Submitted to: International Archives of Allergy and Immunology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/24/2004
Publication Date: 1/15/2005
Citation: Kopper, R.A., Odum, J.N., Sen, M., Stanley, S.J., Burks, W.A. 2005. Peanut protein allergens: the effect of roasting on solubility and allergenicity. International Archives of Allergy and Immunology. 136(1):16-22. Interpretive Summary: One characteristic for food allergens includes the stability of proteins to pepsin digestion by in vitro methods. This does not take into account processing procedures for food marketing or for preparation as a food source. To get a better understanding of the in vitro digestion of peanut allergens, various methods were used to re-solubilize the insoluble peanut material following routine extraction. Roasting peanuts at different temperatures and for different time periods resulted in decreased solubility of the major peanut allergens. The effect of enzyme and different buffering treatments (acidic or basic) treatments demonstrated that a continued source of the major peanut allergens could still be presented to the mucosal immune system leading to food allergy.
Technical Abstract: Background: A contributing factor to food allergen stability is heat resistance. Peanut allergens in particular are resistant to heat, which results in their decreased solubility upon routine extraction and may have a profound influence on their continued presence in the digestive tract. Although there have been a number of studies characterizing soluble extracts of raw and roasted proteins, the relative solubility of the insoluble material following routine extraction for residual allergen characterization has not been investigated. The effects of various treatments on the re-solubilization and subsequent allergenicity of this insoluble peanut protein material are presented here. Methods: Various methods to re-solubilize the insoluble protein material were used including pH, proteases, and glycosidases. Protease digestion of non-extractable peanut proteins with pepsin, chymotrypsin and trypsin was performed in appropriate buffers as previously optimized for peanut proteins. Glycosidase activity in the presence of protease inhibitors was performed at pH 2. Digested samples were then subjected to SDS-PAGE/western blot analysis using serum IgE from peanut-sensitive individuals. Results: Progressive roasting of peanuts resulted in a significant decrease in protein solubility. The acidic proteins were re-solubilized moderately at high pH, with solubility decreasing as pH approached the pI of the protein. However, at pH 2 the solubility increased dramatically. More extensive re-solubilization was observed with amylase treatment, presumably due to cleavage of glycoside of glycoproteins. The protein released into solution had a high IgE binding capacity. While amylase was effective at resolubilizing this material, digestive tract proteases were not. Conclusion: The presence of these insolubilized peanut proteins provides a continuous source of major allergens to the gastrointestinal mucosal immune system.