INTERCULTIVAR VARIATION IN THE QUANTITY OF MONOMERIC PROTEINS, SOLUBLE AND INSOLUBLE GLUTENIN, AND RESIDUE PROTEIN IN WHEAT-FLOUR AND RELATIONSHIPS TO BREADMAKING QUALITY

A new fractionation procedure based on differential solubility was app lied to wheat flour proteins to evaluate the relationship between prot ein fractions and functionality for breadmaking. Flour was initially e xtracted with 50% l-propanol. Monomeric proteins (mainly gliadins) and soluble glutenin contained in the 50% propanol soluble extract were f ractionated by selective precipitation of the glutenin by increasing t he concentration of I-propanol to 70%; monomeric proteins remain in th e supernatant. Insoluble glutenin in the 50% propanol insoluble residu e was extracted using 50% 1-propanol containing 1% dithiothreitol (DTT ) at 60 degrees C. Protein in the final residue was extracted using SD S with or without DTT. It comprised mainly Glu-ID high molecular weigh t glutenin subunits and nongluten polypeptides. For seven Canadian cul tivars of diverse breadmaking quality, there was relatively little var iation in the percentage of flour protein corresponding to monomeric p roteins (48-52%) and residue protein (14-18%). In contrast, interculti var variation in soluble and insoluble glutenin was substantial, with contents of 10-20% and 12-28% of flour protein, respectively. Soluble and insoluble glutenin were also highly correlated with physical dough properties, accounting for 83-95% of the variation of individual doug h rheological parameters (except dough extensibility), and approximate to 74% of the variation in loaf volume. In contrast, monomeric and re sidue protein fractions were poorly associated with breadmaking qualit y. However, among the four protein fractions, only residue protein was significantly correlated (r = -0.79) with dough extensibility. The fl our sample with the highest and lowest concentrations of insoluble and soluble glutenin, respectively, as well as marginally the lowest conc entrations of monomeric and residue proteins was Glenlea, a cultivar o f the Canada Western Extra Strong Red Spring wheat class which charact eristically possesses distinctly strong dough mixing properties.