Biomedical Engineering Reference
In-Depth Information
0.1 N/10 g of dough. The values of TTA range from 30 to 150 ml NaOH 0.1 N/10 g
for liquid to 40-220 NaOH 0.1 N/10 g for dried sourdoughs. Nevertheless, the
optimal value of TTA for the sourdough depends on the type of bread. Overall,
sourdough with high TTA are preferred for bread making with rye flour (
48
) .
Fermentation Quotient (FQ)
. FQ indicates the molar ratio between lactic and acetic
acids during sourdough fermentation. After the determination of the concentration
of lactic and acetic acids by enzymatic or chromatographic methods, the FQ is cal-
culated as follows: FQ = (g of lactic acid in 100 g of dough/molecular weight of
lactic acid): (g of acetic acid in 100 g of dough/molecular weight of acetic acid).
This parameter is strictly related to the type of lactic acid bacteria dominating
the fermentation and markedly varies depending on the balance between homo-
and hetero-fermentative lactobacilli. In turn, this balance depends on exogenous and
endogenous factors which prevail during fermentation (e.g. fermentable sugar and
oxygen concentration, DY, time and temperature, etc.).
4.7
The Use of Stabilized Sourdoughs Versus
Active Sourdoughs
On the basis of the research progress in the field of bread-making biotechnology,
novel types of sourdough have recently been developed with the main aim of
improving the flavour of leavened baked products without using traditional protocols
of manufacture based on active sourdough. Currently, various commercial
preparations of stabilized sourdough are available on the market. They are used for
making traditional breads and are based on a mix of tailor-made aroma compounds.
Different types of stabilized sourdough are obtained starting from an accurate
selection and mix of raw materials (e.g. flour from
T. aestivum
or
T. durum
wheat, rye
or other cereals) and microbial strains. Dried sourdough is a type of stabilized prod-
uct useful for this purpose. Different drying protocols can be applied, for example
freeze-drying, spray granulation, fluidized bed drying, spray drying and drum dry-
ing, among which the latter two can be cited here as the most common for type III
sourdough production (
12,
48
). In both cases, the higher the DY of the starting type
II sourdough the higher the resulting TTA value of the derived type III sourdough,
which also increases due to water evaporation. In the spray-drying process, the liquid
sourdough is dried by using a warm air flux that removes water until the humidity
becomes less than 10%. In the drum-drying system, the vapour of the warmed drums
removes water from the thin-layered liquid sourdough during contact. On the basis
of various combinations of time and temperature and on the extent of the Maillard
reaction, different type III sourdoughs are obtained, which show different degrees of
caramelization or toasting and, as a consequence different flavouring activities. Since
many volatile compounds (especially acetic acid) are missing due to the evaporation,
even if to a different extent depending on the drying technique, pasteurization, cool-
ing or salting can be applied to obtain a stabilized liquid or pasty sourdough (
12,
48
) .
With the exception of cooling, all the other stabilization systems lead to microbiota
inactivation and stop gas and/or acid production (
48
), giving a sourdough which can
