GAMMA STERILIZATION IN PACKAGING INDUSTRY Dr. Hasan ALKAN
Gamma-Pak Sterilizasyon A.Ş., Istanbul

Gamma irradiation process has been applied in several industrial sectors for years. In addition to the packaging industry, gamma irradiation method is employed for the sterilization of injector infusion sets, operation gloves, operation threads and hundreds of other kinds of medical products, sterilization of medicine and medicine containers, eliminating the cosmetics and foodstuff from and their raw materials from the microorganisms or decreasing the total microorganism level.
Great improvements have been occurred in the sterilization of packaging materials for the last 15-20 years. Especially in the food and medical industries that require aseptic filling, disposal of the materials sterilized by gamma irradiation avoided the contamination stem from packaging and therefore product shelf lives are increased. Carton and plastic containers, bottles, metal and plastic taps, paper or plastic bags, layered cardboard, tin or aluminum boxes, plastic and aluminum tubes, injectors and several other packaging materials and several aseptic packaging products are sterilized by gamma irradiation. Irradiation of the packaging materials is a part of the sterilization process and it is mostly performed in Co-60 sourced gamma irradiation plants. Impact mechanism can be explained as killing the living organisms by destroying DNAs, which are very sensitive against radiation.
The aims of the irradiation process are both extending the storage life of the products on their physiologic and visual quality and avoid any pathogen infection. Actually the term sterilization is used to eliminate the microorganisms tend to reproduce. On the other hand today this absolute definition cannot be maintained by many sterilization methods. Even in the autoclave method (heat with humidity), which is very reliable, sterilization factor could not be more than 10-4 By means of gamma sterilization method very high sterilization levels have been employed. For aseptic procedures in general a factor between 10-3 and 10-4 is sufficient. For the sterilization of the packaging materials application 8- 10 kGy dose would suffice. The main reason for this the possibility of the material to include microorganism (microbe) is very high.
A great care shall be given for the selection of the food and medicine packaging materials sterilized by irradiation, because during irradiation free radicals are formed and they cause two significant reactions in macromolecules:
a) Cross-linking: separate combinations are formed among the molecules. As a result of this a positive change occurs on the material characteristics. Melting point increases and material become more rigid.
b) Chain breaking: the chain ends of the molecules are broken and as a result of this, material characteristics are deformed. In theory, these possible reactions might cause the formation of toxins. On the other hand researches have shown that there is no such a harmful effect in practice. In order to be in compliance with this modification the plastic manufacturers have created products that are not affected from gamma irradiation. In food packaging the most suitable polymers on durability and output aspects are polystyrene, PET, polyamid-6, polyethylene (low, middle and high density) and propylene. Briefly when the power and penetration of the gamma rays are taken into consideration, it is possible to decrease the microbiologic contamination even under very low doses and it seems as a suitable method to obtain required sterilization level. Gamma irradiation technology has been used in our country in medicine, health care and cosmetics and since 1999 in food sectors.

SOURCES:
1. Peter J.G Neijssen; Gamma sterilization of packaging nv-Export, 1992.
2. IAEA-TECDOC-539 Guidelines for Industrial Radiation Sterilization of Disposible Medical Products (Co-60 Gamma Irradiation) IAEA, Vienna 1990.
3. N.G.S. Gopal et.al. Guide for Radiation Sterilization of Pharmaceuticals and Decontamination of Raw Materials Radiat. Phys.chem. ,vol.32 p, 619,1988.
4. MDS Nordion, Suppliers of Gamma Compatible Materials Reference Guide 1996.
5. Report of a Joint FAO/IAEAI WHO Study Group High Dose Irradiation Wholesomeness of Food Irradiated with Doses Above 10 kGy World Health Organization Geneva 1999.