Biomedical Engineering Reference
In-Depth Information
Table 4.1
Characteristics of sourdough bread versus baker's yeast bread (adapted from (
1,
2
) )
Characteristics
Sourdough bread
Baker's yeast bread
pH
3.8-4.6
5.3-5.8
Lactic acid
0.4-0.8%
0.005-0.04%
Acetic acid
0.10-0.40%
0.005-0.04%
Bread volume
0.22-0.30
£ 0.20
Flavour
Complex aroma and fl avour
Staling
Slow
Rapid
Shelf life
Good protection against microbial
contaminations
High sensibility to bacteria and
mould spoilage
Some nutritional
aspects
Optimal phytase activity and
hydrolysis of phytic acid
responsible for ion (Ca
2+
, Fe
2+
,
Mg
2+
etc.) binding
Low phytase activity, decalcifying
effect
Free amino acid concentration
increase
Free amino acid concentration
similar to that of flour
Decrease of glycemic index
The main role of lactic acid bacteria (mainly obligately and facultatively
heterofermentative lactobacilli) is in the acidification process while yeasts mainly
account for the leavening of the dough by releasing CO
2
(
4
) .
4.2
Sourdough Preparation and Storage
Sourdough (mother sponge) preparation can be fulfilled through many different
protocols. The main objective is to obtain a leavening agent that contains well-
adapted resident microorganisms. Such microorganisms have to produce sufficient
CO
2
to leaven the dough, and organic acids and other metabolites to provide rye
or wheat bread with good texture and sensory properties, and extended shelf life
(
3
). Two classical procedures, for example the French and American systems, are
discussed below.
4.2.1
The French System
Mother sponge preparation for obtaining the French “
pain au levain
” begins
with a quite firm wheat flour dough (dough yield, DY of 150-152, see Sect.
4.6.2
)
with addition of salt and malt. This dough undergoes a first fermentation step
lasting ca. 24 h. This corresponds to the early fermentative activity of flour-
resident yeast and lactic acid bacteria, which results in a low CO
2
and organic
acid release (
2
). The decrease of pH induces the activity of flour endogenous
proteases which together with bacterial hydrolytic enzymes act on gluten and
