Studies in Depilation: III. Use of Gamma Radiation in the Sterilization of Sheepskins for Enzyme Depilation Studies

Sheepskin collagen was irradiated in the dry state (13 to 17% water content), and in the "green" (undried) state (60 to 67% water content), with doses from 1 to 20 megarads. Irradiation at any dose level causes some irreversible degradative changes to occur in the skin collagen, as manifested by a decrease in shrinkage temperature. These changes are more severe when the skins are irradiated in the dry than in the "green" state, and the damage cannot be fully compensated for by the introduction of new interchain cross-links in the tanning process. Irradiation changes the properties of the skins, and the water uptake, swelling (at neutral pH), and percentage loss of weight on soaking are all reduced. Doses of as high as 5 megarads do not confer long-term sterility on sheep-skins; furthermore, skin damage at this dose level is such as to preclude its use in practice as an alternative method of preservation to air drying. A dose of 3 megarads, however, will confer adequate short-term sterility over the course of laboratory enzyme depilation experiments, but wool loosening proceeds slowly even after a 5-megarad dose. Irradiation of a number of commercially available depilatory enzyme systems with a 5-megarad dose causes virtually no reduction in proteolytic activity, nor does it kill all the bacteria present in the preparations.