Biomedical Engineering Reference
In-Depth Information
pentosaceus
, which are not frequently isolated in conventional sourdoughs, were
present in various GF sourdoughs, in particular when produced by spontaneous fer-
mentation. The pseudocereals buckwheat and amaranth were found to be good sub-
strates for the growth of
L. sakei
,
P. pentosaceus
and
L. paralimentarius
, whereas
buckwheat sourdoughs induced inhibition of yeast growth [
46,
47,
50,
51
] . In con-
clusion, the ecological studies on GF fermentations suggest that GF flours represent
an important reservoir for novel, competitive LAB and yeast strains that can be
selected as starters for the production of stable GF sourdoughs. In a second stage,
these strains can be screened for their functional properties, such as production of
EPS, aroma and/or anti-fungal compounds and rate of acidification [
5,
72,
74
] .
10.4
Proteolysis as a Tool to Improve the Baking
Performances of GF Flours
The proteolytic events occurring during sourdough fermentations of wheat and rye
flours have been exhaustively reviewed by Gänzle et al. [
75
] . Protein degradation
during sourdough fermentation is among the key phenomena that affect the overall
quality of sourdough bread, by inducing formation of precursors for flavour com-
pounds and by modifying the viscoelastic properties of the dough [
75
] . Because of
the gradual acidification of the dough by LAB, endogenous enzymes are activated
and exert primary proteolysis on flour proteins. In a second stage, the released pep-
tides are further hydrolysed into amino acids by intracellular peptidases of LAB, in
a strain-speci fi c manner [
76
]. In general, most sourdough LAB do not possess extra-
cellular proteinase activity and prefer peptide uptake over amino acid transport [
77
] .
LAB can affect the pattern of hydrolysed products by increasing the amount of
dipeptides and amino acids released in the sourdough ([
76
,
77
] . As yeasts consume
amino acids during growth, amino acid accumulation in sourdough can occur only
after yeast growth has stopped [
78-
80
]. Studies on the proteolytic events occurring
during sourdough fermentation of GF flours and their effects on GF bread quality
are still limited. Recently, sourdough fermentation was effectively applied for the
production of GF bread based on sorghum flour, potato starch and HPMC ( [
48
] ;
Table
10.1
). Superior quality bread could be produced only when the total amount of
sorghum flour was replaced by sorghum sourdough, fermented with the starter strain
L. plantarum
. The authors ascribed this quality improvement mainly to the prote-
olytic events occurring on soluble sorghum proteins during sourdough fermentation.
The hydrolysed proteins did not interfere with the starch gel upon gelatinisation and
a stronger starch gel with superior structural properties was obtained. As shown by
confocal laser scanning microscopy (CLSM), the presence of small peptides in the
sourdough bread prevented the formation of protein aggregates in the crumb upon
cooking; whereas aggregates were formed in the chemically acidified control.
Elkhalifa et al. [
81
] investigated the molecular and structural changes occurring
during fermentation of sorghum flour for the preparation of the traditional Sudanese
food
kisra
. As shown by light and CLS microscopy, fermentation resulted in the
