Biochemical and Functional Properties of Wheat Gliadins: A Review

Gliadins account for 40-50% of the total storage proteins of wheat and are classified into four subcategories, alpha-, beta-, gamma-, and omega-gliadins. They have also been classified as omega 5-, omega 1, 2-, alpha/beta-, and gamma-gliadins on the basis of their primary structure and molecular weight. Cysteine residues of gliadins mainly form intramolecular disulfide bonds, although alpha-gliadins with odd numbers of cysteine residues have also been reported. Gliadins are generally regarded to possess globular protein structure, though recent studies report that the alpha/beta-gliadins have compact globular structures and gamma- and omega-gliadins have extended rod-like structures. Newer techniques such as Mass Spectrometry with the development of matrix-assisted laser desorption/ionization (MALDI) in combination with time-of-flight mass spectrometry (TOFMS) have been employed to determine the molecular weight of purified omega- gliadins and to carry out the direct analysis of bread and durum wheat gliadins. Few gliadin alleles and components, such as Gli-B1b, Gli-B2c and Gli-A2b in bread wheat cultivars, gamma-45 in pasta, gamma-gliadins in cookies, lower gliadin content for chapatti and alteration in Gli 2 loci in tortillas have been reported to improve the product quality, respectively. Further studies are needed in order to elucidate the precise role of gliadin subgroups in dough strength and product quality.