BACKGROUND
Peanut allergy is extremely common, affecting approximately 1.5% of children in North America, Australia and the UK1. It is an important cause of anaphylaxis and utilization of hospital emergency room resources2. Most individuals with peanut allergy are not treated; rather, they strictly avoid peanut-containing foods and carry precautionary injected epinephrine in case of accidental ingestion.
In food allergies such as egg and milk, the rate of spontaneous resolution is considerably higher than for peanut. Indeed, children with egg or milk allergy can frequently introduce small amounts of well-cooked egg or milk into their diets safely as they grow3-6. Natural history studies of this practice have indicated that the patients are able to increase the cooked form of the allergen into their diets and ultimately a significant number evolve to complete tolerance7-9. Normal cooking processes denature or linearize egg or milk proteins, which may explain their decreased allergenicity, and frequent exposure for an extended period of time may act as a form of oral immunotherapy (OIT), albeit with more safety than conventional OIT10.
Peanut does not appear to denature under normal cooking conditions. Structural biology analyses have focused on the three-dimensional structure of the major peanut protein allergens and recent reports have thoroughly described their X-ray structures11-13. This class of proteins is rich in disulfide bridges, which explains their resistance to denaturation at high temperature14. In fact, glycation at high temperature is proposed to be a primary mechanism of enhancement of allergenic responses to peanut, as shown by quantification of IgE-binding15. Glycation primarily results from the Maillard reaction, an addition of amines on reducing sugars to provide Schiff bases that rearrange to form a wide range of products, of which the advanced glycation end-products (AGE) are believed to be of relevance to allergenicity16-19. Importantly, although the molecular composition of the peanut is now well known (i.e. proteins, amino acids, metal ion, sugar content)20, 21, the specific contribution of free sugars and amino acids to the enhancement of allergenicity of peanuts at high temperatures has yet to be defined22.
Previous studies suggest a decrease in IgE-binding in boiled and fried peanuts when compared with raw23, 24. It has been reported that low-molecular-weight proteins are transferred from the peanuts into the cooking water throughout boiling, particularly the 2S albumins Ara h 2, Ara h 6 and Ara h 7, potentially explaining a decrease in IgE-binding23. Moreover, it has also been found that autoclaving roasted peanuts produces a significant decrease of IgE-binding capacity of peanut allergens and in wheal size by skin prick test, as well as the unfolding of proteins and reduction in overall secondary structure25.
The objective of this study was to evaluate the effects of thermal processing, particularly roasting and autoclaving, on the resulting small molecule profiles, the major protein allergens, and thus, on peanut allergenicity.