Wheat gluten viscosity

Taylor N.W. and Cluskey, J.E. Wheat gluten and its glutenin component Viscosity, diffusion and sedimentation studies. Am/i. Biochem. Biophys. 97 399-405, 1962. 

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. 

Figure 11.6 Schematic representation of relationships between water activity, water content, Tg and viscosity for wheat gluten-based films. Calculated values were obtained using the (GAB) equation [176], Couchman and Karasz equation (CK) [171], and Williams Landel and Ferry equation (WLF) [153]. The critical water activity (aw) and Me are indicated when Tg is equal to the ambient temperature...

In order to optimise the process parameters (temperature, plasticiser content, residence time and so on), during the transformation of material proteins, the specific characteristics of each protein should be determined (thermal, mechanical and chemical sensitivities, and high viscosities of the rubbery phases above the Tg) for these new raw materials. However, the physico-chemical factors involved in these processes are unclear because very little is currently known about protein modifications that take place when processing at high temperature under low hydration conditions [182]. This has mainly been determined for wheat gluten-based materials [71,74,75]. 

Fig. 1.47. Viscosity curves during reduction of different wheat glutens. For sample designation see Fig. 1.44. (according to Lasztity, 1975)...

Rye Proteins. While rye is the only European cereal able to completely replace wheat in bread, rye protein is not as effective as wheat protein. One reason for this is that as much as 80% of the protein in a rye sour dough is soluble compared with 10% of soluble protein in a wheat dough. One factor that inhibits the formation of a gluten-like complex is the 4-7% of pentosans present, which bind water and raise the viscosity of the dough. The crumb structure is then formed from the pentosans in combination with the starch. 

Addition of gluten to 6.5-6.6% (w/w) dispersions of different starches at a 1% level ealeulated on dry stareh basis inereased the G of wheat and rye starches, lowered that of maize stareh but did not affeet the modulus of barley, triticale and potato starehes (Lindahl and Eliasson, 1986). G was also found to increase with increasing amounts of gluten (1-4%) added to the wheat starch. Studies on starches with different amylose/amylopectin ratios suggest that gelatinization of amylopectin and not amylose favors a synergistie interaetion with proteins leading to an increase in dispersion viscosity (Chedid and Kokini, 1992 Madeka and Kokini, 1992). 

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