Biomedical Engineering Reference
In-Depth Information
the strain used, higher amounts of EPS were formed in sorghum sourdough than in
wheat, because of the higher concentration of glucose in the GF flour. In particular,
the amount of dextrans produced by
W. kimchii
and
W. cibaria
MG1 were high
enough for the sourdough to be applicable as a replacement for hydrocolloids in
bread. In both sourdoughs,
Weissella
strains also produced oligosaccharides, whose
structure was dependant on the chosen flour. Furthermore, both strains released fruc-
tose and formed only small amounts of acetate, a characteristic which is favourable
for bread production [
101
]. All together, these studies indicate that sourdough fer-
mented with EPS-forming
Weissella
strains can be applied in GF bread as a substi-
tute for hydrocolloids. In addition, different types of oligosaccharides can be formed
in the GF sourdough through manipulation of the carbon sources.
In conclusion, EPS-forming LAB can be successfully applied for improving the
baking performances of GF flours. However, screening must be performed in order to
identify EPS-producing strains that can be successfully applied as starter cultures in
GF sourdoughs. In addition, more investigations are needed to evaluate the applica-
bility of specific starters in GF sourdough breads, as the type of EPS and its interac-
tions with the matrix strongly influence the structural properties of the dough [
93
] .
10.7
Starch Hydrolysis for Delaying the Staling of GF Bread
Retrogradation/recrystallisation of starch is one of the key events involved in bread
staling. During storage, the amylopectin network present in fresh bread gradually
turns into a semi-crystalline network, which is responsible for crumb firming [
102
] .
Amylases, in particular maltogenic amylases, and malt are commonly applied in
bread baking as anti-staling agents [
103
]. Addition of sourdough to wheat bread can
retard staling and sourdoughs with high TTA (total titratable acidity) and low pH are
favourable for such purposes [
104
]. Even if most LAB species do not possess
amylolytic activities, amylolytic strains were isolated from cereal fermentations in
tropical climates [
75,
105,
106
]. In this regard, Corsetti et al. [
107,
108
] showed that
the biological acidification together with the proteolytic and amylolytic activities of
the selected starter strains delayed staling of sourdough wheat bread.
Staling represents one of the major issues in GF baking, since most GF breads
are mainly starch based. Research on the effects of sourdough fermentation in starch
hydrolysis and staling in GF bread is extremely limited. Malting and boiling com-
bined with fermentation of sorghum resulted in a decrease of crumb firmness and
dryness of sorghum-wheat composite bread [
109
] . Songré-Ouattara et al. [
110
] iso-
lated amylolytic strains of
L. plantarum
in pearl millet gruels and efficiently used
them as starter cultures for starch hydrolysis. The authors also suggested that more
amylolytic strains can be isolated from the traditional product [
110
] . Schober et al.
[
48
] showed that the combination of a-amylase and sourdough improved the qual-
ity of sorghum bread, but it did not have any positive effects on the staling rate.
Instead, chemical acidification had rather negative effects on the bread volume and
it dramatically increased the firmness over the whole storage period. Incorporation
