Raw and Cooked Carrots Are Off the Table for Those With Allergies – But Why?

For those who are hypersensitive to raw carrots, there has been speculation into whether the heating process of the vegetable allows for consumption without triggering an allergic response. New research, conducted by scientists at the University of Bayreuth, shows that the heating process does not significantly alter the protein structures within carrots enough to enable them to be safely consumed by those with allergies.

Technology Networks recently had the pleasure of speaking with Prof. Birgitta Wöhrl from the University of Bayreuth, to learn more about the work herself and her colleagues are conducting, to analyze the protein structures and allergenic properties of the carrot, and why the allergen Dau c 1 is so resistant to heating.

Candice Tolton (CT): Could you tell us more about your recent study, the significance of your findings, and highlight some of the key analytical procedures used for this investigation?

Birgitta Wöhrl (BW): We showed that the carrot allergen Dau c 1 is a mixture of several structurally very similar proteins, called isoallergens. We analyzed the stability of natural Dau c 1 as well as different recombinant isoallergens and tested the structural stability and their allergenic potential upon heating and/or pH changes.

CT: When heated, the affected protein structures were reversibly changed, why is this significant to those who are sensitive to the carrot allergen Dau c 1?

BW: Some proteins that cause allergies lose their allergenic potential when cooked due to protein unfolding and loss of conformational epitopes. However, we show in our recent study that the Dau c 1 proteins from carrot unfold upon heating, but most of them refold when cooled down to room temperature, thus regaining their 3D structure and the conformational epitopes that are recognized by immunoglobulin E (IgE) antibodies, which trigger allergic reactions. We also found that even the unfolded proteins have allergenic potential, albeit somewhat weaker, indicating that linear epitopes must be present. Thus, cooking carrots does not abolish their allergenic activity.

Group leader Prof.  Birgitta Wöhrl analyzing results. The curve indicates the UV absorption of the separated proteins. Credit: Christian Wißler.

CT: Could the proteins be treated at a higher temperature to result in an irreversible structural change? Could this also be done if the pH were to be adjusted?

BW: We have not tested higher temperatures, however, this might considerably change the taste of carrot-containing food.

CT: Dau c 1 is comprised of several proteins, were some of these more immunogenic than others?

BW: Yes, we tested sera of different carrot allergy sufferers against the purified recombinant isoallergens. It turns out, that the immunogenic reactions can be quite different, and in individual sera usually not all isoallergens are recognized by IgE antibodies.

CT: Have Dau c 1 allergens been identified in other foods commonly known to trigger allergic reactions?

BW: Dau c 1 belongs to a family of proteins called pathogenesis related class 10 (PR-10) proteins which can be found in other fruits or vegetables – for example apple, hazelnut, celery, peach etc. Usually the homologous protein from birch pollen, called Bet v 1, initiates the allergy. The high structural similarity of PR-10 proteins from other plants causes the so-called cross reactivity of IgE antibodies, i.e. the antibodies originally directed against Bet v 1, also recognize PR-10 proteins from carrot, apple and other plants.

Prof. Dr Birgitta Wöhrl was speaking to Candice Tolton, Editorial Assistant for Technology Networks.