Biomedical Engineering Reference
In-Depth Information
Table 8.1
Overall physical, chemical and biochemical changes in dough occurring by temperature
during the baking process (
http://www.classofoods.com/page2_3.htm
)
Temperature
increase (°C)
Changes in dough
30
Because of the rising temperature, gasses present in the dough
expand
Enzymatic production of sugars
Solubility of CO
2
decreases
45-50
Yeast dies
50-60
Intensive enzymatic activity
Starch starts to gelatinize
60-80
End of the gelatinization of starch
Enzymatic activity ceases because of the denaturation of the
enzymes
Crumb starts to form
Interaction between gluten and starch
100
Water starts to boil
Formation of water vapor
First signs of crust formation
110-120
Formation of pale yellow dextrins in the crust
130-140
Formation of brownish dextrins in the crust
140-150
Start of caramelization process
150-200
Formation of the “crustiness” of the bread and aromatic compounds
>200
Carbonization of the crust
Formation of a porous black mass
structure (Thorvaldsson and Skjöldebrand
1998
). The other changes are the formation
of carbon dioxide by leavening agents, crust formation, development of browning
by Maillard and caramelization reaction. Phase changes such as water evaporiza-
tion, and bubble expansion and coalescence are also occurred (Fan et al.
1999
;
Singh and Bhattacharya
2005
; Purlis
2010a
). Another major event during baking is
the loss of water from the product. The amounts loss during baking are directly
related to baking time and temperature (i.e. quantity of energy input). Water signifi -
cantly affects the quality of bakery products. However, certain level of water needs
to be kept during baking followed by cooling (Cauvain and Young
2000
).
Baking is a process of heat gain and moisture loss (Cauvain and Young
2000
).
Baking is considered as a simultaneous heat and mass transfer in a porous medium.
The temperature increase in a gas-free dough occurs at much slower rate than in
fermented dough. The conductive heat transfer is considered relatively minor
importance in dough baking, and evaporation-condensation is the major mechanism
of heat transport in baking. The theory of evaporation and condensation are as fol-
lows: (1) Water evaporates from the warmer region, absorbing latent heat of vapor-
ization, (2) Water vapor migrates through the gas phase, (3) The vapor condenses at
the colder side of the gas cell and releases its latent heat and, (4) Heat and water
transport by conduction and diffusion, respectively.
