Biomedical Engineering Reference
In-Depth Information
emerge [
40
]. Anyway, the direct environment is another important source of
(accidental) contamination of the flour by LAB and yeasts. Consequently, hygienic
conditions in the sourdough and bakery environments will play a role as well.
Finally, microorganisms occurring on cereals and subsequently in sourdoughs may
be of intestinal origin, due to fertilization practices on the grain fields, mouse feces
or insects in the flour mills, or fecal contamination of the sourdough production
environment [
70,
175-
178
]. It may explain the opportunistic presence of
Lactobacillus acidophilus
,
Lactobacillus johnsonii
,
Lb. reuteri
, and
Lb. rossiae
,
which are common gastrointestinal inhabitants.
5.2.3
In fl uence of Technology
Besides the cereals and other dough ingredients, which are mainly responsible as the
source of metabolic activity in the form of flour enzymes and endogenous microor-
ganisms, specific technological process parameters determine the species diversity,
number, and metabolic activity of the microorganisms (whether or not added) present
in the stable, ripe sourdough. These process parameters include chemical composi-
tion and coarseness of the flour, leavening and storage temperature, fermentation
time, pH, redox potential, dough yield, refreshment time and number of propagation
steps, and interactions between the microorganisms [
57,
102,
164,
165,
179
] .
Different types of sourdough exist, on the basis of the processing conditions and/
or technology used for production, with a specific microbiota occurring in each type
[
57,
180
]. Type I or traditional sourdoughs are manufactured by continuous, (daily)
backslopping, at ambient temperature (<30 °C), to keep the microorganisms in an
active state. Therefore, mother doughs are used as an inoculum for subsequent
doughs by addition of the desired amount of dough to a fresh flour-water batch
according to defined cycles of preparation. These small-scale sourdough produc-
tions are used in traditional (home-made) sourdough bread making. Natural sour-
doughs frequently harbor
Lb. sanfranciscensis
and
C. humilis/K. exigua
as prevalent
LAB and yeast species, respectively. Type II or industrial sourdoughs are produced
through one-step propagation processes of long duration (typically 2-5 days) at a
fermentation temperature above 30 °C and with high water content. These large-
scale sourdough productions result in semifluid preparations, which are used as
dough acidifiers or flavor ingredients.
Lb. amylovorus, Lb. fermentum
,
Lb. pontis
,
and
Lb. reuteri
are commonly found in type II wheat and rye sourdoughs. Type III
sourdoughs are prepared in dried form to be used as nonliving acidifier supplement
and flavor carriers for (sourdough) bread production. In contrast to type I doughs,
doughs of types II and III require the addition of baker's yeast for leavening.
Commercially available bulk starter cultures to prepare type II and III sour-
doughs aim at standardizing the end products through acidification of and flavor
formation in the dough [
69,
181,
182
]. New trends tend to develop starter cultures
that lead to improved functional properties other than acidification and flavor for-
mation, such as texture improvement, antibacterial and antifungal activities, and
