What is gliadin?

Seed storage proteins (about 85% of endosperm proteins) are traditionally classified into monomeric (gliadins) and polymeric (glutenins) proteins, based on their solubility.

On the basis of electrophoretic mobility at low pH the wheat gliadins may be separated into the slowest group named the ω-gliadins and three faster groups, named the α, β and γ-gliadins.

The amino acids sequences of some gliadins are known. A very common N-terminal sequence found in α, β and γ-gliadins is Val-Arg-Val-Pro-Glu-Leu-Glu-Pro.

Due to the differences in cysteine content the gliadin components may be divided into S-rich (α, β and γ-gliadins) and S-poor (ω-gliadins) components.

All gliadin components have extremely high glutamic acid content. In some ω-gliadins the glutamic acid content is higher than 50%.

Although not major participants in the gluten polymer, the monomeric gliadins contribute to dough physical/chemical properties by extensive hydrogen bonding with the gluten polymer.

Gliadins are rather hydrophobic, hence their solubility in water or salt solution. More hydrophobic gliadins (the γ-gliadins) increase bread loaf volume, while gliadins from more hydrophilic end of the spectrum decrease loaf volume.
What is gliadin?

Gliadin protein in wheat flour

Gliadin is a heterogeneous group of prolamines. They are rather hydrophobic, hence their insolubility in water or salt solutions. They are single chain proteins and such disulfide bonds that occur are all intra-molecular. 

Gliadin is the major storage protein in wheat. Wheat flour has a total protein content of about 10% and approximately 10% of these proteins are made up of alcohol soluble gliadin proteins.

Gliadin is practically as abundant in the wheat kernel. The proportion of gliadin in wheat flour has much to do with its quality for bread making purpose. It is said that gliadin gives tenacity and elasticity to the gluten, while glutenin gives strength; but the two proteins must be present in proper protein of the gluten is to have the properties desired in bread-making.

In order to make a large light loaf of bread, the flour should have a fairly high gluten content and its gluten should contain a high proportion of gliadin.
Gliadin protein in wheat flour