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In Vitro Polymerization of Wheat Glutenin Subunits with Inorganic Oxidizing Agents. II. Stepwise Oxidation of Low Molecular Weight Glutenin Subunits and a Mixture of High and Low Molecular Weight Glutenin Subunits

¹Laboratory of Food Chemistry, Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92, B-3001, Heverlee, Belgium. ²Corresponding author. Phone: +32-16-321634. Fax: +32-16-321997. E-mail: wim.veraverbeke@agr.kuleuven.ac.be ³Grain Quality Research Laboratory, CSIRO Plant Industry. P.O. Box 7, North Ryde, NSW 1670, Australia.

High and low molecular weight glutenin subunits (HMW-GS and LMW-GS) were isolated from wheat flour. LMW-GS and a 1:2 (w/w) mixture of HMW-GS and LMW-GS were polymerized in vitro at pH 3.0 by stepwise oxidation with different oxidants (KBrO₃, KIO₃, H₂O₂). In analogy with the oxidation of HMW-GS, KBrO₃ produced smaller polymers for LMW-GS than KIO₃ or H₂O₂. While similar average sizes were found with flow-field flow fractionation for LMW-GS polymerized with KIO₃ and H₂O₂, multilayer SDS-PAGE and size exclusion HPLC indicated that size distributions were different. Significantly fewer monomers remained after polymerization of LMW-GS than with HMW-GS. The higher polymerization efficiency of LMW-GS was also obvious during polymerization of a mixture of HMW-GS and LMW-GS. Mixed polymerization of HMW-GS and LMW-GS had no observable effect on the polymer size. Multilayer SDS-PAGE of remaining monomers during polymerization revealed differences in polymerizing efficiency between structurally different glutenin subunits, with x-type HMW-GS and B-LMW-GS showing higher degrees of incorporation than y-type HMW-GS and C-LMW-GS, respectively.