11. Viscoelastic Deformation
Elastic and viscous deformation can be monitored by observing and
drawing the filaments or bundles of filaments while these are immersed in the
water droplet. On extension beyond what is initially a purely elastic deformation
the relaxation of the filaments begins, at first without a visible thinning of
the strands. At greater elongation the thicker glutenin aggregates then slide
along each other. They seem to be lubricated by a gliadin film covering their
surface. This function of gliadin is probable, since the sliding movements are
strongly accelerated when pure isolated gliadin is added to dough. At further
elongation the filaments become thin and rupture. The ends of the filaments
contract to a globular shape, adopting the smallest possible surface because of
surface tension. Surface tension is also the reason why gluten forms in water
and dough, not gluten membranes enveloping gas bubbles. These microscopic
studies on gluten filaments demonstrate what happens in dough. They explain why
there is a measurable elasticity and why its amount is not related to volume
expansion.
Dough extends elastically in the first stage of proof, then on further
inflation it will begin to flow until the strands of the gluten network become
too thin and rupture. The moment of rupture and the maximum volume at a given
good shape of the dough piece will depend on the initial diameter of the
strands and the continuity of the structures. That means they will depend on
the cohesiveness of the gluten.
12. Elasticity: a Must for
Wheat Dough?
Our studies have shown that the intensity of elastic behaviour depends
on the method of determination and does not correlate with baked volume.
Elasticity may only be an overestimated phenomenon accompanying the other
physical parameters, which are viscosity and cohesiveness. The latter for
instance, being highly correlated to the degree of rupture of the gluten
network, or in other words to the maximum volume, is of immense importance.
Elasticity, which is closely connected to the cohesive structures,
seems to be nothing but an indicator of a persisting good continuous gluten
network. The fingerprint method for testing the degree of maturation of dough
is an example. But when we think of elasticity we always have in mind a round
balloon inflated by air. Is elasticity at least the reason for the rounded
bread shape? Or can we also get a good shape with non-elastic materials that
support dough stability? Such a material has yet to be found.
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