5 key food allergens have been identified in barley, Hor v 12, Hor v 15, 16, 17 and Hor v 20.

Additionally Hor v 5 is an airway allergen, so is important for those sensitised to barley pollen.

Hor v 12 is a profilin protein, these are panallergens which have been found to cause allergies in many foods.

Hor v 20 is a gamma hordein and is the allergen most commonly linked to cross reactivity with other grains. Hordeins belong to the prolamin group of proteins which also includes gliadin, secalin, zein, kafirin and avenin. Reactions to this group of proteins is strongly linked to coeliac disease.

The other allergens are alpha and beta amylases - these are proteins also found in wheat. Amylases in plants are used to break down stored starches to aid in plant growth.

Malted barley is barley which is left to germinate and then the process is stopped quickly by heating. This process turns the starches in the plant to sugars which can then be used to make vinegars, whiskeys and beer. Malting barley does not neccessarily breakdown any allergenic proteins, in fact the amylase proteins in barley are increased by the process.

As barley contains a gamma hordein it is commonly linked to exercise induced anaphylaxis, more specifically to wheat dependent exercise induced anaphylaxis. This is because the gamma hordein is similar in structure to omega-5 gliadin's found in wheat.

Coeliac disease (celiac disease is the American spelling) is not an allergic condition, but is triggered by gluten found in wheat and there are similarly shaped proteins in barley to which sensitive individuals may react.

Allergy to wheat is sometimes linked to Celery-Mugwort-Spice Syndrome as the sensitising allergen is a profilin protein called Art v 4, these proteins are also sometimes also called Bet v 2 proteins.

There is a link between wheat and Latex Food Syndrome. The plant involved in latex allergy Hevea brasiliensis, the rubber tree plant, has an allergen called Hev b 8 which is a profilin protein. Those very sensitised to latex may have a contact allergic reaction from other foods or plants containing profilin proteins, there is less evidence of this than sensitisation to other latex linked proteins like hevein and chitinases.

Barley is in the Poales order of foods, so there may be some cross reactivity with other foods in the group such as wheat, rye and maize.

Profilin proteins are also found in pineapple, celery, peanut, chilli, watermelon, orange, hazelnut, carrot, strawberry, soya, barley, walnut, lychee, lupin, apple, banana, dates, cherry, kiwi, peach, pear, mustard, tomato, aubergine and wheat.

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