A two part study was designed to investigate radiation-induced structural and nutritional changes in food proteins. Model systems composed of 0.1-10% myoglobin, lactalbumin or BSA were used and the effects of propyl gallate, ascorbic acid, air or nitrogen, pH 5, 6 or 7 citrate or phosphate buffer, and addition of glucose and SDS were investigated. We found that 0.02-0.04% propyl gallate (PG), alone or in conjunction with other solutes, inhibited protein aggregation after irradiation to 0.5 and 1.0 megarad and subsequent -20 C storage for 3-6 months. PG alone at 0.04% yielded up to 90% retention of myoglobin after 0.5 megarad and up to 94% retention of lactalbumin after 1.0 megarad as compared to unirradiated controls. BSA appeared more radiation sensitive than other proteins, and use of 0.02% PG yielded retention of only 10% of the original protein after 1.0 megarad. Use of synergists such as glucose or SDS together with PG allowed up to a two-fold increase in protein retention, while use of 0.02% ascorbic acid led to lower retention compared to samples irradiated alone in control buffer. Irradiations at pH 5 and 6 yielded greater protein retention than at pH 7. Isoelectric focusing of myoglobin revealed acidic shifts in protein pI with new bands at pH 4.9-5.2 after irradiation at pH 6 with glucose and PG. A similar acidic shift was seen in focusing lactalbumin, with major new bands forming at pH 3.7-4.0 after irradiation in pH 6 phosphate with 0.04% PG. BSA showed a bipolar pattern of pI shifts after irradiation in pH 6 phosphate. Mice fed irradiated lactalbumin in factorial studies grew slightly faster and ate more than unirradiated controls, while those fed protein irradiated with 0.02% PG showed slightly decreased rates of gain and feed consumption. Amino acid analysis revealed a 35% decrease in lysine, as compared to control, in diets prepared with protein irradiated to 1.0 megarads in 0.05 M phosphate, pH 6 with 0.02% PG. The negative effects of PG on feeding and growth were reduced when protein was irradiated at 22.5% rather than 15% (w/v). Liver to body weight ratios among animals fed protein irradiated with PG were decreased by 18% in contrast to control animals fed identical, though unirradiated, diet. (Abstract shortened with permission of author.)

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A range of antioxidants (BHT, Irganox 1010, 1076, 1330 and Irgafos 168) were incorporated into polymers (polyethylene, polypropylene, polystyrene and polyvinyl chloride) and subjected to increasing doses of gamma-irradiation (1,5,10,20,25,35 and 50 kGy) from a cobalt-60 source. The amount of extractable antioxidant from the stabilised polymers was determined chromatographically and a gradual diminution in the total extractable levels of each antioxidant was observed as irradiation progressed, the extent depending on the nature of both the antioxidant and the polymer 2,6-Di-t-butyl-1,4-benzoquinone was shown to be an extractable degradation product, arising from the effects of gamma-irradiation on the phenolic antioxidants. The extractable degradation product arising from the phosphite antioxidant, Irgafos 168, was identified as tris(2,4-di-t-butylphenyl)phosphate. It was demonstrated using 14C-labelled Irganox 1076 that degradation products formed during gamma-irradiation are becoming covalently bound to the polymer, as a result of radical coupling processes. There is a pronounced increase in the extent of covalent binding from 0.4% before irradiation to a minimum of 12.4% after an exposure to 50 kGy. Evidence has also been presented of covalent binding of the degradation product of Irgafos 168 to the polypropylene matrix, via polymeric radicals formed during irradiation. Finally, the effects of gamma-irradiation on the extent of migration of antioxidants from polyolefins into food simulants was studied. It was found that irradiation leads to a decrease in the extent to which hindered phenolic antioxidants migrate from polyolefins into fatty media, consistent with the reduction in extractable antioxidant levels and the increase in the extent of antioxidant-polymer binding.

The effect of gamma irradiation on the emulsifying capacity of turkey light meat was studied in a model system. A change of emulsifying capacity due to the changes of functional capabilities of salt-soluble proteins were studied on the irradiated salt-soluble-protein extract by disc electrophoresis, viscometry, fluorescence spectroscopy and measurement of pH. The formed emulsions were taken for examination of the particle size under the microscope, measurement of the viscosity with a Haake Rotovisco Viscometer, and for the determination of the stability by a method of centrifugation and cooking. Irradiation of turkey meat at doses of 1 or 3 Mrad increased the emulsifying capacity of the tissue but doses of 2 or 4 Mrad decreased capacity relative to an unirradiated control. Irradiation had no effect on the extractability of salt-soluble proteins. The emulsifying capacity of irradiated salt-soluble-protein extract increased significantly ( p≤0.05 ) and viscosity decreased significantly ( p≤0.05 ) with increasing dose of irradiation from 0 to 2 Mrad. Doses of 3 or 4 Mrad failed to produce further significant change in either variable. Irradiation of the salt-soluble-protein extract also resulted in a decrease in particle size of the emulsion; an increase in viscosity of the emulsion; an increase of hydrophobic effect in the salt-soluble-protein molecule; an increase in the electrophoretic mobility of the two main protein fractions on polyacrylamide gel; an increase in pH; and an increase in the stability of emulsions judged on the basis of volume of oil in the supernatant after centrifugation and cooking. / Land and Food Systems, Faculty of / Graduate

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A histological investigation of the effects of ultraviolet (UV) radiation upon the skin of four species of teleost fish was conducted in an attempt to define the sequential pathogenesis of the UV induced lesion. The species used in the experiments, namely plaice Pleuronectes platessa L., turbot Scophthalmus znax.zmus (L.), rainbow trout, Sairno gairdneri Richardson and Atlantic salmon, Salrno salar L. represent species reared commercially and thus likely, in the artificial environment of a fish farm, to receive levels of solar radiation in excess of those encountered in nature. It was found that plaice were the most susceptible species to UV radiation whilst turbot were marginally less so. Rainbow trout and Atlantic salmon showed similar levels of susceptibility when compared with each other but, in addition, had significantly higher tolerance thresholds than either plaice or turbot. Whilst the use of artificial radiation sources allows for more accurate control over irradiance than would natural sunlight, the need to recognise the limitations of such sources has been emphasised. In addition the importance of incorporating filters to remove the shorter wavelengths which would not be encountered at the earth's surface has been demonstrated. The photoreactive capability/capability of fish skin to repair cell damage initiated by UV radiation has been shown by the use of variable light input in the visible spectrum. The use of scanning electron microscopy to examine the surface topography of the radiation lesion confirmed the observations made by light microscopy and demonstrated the vulnerability of the damaged skin surface to the invasion of opportunistic bacteria. The importance of recognising sunlight as an environmental factor in the initiation of dorsal skin damage is no longer in doubt; experimental evidence and clinical observations on high altitude fish farms confirm this. Consideration is also given to the implications of prolonged exposure to sunlight upon fish following transfer and handling. The possible role of sunlight in the aetiology of certain bacterial skin diseases in farmed and wild fish and in dorsal skin neoplasms in wild fish is discussed.

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