Structural Stability of Amandin, a Major Allergen from Almond (Prunus dulcis), and Its Acidic and Basic Polypeptides

Information relating to the resistance of food allergens to thermal and/or chemical denaturation is critical if a reduction in protein allergenicity is to be achieved through food-processing means. This study examined the changes in the secondary structure of an almond allergen, amandin, and its acidic and basic polypeptides as a result of thermal and chemical denaturation. Amandin (similar to 370 kDa) was purified by cryoprecipitation followed by gel filtration chromatography and subjected to thermal (13-96 degrees C) and chemical (urea and dithiothreitol) treatments. Changes in the secondary structure of the protein were followed using circular dichroism spectroscopy. The secondary structure of the hexameric amandin did not undergo remarkable changes at temperatures up to 90 degrees C, although protein aggregation was observed. In the presence of a reducing agent, irreversible denaturation occurred with the following experimental values: T-m = 72.53 degrees C (transition temperature), Delta H = 87.40 kcal/mol (unfolding enthalpy), and C-p = 2.48 kcal/(mol degrees C) (heat capacity). The concentration of urea needed to achieve 50% denaturation was 2.59 M, and the Gibbs free energy of chemical denaturation was calculated to be Delta G = 3.82 kcal/mol. The basic and acidic polypeptides of amandin had lower thermal stabilities than the multimeric protein.