Radiation In Food Preservation

Food Preservation Storage

Lesson 13: Food irradiation

Radiation In Food Preservation

Ionizing radiation is the radiation with enough energy to remove electron(s) from atoms and molecules and to convert them to electrically-charged particles called ions. But, at dose levels approved for food irradiation, these radiations cannot penetrate nuclei and thus, food can never become radioactive. Other types of radiation energy i.e. infrared and microwaves are non-ionizing radiations with longer wavelengths. Infrared radiation is used in conventional cooking. Microwaves, due to their relatively longer wavelength, have lower energy levels but are strong enough to move molecules and generate heat through friction. Three types of ionizing radiations are approved to be used for food irradiation.

  • Electron beams generated from machine sources operate at a maximum energy of 10 million electron volts (MeV).
  • X-rays generated from machine sources operate at a maximum energy of 5 MeV.
  • Gamma rays are emitted from Co-60 or Ce-137 with respective energies of 1.33 and 0.67 MeV.

Electron beams
Electron beams are the streams of very fast moving electrons produced in electron accelerators. Electron beams have a selective application in food irradiation as they can penetrate only one and one half inches deep into the food commodity. Due to poor penetration, shipping cartons (pre-packed bulk food commodities) are not irradiated with electron beams. Electron beams can be switched on or off at will and require shielding as they are generated through machine sources.

Just like electron beams, X-rays are also generated through machine sources. X-rays are photons and have much better penetration and are able to penetrate through whole cartons of food products. X-rays also can be switched on or off at will and therefore, require shielding.

Gamma rays
Gamma rays are produced from radioisotopes either Cobalt-60 (Co-60) or Cesium-137 (Ce-137). Contrary to electron beams and X-rays, radioisotopes cannot be switched off or on at will and they keep on emitting gamma rays, therefore radioisotopes require shielding. Co-60 source is kept immersed under water when it is not in use and Ce-137 is shielded in lead. Due to their continuous operation, radioisotopes need to be replenished from time to time. Gamma rays are photons and have deep penetration ability.

Units of irradiation
Radiation dose is the quantity of radiation energy absorbed by the food as it passes through the radiation field during processing. The gray (Gy) is the unit used to measure absorbed dose of radiation and is equal to one joule of energy absorbed per kg of matter being irradiated.

1 Gy (Gray) = 100 rad (radiation absorbed dose)
1 Kilogray (kGy) = 1000 Gy

International health and safety authorities have endorsed the safety of irradiation for all foods up to a dose level of 10 kGy. Recent evaluation of an international expert study group appointed by Food and Agriculture Organization of the United Nations (FAO), the World Health Organization (WHO) and the International Atomic Energy Agency (IAEA) showed that food treated according to good manufacturing practices (GMPs) at any dose above 10 kGy is also safe for consumption, making irradiation parallel to heat treatment of food.
In India, the Ministry of Health and Family Welfare amended the Prevention of Food Adulteration Rules (1954) through a Gazette notification dated August 9, 1994, permitting irradiation of onion, potato and spices for internal marketing and consumption. In 1998 a number of other food items were permitted for radiation processing . Approval for additional items like fresh, frozen and dried sea foods and pulses have been given under FSSA regulations (2011).

Food items approved for radiation preservation under PFA Rules, 1955 and FSSA regulations, 2011

Name of food Purpose Dose (kGy)
Minimum Maximum
Onion Sprout inhibition 0.03 0.09
Potato 0.06 0.15
Ginger, garlic and shallots (Small onion) 0.03 0.15
Mango Disinfestation 0.25 0.75
Rice 0.25 1.00
Semolina (sooji, rawa), wheat atta and maida 0.25 1.0
Raisin, figs and dried dates 0.25 0.75
Meat and meat products including chicken Shelf-life extension and pathogen control 2.5 4
Spices Microbial decontamination 6 14
Fresh sea foods Shelf-life extension and pathogen control 1.0 3.0
Frozen sea foods 4.0 6.0
Dried sea foods Disinfestation 0.25 1.0

Source: http://www.barc.ernet.in/bmg/ftd/index.html and FSSA regulations (2011)

Last modified: Tuesday, 13 March 2012, 7:46 AM