Foodstuffs treatment by ionisation is a safe tool to produce both a shelf-life extension and/or a food-borne disease control through the pathogenic population reduction/elimination. The main goal is therefore to guarantee the best safe quality of the product to be marketed by means of a restriction of the spreading risk ("cross-contamination") for several diseases having an alimentary origin. About 50 countries provide clearances for the treatment of more than 50 different types of foodstuffs i.e.: spices, poultry, sea-food and vegetables. EU has to homogenise the situation producing a list of foodstuffs which can be processed. The costs are competitive with alternative treatment. In Tab. I doses used for food irradiation are reported. Current Italian legislation allows the treatment of:
a) potatoes, onions and garlic sprout inhibition dose;
b) Spices, herbs and condiments microbial load reduction dose.
The recent Law 94/2001, accepting the EU directives, allows radiation treatment also for all foodstuffs whose treatment is permitted in other EU countries. 10 kGy is the approved limit for irradiating food without prescription (1983 Codex Alimentarius Commission), but for sterilisation purposes it is important to reach limit up 50 kGy; thus our study was performed both at low and at higher dose levels.
Foodstuffs are submitted to irradiation treatment after they have been packaged. Thus the study of radiation effects on the package becomes crucial.
We performed our studies on several materials employed in food packaging.
The attention is pointed on the possible induced chemical-physical effects. The studied polymers were irradiated with a ?×-rays dose of 2-100 kGy from a 60Co ?×-cell (Fig. 1). Then we use the NMR spectroscopy method to study the effects. High resolution 1H and 13C NMR measurements were performed also at 600.13 MHz on a commercial spectrometer (Fig. 2). After plastic materials irradiation two main simultaneous effects occur: degradation and cross-linking, the net result depending on the comparative rates of the two reactions. According to the literature, Polystyrene (PS) undergoes cross-linking at very high doses of irradiation. Its mechanical properties are also slightly affected only at very high doses. Our data confirm that no significant effects can be observed under 100 kGy, both on commercial and purified polymer. Thus, due to its high resistance to radiation treatments, PS is a very suitable packaging material for irradiated foods.
Poly-butadiene (PB) very easily undergoes both cross-linking and degradation. In fact, 1H - NMR spectra show the presence of radiation-induced effects. The addition of stabilizers (BHT anti-oxidant) is recommended in PB-containing copolymers. In purified high impact polystyrene (HIPS), due to induced cross links, the stiffening of PS is clearly observable (Fig. 3). This phenomenon is not observable if the polymer is protected by an anti- oxidant.
Dr. Pietro Ragni
Chemical Methodolgies Institute
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