Radiation applications have been enlarged and improved in the last twenty-

STUDIES ON SPECTROSCOPIC PROPERTIES OF THE RADICALS PRODUCED IN SOME FOODSTUFFS AFTER IRRADIATION AND DETERMINATION OF DOSIMETRIC POTENTIALS OF THESE FOODSTUFFS (2000)

(PhD. Thesis, Hacettepe University)

Radiation applications have been enlarged and improved in the last twenty-twenty five years. Radiation is used in different area from radiosterilization which requires high doses to food irradiation aiming to avoid the germination, to delay ripening and to kill the bacteria and insects likely existing in foods for prolonging their shelf-lives. However, treatment of foods by radiation has not been widely accepted in the world. Consumers are suspicious about irradiated foods and they are observed to refrain themselves from consuming these foods. The investigations carried out under the leaderships of World Health Organization (WHO), Food and Agricultural Organization (FAO) and International Atomic Energy Agency (IAEA) have shown that the foods irradiated up to a dose of 10 kGy did not lose their food qualities and that they did not present any risk for consumer. Basing on this conclusion, many countries in the world have accepted the irradiation of some foods to avoid loss. But the difficulty encountered at this point was to develop a dose measurement technique applicable to a wide range of foodstuffs enabling a good check about whether the upper permitted dose limits have been followed or not in the food irradiation plants. Studies have shown that the characterizations of the radiolitic intermediates produced after irradiation in the foods containing solid sections could be made best reliable, sensitive and encouraging detection techniques such as Electron Spin Resonance (ESR) and Thermoluminescence Dosimetry (TLD). In the cases where the stable radicals are produced after irradiation, ESR has been shown to be well suited for the diagnosis of the irradiated foods and for the effective dose determination purposes.

In the present PhD work, the spectroscopic features and the production and the decay kinetics of the radicals produced upon irradiation in some cereals (such as wheat and rice), pulses (such as lentil and white bean) and spices (such as red pepper) were studied using ESR technique at low and high temperatures. After irradiation of these foodstuffs at room temperature at different dose levels, the dose-response curves were constructed. An evaluation was made whether these foodstuffs could be used or not for industrial, health and nuclear accident dose measurement purposes basing on the data obtained from these curves.

The foodstuffs were irradiated both at the Chemistry Department of Hacettepe University and at the Turkish Atomic Energy Agency Sarayköy Irradiation Plants using ⁶⁰Co g-ray sources, at different dose levels. The samples were then transported quickly from the irradiation sites to the Magnetic Resonance Research Laboratory of Hacettepe University Physics Engineering Department where the ESR spectra were recorded immediately. The changes with the irradiation doses of the signals produced after irradiation were investigated for each food species studied in the present work using recorded spectra. The temperature dependent variations in the radical signals were studied in the temperature range of 130-400 K for all samples to determine in which temperature region, these samples could be used for dosimetric purposes. The radical stabilities were also investigated using the spectra of the samples recorded at room temperature at regular time intervals. The decay activation energy values of the radicals produced in the wheat, lentil and red pepper were also determined using the decay data of the related radicals at different temperatures.

The radical species were also proposed for the foodstuffs studied in the present work. The values of the spectroscopic parameters relative to each proposed radical species were determined through the detailed simulation calculations.