Gluten (from Latin gluten "glue") is a protein composite that appears in foods processed from wheat and related species, including barley and rye. It gives elasticity to dough, helping it to rise and to keep its shape, and often giving the final product a chewy texture.
Enough of the human population suffers from gluten sensitivity of one kind or another that many foods are now labeled to clarify whether they contain gluten.
Gluten is the composite of a prolamin and a glutelin, which exist, conjoined with starch, in the endosperm of various grass-related grains. Gliadin and glutenin (the prolamin and glutelin from wheat) comprise about 80% of the protein contained in wheat seed. Being insoluble in water, they can be purified by washing away the associated starch. Worldwide, gluten is a source of protein, both in foods prepared directly from sources containing it, and as an additive to foods otherwise low in protein.
The seeds of most flowering plants have endosperms with stored protein to nourish embryonic plants during germination. True gluten, with gliadin and glutenin, is limited to certain members of the grass family. The stored proteins of maize and rice are sometimes called glutens, but their proteins differ from wheat gluten by lacking gliadin.
Gluten is extracted from flour by washing out the starch: starch is water soluble while gluten is not, and gluten binds together strongly, while starch dissolved in cold water is mobile. If a saline solution is used instead of water, a purer protein is obtained, with certain harmless impurities going into solution with the starch. However, on an industrial scale, starch is the prime product, so cold water is the favored solvent. To effect the separation, a slurry of wheat flour is stirred vigorously by machinery until the starch dissolves and the gluten consolidates into a mass, which is collected by centrifugation, then carried, by complex machinery, through several stages combined into a continuous process. Approximately 65% of the water in the wet gluten is removed by means of a screw press, and the residue is sprayed through an atomizer nozzle into a drying chamber, where it remains at an elevated temperature only long enough to evaporate the water without denaturing the gluten. This yields a flour-like powder with a 7% moisture content, which is quickly air cooled and pneumatically transported to a receiving vessel. In the final step, the collected gluten is sifted and milled to make the product uniform.
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