Wheat dough, viscoelastic properties

Although rye is used for bread-making, its dough viscoelastic properties are much inferior to those of wheat. Nevertheless, because its proteins do show properties more similar to wheat than do other nonwheat cereals, a detailed study of them seems to be justified to determine how they differ from wheat proteins. This could lead to better understanding of the requirements for dough viscoelasticity of nonwheat cereals. 

The peculiar viscoelastic properties of wheat dough are the result of the presence of a three-dimensional network of gluten proteins. The network is formed by thiol-disulfide exchange reactions among gluten proteins. Peptide disulfides can interfere in a thiol-disulfide exchange system by reacting with a protein (PR)-thiol to liberate a peptide (R)-thiol and form a mixed disulfide, as follows ... 

It is also important to remember that wheat gluten and dough are complex materials, consisting not only of protein and water, but also starch-, lipid-, water- and salt-soluble proteins and smaller carbohydrates, and so on. The properties of these materials and their interactions with the gluten proteins are poorly understood but can be expected to also influence the viscoelastic properties. The challenge therefore is to understand gluten structure at the molecular level and how this structure interacts... 

Faubion, J. M. and Hoseney, R. C. 1990. The viscoelastic properties of wheat flour doughs, in Dough Rheology and Baked Product Texture, eds. H. Faridi and J. M. Faubion, Van Nostrand Reinhold, New York, USA, pp. 29-66. 

Quinoa flour does not have good baking properties like wheat gluten proteins. The wheat proteins are able to form a viscoelastic network when flour is mixed with water to form dough, and these viscoelastic properties allow the use of wheat to produce bread and other processed foods (Shewry et al., 2002). Quinoa bread has been made by including 10% of wheat flour (Chauhan et al., 1992a,b). However, the enzyme... 

Dus, S. J., and Kokini, J. L. (1990). Prediction of the non-linear viscoelastic properties of a hard wheat flour dough using the Bird-Carreau constitutive model. J. Rheol. 34(7), 1069-1084. 

Which molecular processes are involved in the viscoelastic properties of wheat flour dough ... 

One of the questions posed in Chapter 1 was "Why does dough from cereals other than wheat not have viscoelastic properties " It is well established that the gluten proteins of wheat are responsible for the viscoelastic properties of wheat flom dough (see Chapter 6). The requirements for a protein (or any polymer) to exhibit viscoelasticity are discussed in Chapter 14. One of these is that the protein should be above its glass transition temperature (Tg). Zein, the prolamin protein of maize, is found to contribute viscoelastic properties to a zein-starch dough when the temperature is raised above its Tg at that water content (Bushuk and MacRitchie 1989 Lawton 1992). This shows that it is possible to obtain viscoelastic properties with nonwheat cereal proteins. 

The balance between viscosity and elasticity is close to optimum for wheat gluten protein at the water content used in dough-making. We have seen that the first requirement for a protein in dough to have viscoelastic properties is that its Tg be below the processing (usually ambient) temperature for the water content used. A second requirement for dough in an aerated product is that the molecular weight distribution (MWD) of the protein be optimal. 

Wheat starch is composed of two components itself amylose, a linear, amorphous polymer and amylopectin, a branched, semicrystaUine polymer (10). The protein is known as gluten, also composed of two polymers, gliadin, a low-molecular-weight, soluble polymer and glutenin, a high-molecular-weight, cross-linked, elastic polymer primarily responsible for the viscoelastic properties of bread doughs. 

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