Lesson 1: Celiac Disease - The Basics
1.1 What is gluten?
The term gluten is used to describe a mixture of storage proteins which are found in wheat, rye, barley and related grains. It is stored in the endosperm of the grain which is the source of nutrition for the growing plant embryo (=germ) (figure 1).
Figure 1: Anatomy of a grain
A grain consists of three main parts: the endosperm, the bran and the germ. The endosperm contains starch and many proteins including gluten.
Source: ENeA own
Grain proteins can be separated into two groups: water-soluble albumins and globulins and water-insoluble gluten proteins. As you can see in figure 2, gluten itself consists of two fractions: so-called prolamins and glutelins. It is the prolamin fraction which causes the problem in celiac disease by activating the immune system (Unit 1, lesson 3).
Depending on the source of grain, the protein structure of gluten slightly varies. Therefore, different names are given to the gluten proteins of different grains (see figure 2). You may sometimes come across these names in the internet or in books, especially gliadin. But in general, gluten is the umbrella term which is usually used.
Figure 2: Classification of cereal proteins from grains which are not tolerated in celiac disease
The system of naming (nomenclature) is however not always consistently used in the literature.
Source: ENeA own
The protein structures in wheat, barley and rye are very similar. Oats are less closely related to these grains and therefore its prolamin fraction, called avenin, is sufficiently different. This is the reason why almost all people with celiac disease tolerate oats very well. However, oats are only safe if they are labelled as gluten-free which guarantees that they were not contaminated with wheat or rye (learn more in Unit 3, lesson 1).
Other grains as rice and corn are even more distinct relatives. They do not contain gluten proteins that are harmful in celiac disease.
Why is gluten useful in food production?
Gluten in contact with water acts as a glue that holds food together. It helps dough to rise and to keep its shape, emulsifies water and fat and serves as carrier for flavors. Therefore it is not only found in many common foods that are based on gluten-containing grains, such as pizza, bread, pasta, cereals or beer, but is also widely used by the food industry for a variety of processed foods such as ready-to-eat meals, sauces, dressings or even light cheese, sausages and sweets.
In Unit 3 you will learn more about gluten-containing and gluten-free grains and foods.