G.P. Branlard, UMR INRA-UBP, Amélioration et Santé des Plantes, 234 Avenue du Brezet, 63100 Clermont Ferrand, France; E.V. Metakovsky, Calle Montera, 42, Piso 6, Madrid 28013 Spain
Gliadin and Glutenin: The Unique Balance of Wheat Quality
Pages 115-139
DOI: https://doi.org/10.1094/9781891127519.006
ISBN: 978-1-891127-51-9
Abstract
Gluten is widely recognized as a water-insoluble network containing a complex physico-chemical system of flour components composed of polymeric glutenin and monomeric gliadins (Bietz and Wall 1972). The dough-mixing properties of flours are largely determined by gluten proteins. Glutenin is known to provide elasticity whereas gliadins mainly influence the extensibility and viscosity of the dough system (Finney 1943; Wall 1979; Mills et al 1990). Due to their recognized major impact on the bread-making process, these proteins have received a great deal of attention in the last two decades. Since the first genetic studies (Payne et al 1979; Burnouf and Bouriquet 1980), in which some high-molecular-weight subunits of glutenin (HMW-GS) were seen to be significantly correlated with the better technological values of bread wheat, many studies have been performed both on HMW-GS and low-molecular-weight glutenin subunits (LMW-GS). Gliadins are inherited at more complex Gli-1 and Gli-2 loci and they are much more polymorphic than the glutenin subunits, which are encoded at the Glu-1 and Glu-3 loci; consequently, the gliadins did not receive as much attention.
Although many points concerning the regulation of storage-protein synthesis and molecular events associated with glutenin polymerization remain unknown, the rheological properties of the gluten network are now predominantly attributed to glutenins. Gliadins, which represent approximately 50% of the gluten proteins, are often considered as merely acting as dilutents (MacRitchie 1992). From the standpoint of intercultivar differences, gliadins are considered to have an insignificant effect on dough rheology and their involvement in most of the wheat end uses, particularly in dough formation and swelling during baking, are still not well understood.
Pioneering studies, based on fractionation/reconstitution experiments, revealed the importance of gliadins in bread-making quality (Finney 1943, 1971; Hoseney et al 1969; MacRitchie 1987) and provided some evidence (not statistically based) of gliadin functionality in the end-use quality of wheat (Preston et al 1975; Kim et al 1988; MacRitchie et al 1990; van Lonkhuijsen et al 1992; Weegels et al 1994; Sapirstein and Fu 1996; Fido et al 1997; Hussain and Lukow 1997; Uthayakumaran et al 2001). The above-mentioned studies also resulted in some controversy, probably because extracting procedures may alter the functionality of the components and also because the genetic allelic differences were not taken into account. Higher gliadin contents were generally recognized to have a negative effect on dough strength and to be associated with higher viscosity and sometimes with lower loaf volume.
Changes in the polyacrylamide electrophoresis patterns and HPLC profiles were also observed between gliadin fractions during baking and cookie making (Schofield et al 1983; Menkovska et al 1988; Pomeranz et al 1989). However, the purpose of our review is not to discuss these controversial findings, but rather to develop the genetic approach, which is complementary to reconstitution experiments, with statistical analyses performed between gliadin alleles and technological tests. The nomenclature of the gliadin alleles, cited in our review, is adopted from Metakovsky (1991).
