Biomedical Engineering Reference
In-Depth Information
et al. [
50
] investigated the adaptability of various LAB and yeast starter strains in
continuously propagated sourdoughs prepared from GF cereals and pseudocereals.
The authors concluded that some of the starter strains used could not persist over the
fermentation and their adaptability to the GF sourdoughs was strongly influenced
by the chosen flour. Unfortunately, because of the high number of different sub-
strates used, the authors could not identify the reasons for such variability. Moroni
et al. [
46
] recently investigated the development of buckwheat and teff sourdoughs
using commercial starters. The substrate used determined the persistence of specific
starter strains; whereas spontaneous species, originating from the flour, either out-
competed or co-dominated with the starter LAB and yeasts. The unique sugar com-
position of certain GF flours is a key factor in the selection of dominant species in
GF sourdoughs [
41,
46,
47
]. For example, when added as a starter strain,
Lactobacillus sanfranciscensis
failed to grow in sorghum sourdough due to lack of
maltose at the beginning of the fermentation [
41
]. Instead, the high glucose level in
sorghum sourdough favoured the growth and metabolic activities of
Weissella
spp.
[
41
] . Similarly,
Weissella cibaria
was found to be highly competitive in buckwheat
sourdough, in which the initial content of the monosaccharide was higher than that
of maltose [
46,
47
]. Furthermore, the high ratio glucose/maltose favoured the
coexistence of maltose positive yeasts and LAB in teff sourdoughs [
46
] . All together,
these findings suggest that the nature of the GF flours used for sourdough fermentations
has a strong impact in the selection of the dominant LAB and yeast strains.
Furthermore, these studies clearly indicate that commercial starters as such cannot
be efficiently used for the production of GF sourdough. In fact, the main criteria for
selecting useful starters are that the starter's strains must be highly adapted to the
GF substrate, dominate the fermentation and inhibit the growth of contaminant and/
or autochthonous strains [
67
] .
Ecological studies on GF sourdoughs are essential for developing GF starters, but
to date only few data are available (Table
10.2
). Most of these investigations have
been carried out on traditional products, mainly produced from maize, sorghum and
teff in tropical countries. These fermentation products were dominated by LAB spe-
cies that mainly overlapped with those frequently isolated in wheat and rye sour-
doughs [
68
] . In particular,
L. fermentum
,
L. reuteri
and
L. plantarum
were the ones
most frequently isolated (Table
10.1
). However, an interpretation of the results
obtained in these studies is difficult due to the inappropriate techniques used for spe-
cies identification, and to the non-sterile conditions under which the fermentations
were carried out. More recently, the species diversity of laboratory-scale and indus-
trial sourdoughs produced from different GF cereals and pseudocereals has been
investigated through integrated approaches of culture dependent and independent
techniques (Table
10.1
). These sourdoughs have either been developed using starter
cultures [
43,
46,
50
] or by spontaneous fermentation [
47,
49,
64,
65
] . As observed in
traditional products,
L. fermentum
,
L. plantarum
, and also
L. paralimentarius
were
present in virtually all the spontaneously and starter fermented GF sourdoughs from
rice, maize, buckwheat, teff and amaranth (Table
10.1
). Instead, the dominance of
the most common sourdough species
L. sanfranciscensis
and
L. pontis
was substrate-
specific. Species such as
L. gallinarum
,
L. graminis
,
L. sakei
and
Pediococcus
