Some have measured only ascorbic acid, while others have measured total vitamin C, a mixture of ascorbic acid and dehydroascorbic acid. Both acids have vitamin C biological activity and are easily transformed from one to the other. If only ascorbic acid were measured, any apparent reduction in vitamin C level would be exaggerated. Just as vitamins vary in their sensitivity to heat, so do they vary in their sensitivity to radiation. This sensitivity depends upon the conditions under which food is irradiated.
Losses are generally less if oxygen is excluded and if the temperature during irradiation is low.
Under optimal conditions, vitamin losses in foods irradiated at doses up to 1 kilogray are considered to be insignificant. At higher doses the effect of irradiation will depend on the specific vitamin, temperature, dose, food, and packaging. Depending on the food, thiamine levels may be reduced further by storage and cooking if the food has been exposed to air during storage, but not necessarily if it has been packaged without oxygen. Safety and Nutritional Adequacy of Irradiated Food.