Ionising radiation sterilisation

Ionising radiation sterilisation an absorbed radiation dose of at least 25 kGy. This method leads to breaks in the DNA of micro-organisms and, in presence of water, the formation of free radicals. 

The intensity of ionising radiation at the earth s surface is not high enough to significantly affect plastics, hence radiation exposure tests are only required in connection with applications in nuclear plant and possibly where radiation is used for sterilisation or to induce crosslinking. 

Different processes are applied to achieve this purpose, depending on the foodstuff involved. The technical possibilities available are pasteurisation and sterilisation processes, sterile filtration and the application of modified atmosphere packaging (MAP). The foodstuffs are chemically treated with preservatives. The application of ionising radiation is also permitted in some countries. 

Ionising radiation may be used during the manufacturing process for various purposes including the reduction of bioburden and the sterilisation of starting materials, packaging components or products and the treatment of blood products. 

STERILISATION (1) A process intended to produce sterile goods. (2) Reduction of the probability of the presence of viable micro-organisms to an acceptable extent. Sterilisation is effected by moist or dry heat by treatment with a gaseous sterilant such as ethylene oxide, by irradiation with ionising radiation or, where such processes are inapplicable to solutions, by filtration. 

Sterilisation can be affected by moist or dry heat, by ethylene oxide (or other suitable gaseous sterilising agent), by filtration with subsequent aseptic filling into sterile final containers, or by irradiation with ionising radiations (but not with ultraviolet radiation). Each method has its particular applications and limitations. Where possible and practicable, heat sterilisation is the method of choice. 

Sterilisation by means of ionising radiation of pharmaceutical preparations is not allowed in a number of countries. Many active substances and raw materials are decomposed by the doses required for sterilisation. Some polymers become brittle and glass may become discoloured. For these reasons there is only limited application for this sterilisation method for pharmaceutical preparations. Radiation sterilisation is however widely used in the medical device industry. 

Classical sterilisation techniques using an autoclave and saturated steam under pressure, hot water or dry heat are practical and reliable. Other reliable sterilisation methods include membrane filtration, ionising radiatirm sterilisation (gamma and electron-beam radiation) and gas sterilisation (ethylene oxide, formaldehyde). Sterilisation equipment (autoclaves, membrane filters, and other sterilisers) is often used in industrial manufacturing, in preparation in pharmacies, and in other healthcare establishments. Standard sterilisation processes are described in the Ph. Eur., in other current Pharmacopoeias, in ISO standards and National guidelines. 

For non-aqueous liquids, semisolids and dry powders 2 h sterilisation at 160 °C in dry heat is preferred. Where it is not possible to carry out terminal sterilisation by heat due to formulation instability, a decision should be taken to utilise an alternative method of terminal sterilisation, filtration and/or aseptic processing. It is recognised that new terminal sterilisation processes other than those described in the pharmacopoeia may be developed to provide sterility assurance levels equivalent to present official methods and such processes, when properly validated, may offer alternative approaches. If necessary, a different time-temperature combination may be applied to obtain an SAL of 10 . If too much degradation occurs in dry heat, ionising radiation or gas sterilisation can be applied. If these methods are not suitable either, sterilising membrane filtration and validated aseptic processing, sometimes robotised or with barrier system technology are considered as a last resort. 

Interest in the use of ionising radiation in the food industry was aroused in the mid-fifties with the availability of large isotope sources and the development of suitable electrical machines such as the linear accelerator. In particular, attention focused on the radioisotope cobalt 60 as a source of gamma rays. During the past 25 years it would be a reasonable estimate that some 50 million curies have been installed in plants situated in various parts of the world. However, the majority of these are employed for the sterilisation of disposable medical products, pharmaceuticals, cosmetic preparations, and laboratory animal diets. Only a few commercial fecilities have been constructed for the processing of human foods. 

---