Composition and stability of allergenic extracts made from gamma-irradiated rye grass (Lolium perenne) pollen.

Abstract

Phenol is commonly added to allergenic extracts as a bacteriostatic agent, but it is poisonous and also detrimental to proteins, which accelerates extract degradation. Sterilization by gamma-irradiation of the source material could be an alternative to the use of phenol. To analyse the potential effects of gamma-irradiation of pollen on the composition, potency, and stability of the resulting extract, and compare them with those of phenol. Ryegrass (Lolium perenne) pollen was sterilized by gamma-irradiation at a dose of 25 kGy. Extracts prepared from the irradiated pollen were then compared by electrophoresis techniques and RAST inhibition to extracts, without or with 0.5% phenol, from nonirradiated pollen. In addition, proteolytic activity was compared in extracts from irradiated and nonirradiated pollen. To evaluate the stability of extracts on storage, they were analysed after forced degradation for up to 7 days at 37 degrees C. When fresh extracts were analysed, there were no noticeable differences between the three types, as judged by immunoblotting and RAST inhibition experiments. However, on storage, extracts from irradiated pollen appeared to be superior to extracts from nonirradiated pollen, as some proteins were more stable in the former. This could be related to the lower proteolytic activity we have also observed in extracts from irradiated pollen. In contrast, extracts containing phenol degraded much faster, as proven by all our methods of investigation. Gamma-irradiation of pollen did not influence the IgE-binding capacity of the resulting extracts, but did yield extracts with somewhat improved stability, probably by reducing the proteolytic activity. It may be concluded that gamma-irradiation of the source material represents a good alternative to the use of phenol for the preparation of allergenic extracts.