| Summary: | The gluten proteins, gliadin and glutenin, are mainly responsible for the viscoelastic properties unique to wheat flour dough. This study was undertaken to evaluate the changes occurring to the gluten proteins during dough mixing and to examine how these proteins, related to breadmaking quality, participate in the mechanism of dough development and breakdown. Flours from four different cultivars, were selected for their wide range of nixing strength. Flour-water doughs and doughs containing potassium iodate or N-ethyl-maleimide were undermixed, mixed to peak development, and overmixed. A small scale fractionation procedure, coupled with a selective precipitation method, was used to obtain six protein fracti ns: salt-soluble (SS), ethanol-soluble (ES) gliadin and glutenin, acetic acid-soluble (AS) gliadin and glutenin, and acetic acid-insoluble (AI) glutenin. The presence of glutenin in the SS fraction and the formation of a foam layer during fractionation of doughs suggested that mixing altered the conformation of glutenin and/or induced gliadin-glutenin interaction to an extent sufficient to enhance the solubility and surface activity of some of the gluten proteins. Protein solubility distribution and electrophoretic results provided convincing evidence for the existence of genotype-specific gliadin-glutenin interaction. Results showed that all cultivars exhibited gliadin-glutenin interaction during mixing and the degree of interaction was inversely related to mixing strength. Analysis by reversed-phase high-performance liquid chromatography of changes in subunit composition during mixing of three glutenin fractions revealed some variation in subunits related to quality. Allelic differences were most pronounced for the 1Dx subunits (1Dx2 versus 1Dx5) and much less evident for 1Ax and 1B subunits. The 1Ax and 1Bx subunits appeared to be less affected by the mixing process. Using size-exclusion high-performance, liquid chromatography, the presence of glutenin comprised only of LMW-GS (LMW glutenin) was identified in the ES, AS and AI fractions of glutenin. LMW glutenin, like the gliadins, may be involved in interaction with the glutenin of the larger Mr. Results from this study provide additional support for glutenin breakdown and the sulphydryl-disulfide (-SH/SS-) interchange reaction as important mechanisms in dough mixing and offer convincing evidence for gliadin-glutenin interaction as an additional mechanism. This study concludes that glutenin breakdown occurs by both depolymerization and disaggregation and that the -SH/-SS- interchange reaction, like gliadin-glutenin interaction, exerts its functional importance at a higher structural level than the subunit level. (Abstract shortened by UMI.)
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