Original Paper

Mal d 2, the Thaumatin-Like Allergen from Apple, Is Highly Resistant to Gastrointestinal Digestion and Thermal Processing
Ursula Smole^a, Merima Bublin^a, Christian Radauer^a, Christof Ebner^b, Heimo Breiteneder<sup>a

a</sup>Department of Pathophysiology, Center for Physiology, Pathophysiology and Immunology, Medical University of Vienna, and
^bAllergy Clinic Reumannplatz, Vienna, Austria

Address of Corresponding Author

Int Arch Allergy Immunol 2008;147:289-298 (DOI: 10.1159/000144036)

  Key Words

• Allergenicity
• Circular dichroism
• Food allergen
• Protein stability

  Abstract

Background: The stability of food allergens to proteolysis and thermal denaturation contributes considerably to their allergenicity. Methods: Mal d 2, an allergenic thaumatin-like protein (TLP) from apple, was isolated and purified by anion exchange chromatography. Its IgE reactivity was tested by ELISA and immunoblotting using sera from apple allergic patients. The proteolytic stability of Mal d 2 was investigated using two in vitro digestion models. Effects of thermal treatment at different pH values on the secondary structure of the protein were recorded by circular dichroism. The level and IgE reactivity of Mal d 2 present in industrially prepared foods were assessed. Results: Purified Mal d 2 consisted of two isoforms. Both harbored carbohydrate moieties and bound serum IgE from apple allergic individuals. Mal d 2 showed remarkable stability to proteolysis and thermal treatments. The allergen remained intact after 2 h each of gastric and subsequent duodenal digestion retaining its full IgE-binding capacity. Mal d 2 was unfolded at neutral and acidic pH at 70°C. Refolding after cooling was only observed at acidic pH. Mal d 2 detected by an anti-TLP antibody in cloudy apple juice did not bind IgE of a serum pool of apple allergic patients. Conclusion: Our findings suggest that Mal d 2 maintains its structure in the gastrointestinal tract, a feature essential for sensitizing the mucosal immune system and provoking allergic reactions.

Copyright © 2008 S. Karger AG, Basel

  Author Contacts

Correspondence to: Prof. Heimo Breiteneder
Center for Physiology, Pathophysiology and Immunology, Department of Pathophysiology, Medical University of Vienna, Währinger Gürtel 18-20
AT-1090 Vienna (Austria), Tel. +43 1 40400 5102, Fax +43 1 40400 5130
E-Mail heimo.breiteneder@meduniwien.ac.at

  Article Information

Received: October 15, 2007
Accepted after revision: March 3, 2008
Published online: July 11, 2008
Number of Print Pages : 10
Number of Figures : 5, Number of Tables : 0, Number of References : 47