1. Introduction
Articles dealing with elasticity usually start by describing it as the
most important unique property of wheat. Elasticity is believed to account for
the high specific volume of bread and its high and rounded loaf shape when
baked without the support of a pan.
It is generally assumed that the simultaneous presence of elastic
proteins and special bread quality proves that elastic proteins are sufficient to
explain the good bread volume. However, what if it is just a coincidence?
Besides proteins and their elastic properties, numerous other flour
ingredients with functional properties are present in wheat which might be the
real source of the baking potential. So there is a need to analyse the function
of elasticity more closely.
2. Definition of Baking Quality
The definitions of bread quality vary from country to country and from
person to person. Sometimes a high specific volume or an elastic crumb are not
accepted as a sign of good quality. However, the volume measured at a defined
form ratio (height/width) is an international criterion for quality on the
wheat market.
The volume can be determined by standardized baking tests according to
the AACC or the ICC, or on a micro-scale with 7 to 10 g of flour (Kieffer et
al., 1993 and 1998). This is how the dependent variable for the analysis of the
correlation between bread quality and elasticity is defined.
3. Definition of Elasticity
Elasticity is closely related to vulcanized rubber. But the fully
cross-linked structure of rubber cannot be used to explain gluten elasticity.
Both are of high molecular weight, but gluten is a non-cross-linked material.
The molecules can be separated at least partially by dissociating agents like
sodium dodecylsulfate (SDS).
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| Fig. 82: Stretching of a piece of dough (left) and of gluten (right) in two dimensions, creating fissures |
"Elasticity" in bakery is a sensory perception that is felt
when the dough is rapidly stretched and released. Elasticity is good when the
dough contracts rapidly to approximately its original shape. In another test
the baker tries to stretch the dough into a thin membrane (Fig. 82). The
formation of membranes with no fissures is attributed to good gluten quality and therefore an indication of good elasticity. During kneading, dough
will wind up the hook when the kneading optimum approaches (Fig. 83). This
so-called Weissenberg effect is a sign of elasticity too. These observations
are mainly of a qualitative nature and lead us to expect a good product. A
scale for elastic behaviour can be derived from Hook’s law.
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| Fig. 83: Sensory testing of dough and the Weissenberg effect resulting from elasticity |
The deformation of an ideal elastic solid is totally recoverable. This
deformation is described by the equation:
An elastic solid will be the more extensible at a given force the
lower the modulus G is. So to determine G could objectify the sensory
tests.
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