Wheat and gluten: Technological and health aspects

Peer-reviewed │ Manuscript received: December 09, 2015 │ Revision accepted: May 13, 2016

Cereals and cereal proteins

Cereals are among the most important raw materials in the world and are grown on about 60 % of agricultural land. In 2014, more than 2.5 billion tons of cereals were harvested, the main ones being maize (986 million tons), wheat (727 million tons) and rice (714 million tons) [1]. Cereal products are among the most important staple foods, particularly bread. With a mean content of only 10 %, proteins are not the main ingredient of bread. Nevertheless, cereal proteins provide about 30 % of human protein requirements, due to the high levels of consumption.

According to the extraction scheme developed by Osborne [2], cereal proteins can be classified into the fractions of albumins, globulins, prolamins and glutelins, depending on their solubility in water, dilute salt solutions, 70 % ethanol and dilute acetic acid or alkali. The albumins and globulins are metabolic proteins, with functions during grain development. Prolamins and glutelins are storage proteins, which make up about 70–80 % of grain protein and which occur in the starchy endo- sperm of different cereal grains. Prolamins mostly occur as monomers, whereas most of the glutelins are polymers linked through intermolecular disulphide bonds which can be converted to monomeric subunits by reduction. Like the prolamins, glutelin subunits are soluble in aqueous alcohols. Common names for these storage proteins are gliadins (prolamins) and glutenins (glutelins) from wheat, hordeins from barley, secalins from rye and avenins (only prolamins) from oats. Both the prolamin and glutelin fractions contain numerous protein components; these can be classified as high molecular weight (HMW), medium molecular weight (MMW) and low molecular weight (LMW) groups on the basis of their homologous amino acid sequences and similar molecular weights. Within the groups, close- ly related proteins are subclassified into individual types (• Table 1) [3].

Summary

Among the gluten-containing cereals only wheat contains gluten that converts flour into a cohesive, viscoelastic dough after mixing with water. Due to its high gas holding capacity, wheat dough is the basis for bread with high volume and typical crumb structure as well as for a variety of different baked goods. On the other hand, in some individuals, the consumption of wheat and gluten-containing cereals, such as rye and barley, triggers hypersensitivity reactions; these include wheat allergy, coeliac disease or non-coeliac gluten sensitivity (NCGS). The only effective therapy for these individuals is to avoid exposure by strictly following a gluten-free diet. The great majority of the population (90–95%) do not exhibit hypersensitivities and have no scientific reason to avoid products from gluten-containing cereals.

Keywords: gluten, baking properties, non-coeliac gluten sensitivity, wheat allergy, coeliac disease

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