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.