Intercultivar Variation in the Quantity of Monomeric Proteins, Soluble and Insoluble Glutenin, and Residue Protein in Wheat Flour and Relationships to Breadmaking Quality

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Abstract
A new fractionation procedure based on differential solubility was applied to wheat flour proteins to evaluate the relationship between protein fractions and functionality for breadmaking. Flour was initially extracted with 50% 1‐propanol. Monomeric proteins (mainly gliadins) and soluble glutenin contained in the 50% propanol soluble extract were fractionated by selective precipitation of the glutenin by increasing the concentration of 1‐propanol to 70%; monomeric proteins remain in the supernatant. Insoluble glutenin in the 50% propanol insoluble residue was extracted using 50% 1‐propanol containing 1% dithiothreitol (DTT) at 60°C. Protein in the final residue was extracted using SDS with or without DTT. It comprised mainly Glu‐1D high molecular weight glutenin subunits and nongluten polypeptides. For seven Canadian cultivars of diverse breadmaking quality, there was relatively little variation in the percentage of flour protein corresponding to monomeric proteins (48–52%) and residue protein (14–18%). In contrast, intercultivar 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 dough rheological parameters (except dough extensibility), and ≈ 74% of the variation in loaf volume. In contrast, monomeric and residue protein fractions were poorly associated with breadmaking quality. However, among the four protein fractions, only residue protein was significantly correlated (r = ‐0.79) with dough extensibility. The flour sample with the highest and lowest concentrations of insoluble and soluble glutenin, respectively, as well as marginally the lowest concentrations of monomeric and residue proteins was Glenlea, a cultivar of the Canada Western Extra Strong Red Spring wheat class which characteristically possesses distinctly strong dough mixing properties.

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