Biomedical Engineering Reference
In-Depth Information
fermentation times at low temperature are used to increase the concentration of
acetic acid synthesized by the obligately heterofermentative
L. sanfranciscensis
.
Recently, a liquid San Francisco sourdough, which is stabilized through pasteuriza-
tion, has been introduced to the market. Thus, also the type III sourdough is used as
an acidifying and flavouring agent for the manufacture of the San Francisco bread
in ca. 3 h (no-time-dough process) (see Sect.
4.7
) (
12
) .
4.5
Stability of the Sourdough Microbiota During
Propagation and Use
In order to keep microorganisms active, type I sourdoughs are, generally, propa-
gated daily. Thus, problems of microbiota stability during propagation and in the
use of such a type of “biological starter” arise.
In general, it is recognized that in a sourdough ready to be used (e.g. the mother
sponge—see Sect.
4.2
) for bread and other baked goods production the following
basic characteristics occur:
-
The prevalence of a microbial community different from that of the flour used as
raw material (
3,
19,
20
) ;
A stable ratio among lactic acid bacteria and yeasts (to the order of 100:1 or
-
higher) (
7
) ;
A predominance of facultatively and, especially, obligately heterofermentative
-
lactobacilli over other lactic acid bacteria (
3
) .
As reported by Vrancken et al. (
21
), laboratory sourdoughs based on wheat,
rye, or spelt that are backslopped daily, reach equilibrium through a three-step
process: (1) prevalence of sourdough-atypical lactic acid bacteria, (2) prevalence
of sourdough-typical lactic acid bacteria, and (3) prevalence of highly adapted
sourdough-typical lactic acid bacteria (
21
). In a recent paper dealing with the
comparative analysis of seven mature sourdoughs of type I backslopped for
80 days at artisan and laboratory levels under constant technological parameters,
Minervini et al. (
22
) showed that, while the cell density of presumptive lactic
acid bacteria and related biochemical features were not affected by the environ-
ment of propagation, all sourdoughs harboured a certain number of species and
strains, which were dominant throughout time and, in several cases, varied
depending on the environment of propagation (
21
) . Moreover, besides stable
species and strains, other lactic acid bacteria temporarily contaminated the sour-
doughs with differences between artisan and laboratory levels. Interestingly, this
occasional succession of strains and species only slightly affected the kinetic of
sourdough acidification; nevertheless, it could influence the sensory properties
of the resulting leavened baked product. Overall, as a stable microbiota during
sourdough propagation and use is essential in order to obtain standard and repeat-
able final products, the problem of microbial stability in terms of species and
