Influence of thermal processing on the allergenicity of peanut proteins

Peanuts are one of the most common and severe food allergens. Nevertheless, the occurrence of peanut allergy varies between countries and depends on both the exposure and the way peanuts are consumed. Processing is known to influence the allergenicity of peanut proteins. The aim of this study was to assess the effect of thermal processing on the IgE-binding capacity of whole peanut protein extracts and of the major peanut allergens Ara h 1 and Ara h 2. Whole proteins, Ara h 1, and Ara h 2 were extracted and purified from raw, roasted and boiled peanuts using selective precipitation and multiple chromatographic steps, and were then characterized by electrophoresis and mass spectrometry. The immunoreactivity of whole peanut extracts and purified proteins was analyzed by the enzyme allergosorbent test (EAST) and EAST inhibition using the sera of 37 peanut-allergic patients. The composition of the whole protein extracts was modified after heat processing, especially after boiling. The electrophoretic pattern showed protein bands of low molecular weight that were less marked in boiled than in raw and roasted peanuts. The same low-molecular-weight proteins were found in the cooking water of peanuts. Whole peanut protein extracts obtained after the different processes were all recognized by the IgE of the 37 patients. The IgE-binding capacity of the whole peanut protein extracts prepared from boiled peanuts was 2-fold lower than that of the extracts prepared from raw and roasted peanuts. No significant difference was observed between protein extracts from raw and roasted peanuts. It is noteworthy that the proteins present in the cooking water were also recognized by the IgE of peanut-allergic patients. IgE immunoreactivity of purified Ara h 1 and Ara h 2 prepared from roasted peanuts was higher than that of their counterparts prepared from raw and boiled peanuts. The IgE-binding capacity of purified Ara h 1 and Ara h 2 was altered by heat treatment and in particular was increased by roasting. However, no significant difference in IgE immunoreactivity was observed between whole protein extracts from raw and roasted peanuts. The decrease in allergenicity of boiled peanuts results mainly from a transfer of low-molecular-weight allergens into the water during cooking.