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ABBREVIATIONS: GS, glutenin subunits; HMW-GS, high-molecular-weight glutenin subunits; LMW-GS, low-molecularweight glutenin subunits; MW, molecular weight; PAGE, polyacrylamide gel electrophoresis; RP-HPLC, reversed phase highperformance liquid chromatography; SDS, sodium dodecyl sulfate; SE-HPLC, size exclusion high-performance liquid chromatography.
ABSTRACT: The unique breadmaking properties of wheat are generally ascribed to the visco-elastic properties of its gluten proteins. While monomeric gluten proteins (gliadin) show viscous behavior, polymeric gluten proteins (glutenin) are elastic. The unique elasticity of glutenin results to a large extent from its polymeric nature. Glutenin is a highly heterogeneous mixture of polymers consisting of a number of different high- and low-molecular-weight glutenin subunits linked by disulfide bonds. Although glutenin obviously is the major polymeric protein in wheat, other polymeric proteins occur as well. Their importance in breadmaking may be underestimated. Nevertheless, variations in both quantity and quality of glutenin strongly determine variations in breadmaking performance. Structural features of different classes of glutenin subunits are described. Variations in glutenin quality may result from variations in its (1) structure, (2) size distribution, and (3) subunit composition. Some hypotheses on glutenin structure and current insights into the role of glutenin size distribution are evaluated. Finally, different ways in which variation in glutenin composition may directly or indirectly (by affecting glutenin structure and/or size distribution) influence glutenin quality are discussed.
KEY WORDS: wheat, protein, glutenin, breadmaking.
I. INTRODUCTION
Wheat is unique! Indeed, wheat flour is functional in a whole range of applications such as the production of leavened and unleavened breads, pasta, noodles and cookies. Its functionality significantly differs from that of flour from other cereals. Undoubtedly, many flour constituents play a role in wheat flour functionality. However, it is well established that the properties of its proteins are crucial. The range of applications for which wheat flour is used implies that wheat protein 'quality' is a complex concept that requires specification of the partitular application (e.g., a different functionality is required in breadmaking than in pastamaking).
In what follows, 'quality' is considered in relation to breadmaking. Wheat flours for breadmaking are derived from hexaploid Triticum aestivum wheats. Large differences in breadmaking quality of flours exist. Here we discuss the relationship between Triticum aestivum protein composition and breadmaking quality (overview in Figure 1). Furthermore, a more detailed overview of...