The glutenin macropolymer of wheat ̄our doughs: structure±function perspectives

Gluten is the main functional component of wheat, and is the main source of the viscoelastic properties in a dough. Dough properties are primarily governed by the structure of gluten, and interactions within the protein complex. While starch and water are the main components of doughs, the physical properties of a dough arise from interactions between gluten proteins, particularly the disul®de-bonded glutenin macropolymer. The primary structures of glutenin subunits are well characterized, but information on the speci®city and pattern on their interactions has been lacking, despite the fact that dough is one of the key food systems where the likely link between molecular protein structure and function is compelling. The structure of polymeric glutenin has been dicult to study since it comprises several dozen di€erent disul®de-bonded polypeptides in the molecular mass range of millions to hundreds of millions. Recently, a range of techniques has been used to help unravel structural information. These include biochemical methods, particularly chromatography and electrophoresis systems which are suitable for examining polydisperse high molecular weight protein complexes of limited solubility; small-scale rheological testing systems, in which the function of individual components (either isolated or from expressed genes) can be determined; and a range of microscopy-based techniques, including confocal light scanning microscopy, transmission electron microscopy, and scanning electron microscopy. Utilizing these techniques, an improved understanding of the relationship between polymeric glutenin structure and dough function has been obtained. It has been proposed that glutenin subunits provide a structural backbone to the glutenin macropolymer through the formation of disul®de bonds that are highly resistant to cleavage [1]. The inherent ability of glutenin subunits to form disul®de bonds is thought to be determined by the primary and secondary structure of the proteins, which determines whether cysteine residues are present and available to form disul®de bonds, the capacity of a subunit to fold in the manner that would be required to form the bond, and the elasticity of the subunit once in the polymer to provide visco-elastic properties to a dough [2]. In this review, we discuss the structure of the glutenin macropolymer of wheat ̄our and dough. # 2000 Elsevier Science Ltd. All rights reserved.