Technology of Baked Goods - Sourdough Biotechnology - page 54

emulsifiers (e.g. mono- and di-glycerides), which increase the volume of the dough
and the gas retention and crumb softness of baked goods. It is interesting to note that
many of these improvers are naturally present in the wheat grain but they are removed
with the by-products (bran and germ) during milling.

3.3 Other Raw Materials

3.3.1 Water

Water plays a key role both during processing and for the shelf-life and sensory
properties of baked goods. On the basis of the definition used for studying poly-
mers, the adjective “plasticizing” is often used for water. This identifies a material
incorporated into a polymer to increase workability, flexibility and extensibility [ 25 ] .
The water is subjected to significant changes during processing, both in terms of
absolute quantity (total humidity) and availability (relative humidity).
The amount of water added to convert flour to dough has to ensure the hydration
of all hydrophilic components, especially proteins. The addition of this solvent
determines the radical change of the three-dimensional conformation of proteins. In
1973, following their observations with an optic microscope, Bernardin and Kasarda
described an “explosion” of flour particles when in contact with excess water, and
the rapid formation of protein strings [ 26 ] . This spontaneous rearrangement is
caused by the immediate exposure to water of the hydrophilic areas of proteins
which are rich in polar amino acids, while the more hydrophobic areas are hidden
inside. The interaction among different protein chains is ensured through the forma-
tion of disulfide bonds and through stabilization via hydrogen bonds and hydropho-
bic interactions. Gluten proteins undergo a kind of glass transition when they absorb
water, passing from the hard and glassy state to the soft and rubbery state [ 27 ] . Cuq
et al. [ 28 ] described the changes that occur during the bread making using state
diagrams and phase changes. The glass transition is the period of marked increase
in molecular mobility that involves amorphous polymers (e.g. proteins) or the amor-
phous areas of semi-crystalline polymers (e.g. starch). Amorphous polymers are in
the glass state at low temperatures and/or with low water content. An increase of
temperature or of the water content induces amorphous polymers to become soft
and viscoelastic. When the water content is higher than 15-20%, the glass transition
of proteins occurs below environmental temperature [ 28 ] . During mechanical mix-
ing, the relative mobility of the protein molecules and their high reactivity cause the
formation of intermolecular covalent links that are responsible for the formation of
the continuous and homogenous gluten network.
The level of water needed to obtain an optimal consistency of the dough is not
always easy to quantify. Overall, hydration less than 35% does not give an optimal
and homogenous hydration of gluten [ 29 ]. The absorption of water varies according to
the degree of refinement, granulometry, level of damaged starch, quantity and quality