Loaf volume and the intrinsic viscosity of glutenin

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Abstract
The intrinsic viscosities of glutens and glutenins from 36 English‐grown wheat samples (from 25 varieties including specimens from four countries in Europe) were highly correlated with their loaf volumes per gram of protein. At least 98% of the gluten protein appeared to be dissolved. If it is assumed that intrinsic viscosity of wheat proteins is correlated with molecular weight, as is found for linear macro‐molecules, these results mean that the molecular weight of the glutenin is an important contributor to the baking quality of wheat. The intrinsic viscosity of glutenin from a Canadian Western Red Spring wheat was higher than that of all the English wheats. It did not yield a good loaf volume because it was baked on a regime suitable for weaker wheats. Durum and barley fitted into the correlation pattern. A heat‐damaged wheat did not, and this and other evidence led to the inference that heat damage may be due to cross‐linking of glutenin molecules so that the molecular weight remains high but the ability to swell and form a continuous matrix is impaired. Genetic factors, rather than environmental, seem the more important in controlling the intrinsic viscosities of gluten and glutenin since no significant variations were detected when eight varieties were grown at more than one site or, in two cases only, in different years. Experimental proof that ηr could be adequately calculated as a ratio of efflux times was obtained.

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