Biomedical Engineering Reference
In-Depth Information
10.6
Exopolysaccharides: A Low-Cost Alternative
to Hydrocolloids in GF Breads
Exopolysaccharides (EPS) produced by LAB are alternative biothickeners that act
as viscosifying, stabilising, emulsifying or gelling agents in a wide range of food
products [
90
]. EPS are generally classified in two categories: homopolysaccharides
(HoPS), glucose or fructose polymers, and heteropolysaccharides, containing (ir)
regular repeating units [
90
]. To date, only HoPS have been shown to be useful in
bread making. Glucans and fructans are synthesised by extracellular glucan- or
fructansucrases, respectively, by various sourdough-associated LAB.
Lactobacillus
reuteri, L. panis, L. pontis, L. frumenti and L. sanfranciscensis
were shown to pro-
duce fructans (levan or inulin) and glucans (dextran, reuteran or mutan) [
91
] . In
particular,
Leuconostoc
spp. and
Weisella
spp. were proved to synthesise a large
variety of dextrans [
92,
93
]. The structure, molecular weight and the production
yield of HoPS varies among the producing LAB species and also depends on the
carbohydrate concentration and composition of the source [
92,
94
] . During sour-
dough fermentations, LAB can produce EPS in high amounts, sufficient for improving
the structural properties of the dough [
95,
96
]. In particular, in situ production of
EPS was shown to be more effective than external addition of the same polysac-
charide in the bread formulation [
97
]. Addition of sourdough fermented with HoPS-
producing strains in wheat dough had a dramatic effect on bread quality by inducing
softening of the crumb and increasing specific volume of the bread [
92,
93,
95
] .
In addition to EPS, glucan- and fructansucrase can synthesise gluco- and fructo-
oligosaccharides (FOS), respectively [
98
]. FOS have been associated with prebiotic
effects [
94
,
99
]. In particular, the levan produced by
L. sanfranciscensis
LHT2590,
was proved to stimulate bifidobacterial growth in vitro [
100
] . In sourdough,
L. reu-
teri
,
L. acidophilus
and
L. sanfranciscensis
LHT2590 showed the ability to produce
the prebiotic FOS 1-kestose [
94,
94
]. Therefore, EPS-producer strains can be applied
not only to improve the bread-making performance of the flour, but also to enhance
the nutritional value of the bread. These features render EPS the ideal replacement
for hydrocolloids in GF breads. However, to date, only few studies [
41,
52
] have
investigated EPS formation in GF sourdoughs and their feasibility for GF baking.
Schwab et al. [
52
] recently analysed the applicability of the EPS-producers
L. reuteri
LHT5448 and
W. cibaria
10M in GF sourdoughs (Table
10.1
). Both strains
were shown to be suitable starters for sourdough fermentation of quinoa and sorghum,
and during fermentation they produced levan/FOS and dextran/GOS (galacto-
oligosaccharides), respectively. When applied in baking, sorghum sourdough fer-
mented with
W. cibaria
was shown to be the most effective. In fact, softer sorghum
breads were obtained upon addition of this sourdough, and the isomaltooligosaccha-
rides present in the dough were not digested by baker's yeast during proofing [
52
] .
The authors concluded that consumption of 300 g of sorghum GF bread prepared
with
W. cibaria
10M would account for a significant intake of prebiotic GOS.
Galle et al. [
41
] have also screened EPS-forming
Weissella
strains for their potential
as starter strains in sorghum and wheat sourdoughs (Table
10.1
). Independent from
