In order to get prepared for the future practical use of irradiation for the purpose of controlling the microorganisms existing in proteinaceous food additives, we conducted studies on their water sorption isotherm and molecular weight distribution as their functional properties for gelation by irradiating three kind of them with electronic beams up to 25 kGy. The results of such studies were as follows: (1) In the case of a whey protein concentrate, only a few changes were observed in its water absorption volume and molecular weight distribution, and almost no change was observed in its gel strength; (2) In the case of a collagen, a decreasing tendency was observed in its water absorption volume, and a big change was observed in its molecular weight distribution, indicating that both polymerization and decomposition reaction were occurring simultaneously. In terms of its gel strength, however, no remarkable change was observed when irradiation was conducted below 20 kGy, while a weakening tendency was observed when irradiation was conducted at a high absorption dose such as at 20 kGy or above; (3) In the case of an egg white protein, slight increases were observed both in its water absorption volume and molecular weight distribution respectively, and changes in its molecular weight distribution indicated the occurrence of polymerization at a medium absorption dose and the occurrence of decomposition reaction at a high absorption dose; and (4) It is said that irradiation at 5 kGy is sufficient for the sterilization of proteinaceous food additives to kill the microorganisms existing therein, and in fact, an international absorption-dose guideline for the irradiation of foodstuffs also recommends irradiation at less than 10 kGy. It was confirmed by us that the function of gelation required of proteinaceous food additives as one of their main functional properties would not be affected by irradiation at such medium absorption-dose levels.
