LPT 321: Meat Science (1+1)

RADIATION PRESERVATION OF MEAT

• Food and meat may be preserved by the application of radiation, either ionising or non-ionising, and such food is referred to as irradiated food.
• Ionising radiation is defined as radiation having energy sufficient to cause loss of electrons from atoms to produce ions.
• Non- ionising radiation is defined as radiation not having  sufficient energy to cause loss of electrons from atoms to produce ions.

Ionising radiations

• Ionising radiations include high speed electrons produced from a variety of electron generators such as cathode ray tubes, X-rays generated by electrons when they strike heavy metal, and electrons and gamma particles emitted from  radio–isotopes such as cobalt 60, cesium 137.
• Ionising radiation is capable of killing microorganism on meat without significantly raising the temperature, hence referred to as cold sterilisation.
• The amount of radiation energy absorbed by meat is expressed in rads (or) gray which is equal to 100 rads.
• A mega rad is a million rads or 10,000 Gray or 10 kGy.
• A dosage of about 4.5 megarads or 45 kGy is considered to be capable of sterilising products to a state where they can be stored without refrigerated storage.
• Radiation preservation may be classified as Radappertisation, Radurization and Radicidation in the decreasing order of dosage.
• Radappertisation,which brings about sterility in meat,  involves the application of radiation in the range 0f 20 -30 kGy.
• Hence it is also referred to as radiation sterilisation.
• It is oftern associated with development of unpleasant odours, flavors and off colours. 
• The odour that emanates has been likened to Wet Dog Hair odour.
• Beef is particularly liable to such changes while pork and poultry less so.
• Radurization is otherwise referred to as radiation pasteurisation, and this uses doses less than that required for sterilisation, typically in the range 1- 10 kGy, as this dosage is sufficient to kill many soilage organisms and thus can extend shelf life of meat under refrigeration significantly.
• Radicidation is a process in which doses less than 1kGy are employed to increase shelf life, prevent sprouting in vegetables and for rendering pork free of Trichinella spiralis.

Non-ionizing radiation

• Microwave and infrared rays have wavelength greater than visible lights are capable of generation of heat in the irradiated object and thus impart preservative effect, if any.
• Ultra violet rays  when absorbed by micro-organisms is lethal to them and thus germicidal.
  • It is used mainly in aging of meat.
  • Limitation of using ultra–violet rays are
    • Poor penetration,  so can be used only for sterilising  surfaces of carcasses and meat products.
    • Catalyzes many oxidative changes in the irradiated products. So, cause rancidity, discoloration and other type of oxidative deterioration and
    • Infra-red rays have been used to dry fruits and vegetables and for heat blanching in the same way as high frequency radiation.