7. The Role of the Insolubility of Gluten
Cohesiveness is lost as the proteins become more soluble. Their native insolubility is due to a small and well-balanced amount of anionic and cationic amino acid side chains and of the end-groups of the subunits (Belitz et al., 1982). Changing the number of one sort of ion e.g. by derivatisation of amino groups to carboxylic groups (Dirndorfer et al., 1986) solubilizes gluten without changing the molecular weights, with the result that elasticity is lost completely.

When experiments in which the solubility of gluten is changed are used to deduce the importance of elasticity for wheat bread making, it must be kept in mind that in fact the composition of the dough is changed. In the case of reduced disulfide bonds, or when gluten fractions are made water-soluble, the nature of the gluten is changed completely, in other words there is no longer any gluten in the dough capable of generating cohesive structures. It is like cutting a rubber band in small pieces. The elastic behaviour vanishes because of a lack of cohesiveness of the pieces. There is still rubber, but no longer a rubber band.

A better way to prove the correlation between elasticity and baking quality is to compare flours from different wheat cultivars by the following rheological methods.

8. Methods for the Evaluation of Elasticity
8.1. Prerequisites for Physical Testing
Elasticity is only one component of the bulk property of gluten or dough, so methods must be used which show this property isolated from the others.

A second problem is that when gluten and dough are compared it is essential for both samples to have exactly the same dimensions. It is rather difficult to shape gluten. But this can be done by using parallel plate geometries with stress rheometers or the SMS/Kieffer gluten and dough extensibility method (Kieffer et al., 1998 and Mann et al., 2004) or highpressure capillary viscosimetry (Kieffer et al., 1982). The latter will not be considered as it is very time-consuming.

The third and most important question is what we want to see. Cereal chemists want to clarify the mechanism of elasticity on a molecular basis, and determinations in the field of linear viscoelasticity can be useful. If, on the other hand, the function of elasticity during dough preparation and for the resulting product is of interest, we first have to find the range of stress or deformation velocity; that means we have to imitate very closely what happens in dough. Because this is not so simple we have to vary test conditions until they are correlated e.g. to the baked volume. Using this approach, very useful empirical methods such as the Brabender methods have been developed.


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