Biomedical Engineering Reference
In-Depth Information
be classified as type III. Especially liquid sourdough represents an advantage for
industrial applications because it can be pumped and easily dosed, while showing
constant quality (
12
). Generally, the use of a stabilized sourdough is quite simple. It
can be stored at room temperature for a long time (30-60 days) and directly added to
the final dough at a proportion of 5-10%. Because of the low cell density of lactic
acid bacteria and yeasts, baker's yeast is generally added to leaven the dough for
bread production. Examples of applications of type III sourdough in the modern
bakery industry are the use of a stabilized liquid rye sourdough for rye bread produc-
tion; dextran-containing sourdough (produced by the use of selected
L. mesenteroi-
des
strains) stabilized by cooling, pasteurization, or drying for the production of
Panettone, rye bread and toast bread; pasteurized San Francisco sourdough in liquid
form for the production of San Francisco bread (
12
) .
The selection of microbial strains represents the current challenge for sourdough
bread-making industries and relies on several metabolic traits which are related to
the most important flavour compounds. Overall, strains isolated from raw materials
or sourdoughs are in vitro and in situ selected and evaluated mainly based on the
kinetics of acidification, proteolytic activity and nitrogen metabolism and synthesis
of aromatic compounds. Recently, fermentation processes based on selected lactic
acid bacteria and liquid sourdough have been evaluated with the aim of improving
the biosynthesis of specific chemical compounds (
49
) .
4.8
Use of Pure Cultures of Sourdough Starters Versus
Stabilized Sourdoughs
As for other fermented food biotechnologies (dairy, oenology, meat) the interest in
using a commercial starter culture is rapidly increasing for sourdough breadmaking.
In this context, some researches have been devoted to the use of freeze-dried or
frozen preparations of lactic acid bacteria (
4,
20
) . Nevertheless, only a few applica-
tions of selected lactic acid bacteria starters are currently documented both at arti-
san and industrial levels. Difficulties are mainly related to the possibility of obtaining
highly concentrated lactic acid bacteria preparations as well as to the performance
of the selected lactic acid bacteria in situ. From an applicative point of view starter
cultures should be pre-cultivated in a mix of flour and water to obtain metabolically
active strains before use as an inoculum. Nevertheless, it has been found that many
strains, which were in vitro selected for interesting traits, show some difficulties in
dominating the sourdough ecosystem and overcoming the endogenous lactic acid
bacteria throughout refreshments. Recently, Siragusa et al. (
24
) demonstrated that, after
ten consecutive refreshments, only three out of nine
L. sanfranciscensis
strains,
which were in vitro selected for the optimal rate of acidification, proteolytic activity
and release of flavour compounds, were able to persist during sourdough fermenta-
tion due to the dominance of autochthonous
L. plantarum
strains. Thus, the capabil-
ity to adapt to the sourdough ecosystem seems to be an essential trait for selecting
strains in order to obtain a sourdough with a constant microbial composition and
