Stability of antigen E in commercially prepared ragweed pollen extracts

Aqueous ragweed pollen extracts (20,000 PNU/ml or 78,000 PNU/ml) lose 50% of their Antigen E content within 5 months of storage at 4 degrees C. Glycerinated extracts and lyophilized ragweed pollen extracts retain their Antigen E content for over 15 months with little or no loss. The preservative phenol in aqueous extracts is destructive to Antigen E probably by protein denaturation. The stability of ragweed extracts as measured by Antigen E content is markedly enhanced with little loss after 15 month storage at 4 degrees C, when the extract is prepared as an alum precipitated suspension.