The chemistry of strawberry allergy

Not everyone can enjoy the fresh strawberries in summer. Some experience an allergic reaction with itching and swelling in mouth and throat. Biochemists at Lund University have identified a strawberry allergen among the thousands of proteins in a strawberry. Screening is now performed to find strawberries with no or little of the allergen protein. Sofar, a colourless, ’white’ strawberry variety has been found to be virtually free from the allergen.

The allergen was identified using blood sera from patients experiencing adverse reactions to strawberry. The protein then discovered turned out to be a not completely unknown one. “This protein resembles a previously known allergen in birch pollen,” says Cecilia Emanuelsson at the Dept of Biochemistry. A primary allergy against birch pollen can in turn evoke secondary allergic reactions against berries, fruit and some vegetables. That does not necessarily mean that all birch pollen allergic individuals react against strawberries. But some do; and some face the risk of developing such secondary adverse reactions. Birch-pollen related food allergy is a well-known phenomenon and especially common in Northern Europe, but the actual number of persons affected today is difficult to estimate.

There are some observations among breeders that allergic individuals can eat a white strawberry variety without problems. When the research group in Lund investigated such a white strawberry they found that it contained very little of the strawberry allergen. In Sweden breeders have worked for some time with breeding to improve the quality of white strawberries to become as tasty as the red ones. Some plant shops occasionally provide plants of white strawberry. “The allergen is in some way or other related to the red colour but it is not clear exactly how, we need to investigate more proteins,” says Rikard Alm.

He is specialized in bioinformatics, which helps to systematize and analyze the large datasets generated by today’s laboratory techniques. With so called proteomics it is now possible to find, investigate and compare the allergen with thousands of other proteins. “We are now investigating the biological variation of the strawberry allergen, between different strawberry varieties, and within one and the same variety depending on cultivation conditions,” says Rikard Alm.

The development of proteomics has accelerated due to partly classic techniques such as electrophoresis, where proteins are separated in an electric field and ending up in various places in a gel, and mass spectrometry. That large and complicated proteins can be analysed by mass spectrometry is new; and was awarded the Nobel prize in 2002. “The gel with the separated proteins is like a map, and it actually opens up new possibilities for plant breeding. By comparing e.g. strawberries with different properties and their maps with each other we may be able to discover which role different proteins play for e.g. frost resistance, colour, taste etc; and find biomarkers for different traits,” says Cecilia Emanuelsson.

The investigations on strawberry allergen was performed in collaboration with SIK (the Swedish Institute for Food and Biotechnology) in Gothenburg; with the Swegene centra for proteomics and bioinformatics at Lund University, and with specialists in protein mass spectrometry at the university in Odense. The project is financed by FORMAS, the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning.