Newsletter - August 2000

What Makes Some Plant Proteins Become Allergens

Most of the components in foods that cause allergic reactions are proteins but we do not know what makes some proteins more likely to become allergens. It is probable that the properties of certain proteins, together with the genetic factors that predispose certain individuals to becoming allergic, contribute to the allergenicity of food proteins.

A number of the properties common to plant food allergens contribute to both their resistance to cooking, and their resistance to break down during digestion. Both of these factors are important in making a protein an allergen. Many of the plant proteins that we eat are found in seeds and nuts, so much of the Project discussions have focused around the proteins found in seeds like Brazil nuts, peanuts and soya beans.

This is a picture of a lipid-transfer protein binding a lipid commonly found in food, palmitic acid. The protein is from barley and is not known to be an allergen, but it is very similar to the proteins in apples and peaches which can cause allergic reactions

One group of allergenic plant food proteins found in fruits are called non-specific lipid transfer proteins (LTPs). These proteins are very stable to cooking, and they resist digestion. If they bind lipid their resistance to cooking increases even more. This suggests that to understand allergy more fully, researchers need to start looking at food component interactions and not just individual protein allergens.

Plant Allergen Information

The availability of good quality information on food allergens is of interest to research scientists, the industry, regulators and consumer organisations. As part of the project workplan, the network has agreed upon a set of criteria relating to the types of information that would be useful to include.

This encompasses

• Biochemical characteristics (size, amino acid sequence, structural information, purification methods, effects of food processing)
• Clinical information (types and numbers of studies, symptomology, diagnosis)

Data on all the known plant allergens have been assembled into the catalogue, which is an electronic, searchable form. At present general information on the project and food allergies is available on this web-site together with links to other web-sites with useful information on food allergies. Once the data included in the allergen catalogue have been checked, we plan to publish it on the web-site as well.

Emerging Seed Allergies

Characterisation of sesame allergens

A nationally-funded study into the incidence of childhood sesame allergy is currently underway in Israel. Sesame containing foods, such as tahini and halva, are recommended as weaning foods in the Middle East, as they are rich in iron. However, there are concerns that this policy may result in an increase in sesame allergy in childhood. Symptoms seem to be more severe than for many other food allergens, and this has lead to the idea that sesame may be ëthe peanut of the Middle Eastí.

The study recruits allergic individuals from around 25,000 patients who visit child health clinics, where allergic conditions are recognised. To date 10 allergic children have been identified, three of whom had anaphylactic symptoms on consuming sesame-containing foods. The allergenic proteins in sesame are being characterised at IFR and preliminary results indicate that a low molecular protein is recognised which we are now trying to identify.

Ram Reifen, llan Dhal, Hebrew University of Jerusalem
Clare Mills, Institute of Food Research

This shows a fingerprint of the proteins found in sesame seeds produced using a method called SDS PAGE, together with those extracted with water (called albumins) and salt (called globulins). We think one of the allergens is a small protein at the bottom of the profile.

Allergenic Activity of Sunflower Albumins & LTP's

Sunflower seeds are being used both in toppings of foods such as breads, but also included as an ingredient in a variety of ëhealthyí lifestyle foods. There is also interest in exploiting the emulsifying properties of sunflower 2S albumins as novel food ingredients. In Greece, project partner Photini Papageorgiou has observed a number of sunflower-allergic patients and she is now characterising their allergies with Arthur Tatham (Institute of Arable Crops Research, UK). Using highly purified sunflower proteins they have found that one of the most active proteins was the LTP fraction. Further investigations are now in progress to confirm the preliminary results of this study.

Photini Papageorgiou, University of Athens
Arthur Tatham, IACR-Long Ashton

HPLC profile: This shows the fingerprint of a dilute salt extract of sunflower proteins obtained by chromatography using reverse-phase HPLC. The arrow points to the peak corresponding to the protein we think is the major allergen - an LTP.

New Projects

A project is currently being negotiated with the Commission to investigate food allergies across Europe. It is called ëPlant Food Allergies: Field to Table Strategies for Reducing their Incidence in Europeí and is co-ordinated by one of the Protall partners, Karin Hoffman-Sommergruber, and involves two other Protall members, Clare Mills (IFR) and Ronald van Ree (CLB, Amsterdam). The project seeks to develop strategies for reducing the allergenicity of plant-based foods by using modern genetic methods to identify plant varieties naturally low in allergens, and studying the effects of growing conditions on allergen levels. This will be coupled with optimising post-harvest handling and subsequent food processing for low-allergenicity foods, thus providing an integrated approach to low-allergen food production.

It focuses on apples as an example, as around 1 million Europeans suffer from allergy to such fruits. As well as characterising mild and severe fruit allergies from the Netherlands, Spain and Austria, the project will investigate the allergic consumersí attitude, together with those of the general population, towards new methods for producing low-allergen foods.

New Members

The partnership of Protall has changed over the last year, and several new members have joined including David Reading who heads an action group for severely allergic individuals called the Anaphylaxis Campaign. More information on the campaign and contact details can be found at www.anaphylaxis.org.uk He brings an extensive experience of communicating the problems of allergy sufferers, and represents the allergic consumers in the project. 

Another new member is Ronald van Ree who heads the sub-laboratory for Allergen Characterization & Standardization at CLB at the University of Amsterdam in the Netherlands. He has extensive interests in the identification and immunochemical characterization of inhalant and food allergens, particularly the role of LTPs in food allergy.

View list of participants