Proteins are complex molecules found in all living creatures. Although the main nutrients in cereals are carbohydrates, in wheat, rice, maize, oats, rye and other cereals, 7 to 12 percent are proteins, according to the Food and Agriculture Organization of the United Nations. Small units called amino acids form all types of proteins. Glutamine, proline and glycine are the principal amino acids forming cereal proteins, including albumins, globulins, glutelins and prolamins.
Albumins and Globulins
Albumins are proteins soluble in water, while globulins are only soluble in sodium chloride solutions, according to Long Ashton Research Station at the University of Bristol. The concentration and consequent solubility of these proteins vary from one cereal to the next. Albumins range from 4 percent in maize to 44 percent in rye, while globulins range from 3 percent in maize to 55 percent in oats, says the Food and Agriculture Organization of the United Nations.
Glutelins are insoluble in aqueous and saline solutions, or alcohol, but soluble in acids, says Long Ashton Research Station at University of Bristol. When associated with another protein called gliadin, it forms the gluten molecule. Among the cereals, rice presents more glutelins than any other protein, says the Journal of Agriculture and Food Chemistry. Rice glutelin is called oryzenin, while wheat main glutelin is glutenin.
Prolamins are complex mixtures of proteins found only in cereal grains. More than 20 years ago, the individual components of prolamins were divided in groups according to their solubility properties, including hordeins, secalins and gliadins, reports Long Ashton Research Station at University of Bristol. However, advances in molecular biology allowed more precise classification, observing amino acid sequence. The three major groups of prolamins today are called the sulphur-rich (S-rich), S-poor and high molecular weight (HMW) prolamins.
- Long Ashton Research Station at University of Bristol: Improving the Protein Content And Quality of Temperate Cereals: Wheat, Barley And Rye
- The Food and Agriculture Organization of the United Nations: Major Chemical Components of Cereal Grains
- Changes in peptide subunit composition of albumins, globulins, prolamins, and oryzenin in maturing rice grains