Peanut protein allergens: the effect of roasting on solubility and allergenicity

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.

Various methods to resolubilize the insoluble protein material were used, including pH, proteases and glycosidases. Protease digestion of nonextractable 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.

Progressive roasting of peanuts resulted in a significant decrease in protein solubility. The acidic proteins were resolubilized 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 resolubilzation 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.

The presence of these insolubilized peanut proteins provides a continuous source of major allergens to the gastrointestinal mucosal immune system.