Gluten is a protein found in most grains, including wheat, rye, spelt, and barley. It is found in the endosperm (a type of tissue produced in seeds that are ground to make flour) and nourishes plant embryos during germination. Gluten is an enormous composite protein, the largest known, that consists of a strong, stretchy mesh of smaller proteins linked by molecular bonds. These smaller proteins are glutenin, which has a long, chainlike shape, and gliadins, which are shorter and round. The glutenin is what gives gluten its elasticity, whereas the gliadins give it strength. It is the combination of stretchiness and strength, together with its meshlike structure that can trap bubbles of gas, that makes gluten important in bread-making.
Structure of Gluten
Gluten is a resilient, rubbery substance that forms when glutenin and gliadin molecules in flour are mixed with water. The molecules bond together to form a mesh that can trap bubbles of gas - as occurs when dough is kneaded. Because the mesh is stretchy, the gas bubbles can expand without breaking it.