rays– Produces no waste outside of the machine used

to produce the radiation

Factors influencing effectiveness

• 1. Time – longer time, more effective the treatment.

• 2.Intensity- intensity will depend on the power of lamp, distance from the lamp, and interfernece inthe way of rays.

• 3. Penetration – nature of the material being irradiated, dissolved mineral salts,especially of iron.

• Even thin layer of fatty or greasy material cuts off the rays.

• Therefore mostly rays affect the outer surface of most irradiated foods directly exposed to lamp.

Application in food inductry• Treatment of water used for beverages.

• Treatment of knives for slicing bread

• Packaging

• Sanitizing of eating utensils..

• Prevention of yeast on pickle, vinegar

• Killing of spores on sugar crystals and syrups

• Aging of meat

• Prevention of mold growth on walls in production area.

• Treatment of air.

Irradiation Processes

• Sterilization

• Pasteurization

• Disinfestation

• Sprout Inhibition

• Delay of Ripening

• Physical Improvements

Irradiation Sterilization

• Very high dose used to kill all organisms

• Sterilization of > 50% disposable

medical instruments

• Food sterilization - NASA, military,

transplant patients

Irradiation Pasteurization

• Reduces remaining number of living

organisms

• Prevent growth of mold

• Kill bacteria and parasites

Irradiation Disinfestation

• Kills insects and parasites in grains and

other stored foods

• Fewer chemical residues on fruits and

vegetables

• Does not prevent against re-infestation

Physical Improvements

• Inhibit sprouting of potatoes, onions, and garlic

• Delay of ripening for strawberries, mangoes, bananas, tomatoes, etc.

• Incidental improvement in fruit texture and meat color

How does irradiation do so many different things?

• High doses damage or kills cells – Kills microorganisms or insects

• Lower doses alter chemical reactions and interfere with cell division– Delay fruit ripening– Prevent sprouting or parasite reproduction

Are irradiated foods safe to eat?

• Foods cannot become radioactive at energies used in irradiation

• Below 10 kGy there are no known toxicological, microbiological, or nutritional problems

Foods Approved for Irradiation in the United States

• Fresh fruits and vegetables

• Herbs and spices

• Pork

• Potatoes

• Poultry

Important Terminology

Ion: Atom that has been made electrically charged by the removal or one or more electron.

Gray: Unit of energy absorbed by a material. 1000 Gy = 1 kGy

Radura: Official symbol or logo indicating that food has been irradiated.