Biomedical Engineering Reference
In-Depth Information
8.2
Baking Process and Structure Formation
The baking process is the most important step for the production of baked products.
This stage transforms the raw dough or batter (i.e. fl our, water and leavening agents)
to bread, cake or other bakery products with unique sensory features. This process is
achieved by the application of heat inside an oven. The most apparent changes
occurring during baking are volume expansion, crust formation, inactivation of yeast
and enzymatic, protein coagulation, gelatinization of starch, formation of a porous
structure and thermal expansion by carbon dioxide (i.e. produced by leavening
agents) and water vapor (Sablani et al.
1998
; Chang
2006
; Purlis
2010a
,
2011
).
During baking, suffi cient time should be given for the overall changes in the
attributes as discussed earlier. Rapid baking of dough results in a faster staling after
baking process (Le Bail et al.
2009
). Because of the above-mentioned changes, the
dough is transformed into crumb and then crust is subsequently formed due to water
evaporation, cross-linking reactions, and browning development (Purlis
2011
).
Cellular structure of soft baked products crumb is a vital quality indicator used in
commercial baking (Fig.
8.1
) (Scanlon and Zghal
2001
). The baking conditions are
very important in order to attain the desired quality. These conditions are generally
adjusted according to the time-temperature combination (Cauvain and Young
2000
).
The transformation of dough into bread during baking involves important structural
changes (Table
8.1
). For example, during baking at 220 °C, dough expansion and
coalescence of the bubbles occur during the fi rst 200-250 s, while a semi rigid elas-
tic solid or crumb take place up to 400 s. At longer time, signifi cant structural
changes do not occur in these dough as indicated by the values of the crumb features
and fractal dimensions obtained (Perez-Nieto et al.
2010
).
Leavened dough prepared by chemical or biological liveners. Many quality
aspects of baked products are the result of a series of irreversible physical and
chemical changes produced by simultaneous heat and mass transfer. The most sig-
nifi cant change occurs in starch and proteins. The denaturation of proteins releases
water while the gelatinization of starch absorbs water. These two phenomena occur
during the same temperature interval of 60-85 °C, and these contribute to the crumb
Fig. 8.1
Digital image of
bread crumb from a
white
sandwich bread
