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Quantitative Determination of High Molecular Weight Glutenin Subunits of Hard Red Spring Wheat by SDS-PAGE. II. Quantitative Effects of Individual Subunits on Breadmaking Quality Characteristics¹

¹Published with the approval of the director, Agricultural Experiment Station, North Dakota State University, Fargo. ²Graduate doctoral student and professor, respectively, North Dakota State University, Department of Cereal Science, Fargo, ND 58105, USA. ³Corresponding author, E-mail: kkhan@prairie.nodak.edu

High molecular weight (HMW) glutenin subunits were investigated in terms of “good” or “poor” subunits for determining the breadmaking quality of hard red spring wheat. Relationships between quantitative changes of individual HMW glutenin subunits and rheological properties of doughs and aggregation properties of native (nonreduced) glutenin proteins were investigated. Native glutenin proteins were separated by multistacking SDS-PAGE procedures. Seven genotypes with the same HMW glutenin subunits (2*, 7+9, 5+10) were used in correlation studies between solubilities of individual HMW glutenin subunits and physical properties of doughs, while three genotypes with diverse baking qualities were used to investigate solubility changes of HMW glutenin subunits during dough overmixing in the mixograph. Native glutenins in total flour proteins extracted with SDS buffer were separated based on their migrations at stacking gel origins of different acrylamide concentrations. After reduction of glutenin aggregates from the different origins with β-mercaptoethanol, compositions of HMW glutenin subunits were analyzed by densitometry. It was found that aggregates with the largest molecular weight at the 4% origin of stacking gels had much higher proportions of subunit 5 (18.8%) than those at the 12% origin (9.2%). For correlation studies, total flour proteins were fractionated into three fractions: salt-extractable (0.5M NaCl), SDS-soluble (2% SDS sodium phosphate buffer, pH 6.8), and insoluble residues. HMW glutenin subunits solubilized in SDS-soluble proteins were analyzed quantitatively by densitometry of SDS-polyacrylamide gels in relation to flour strength. The total amount of HMW glutenin subunits, x-type subunits, and proportions of subunits 5 and 2* in SDS-soluble proteins were found to have negative correlations with dough mixing strength (-0.87*, -0.76*, -0.94**, and -0.86*, respectively, with dough stability in the mixograph). Proportions of subunit 10 solubilized in SDS buffer had a positive correlation with flour strength (0.86*). In extended mixing studies, doughs with optimum mixing and doughs overmixed to 2.5 min after the peak in the mixograph were fractionated, and their protein compositions were compared using same procedures as for flours. During extended mixing, HMW glutenin subunits with the highest molecular weight (subunit 5) increased in solubility in SDS buffer, while subunit 10 (with lower molecular weight) decreased in solubility. These results indicated that functionalities and aggregation properties of individual HMW glutenin subunits may depend mainly on their molecular weights.