2. 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
5. 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
6. • 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.
7. • 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.
8. 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
9. 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.
10. • Uv source in food industry is quartz
mercury vapor lamp. Ehich emit radiation
at 254 nm.
11.
12. Sources of Ionizing Radiation
• Cosmic Radiation • Power plants
(the sun) • Fertilizers
• Medical procedures • Smoke detectors
• Radon and other • Accelerators
terrestrial sources
• Nuclear weapons
fallout
13. 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
14. 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.
15. • 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.
16. 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
17. • Prevention of mold growth on walls in
production area.
• Treatment of air.
19. Irradiation Sterilization
• Very high dose used to kill all organisms
• Sterilization of > 50% disposable
medical instruments
• Food sterilization - NASA, military,
transplant patients
21. 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
22. 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
23. 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
24. 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
25. Foods Approved for Irradiation
in the United States
• Fresh fruits and vegetables
• Herbs and spices
• Pork
• Potatoes
• Poultry
26. 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.
