Biomedical Engineering Reference
In-Depth Information
cross-linking, resulting in a decreased molecular weight of the glutenin macropoly-
mer (GMP). Only small amounts of reducing agents are necessary to strongly affect
the disulfide network of glutenins [
40
] .
8.5
Exopolysaccharides
Some strains of LAB synthesize EPS from sucrose. EPS exhibit a positive effect on
the texture, mouthfeel, taste perception, and stability of fermented food. Moreover,
prebiotic effects have been described for specific EPS [
41-
43
] .
EPS can be classified in homopolysaccharides (HoPS) and heteropolysaccharides
(HePS) on the basis of their biosynthetic pathways. HoPS are synthesized from
sucrose by extracellular glucansucrases or fructansucrases and contain only one
type of monosaccharide, glucose or fructose, respectively. HePS are synthesized by
intracellular glycosyltransferases and consist of one or several monosaccharides
(see Chap.
7
). HePS formation by LAB is used in dairy fermentation to improve the
texture of yoghurt and other fermented dairy products, but was recently also
employed in sorghum sourdough fermentation [
44
]. Glucan and fructan synthesis
was observed for
Leuconostoc
spp
.
and
Weissella
spp., which synthesize dextrans
[
45
] .
Lactobacillus reuteri
,
L. panis
,
L. pontis
,
L. frumenti
,
and L. sanfranciscensis
produce fructans (levan or inulin) and glucans (dextran, reuteran, or mutan) [
43
] . It
was reported that any sourdough is likely to contain at least one EPS-producing
strain [
43,
46
]. In addition to EPS, glucan and fructansucrases can synthesize gluco-
and fructooligosaccharides, respectively. In sourdough
L. reuteri
,
L. sanfranciscen-
sis
and
Weissella cibaria
were shown to synthesize FOS, 1-kestose, and
isomaltooligosacchrides, respectively [
47-
49
]. Together with EPS, in particular
levan from
L. sanfranciscensis
, oligosaccharides have been described for their
beneficial health effects. The production of EPS by sourdough LAB exerts two dif-
bread texture.
Bacterial HoPS in sourdough act as hydrocolloids. The effect of bacterial EPS and
hydrocolloids on dough and bread is based on two functions: (1) water binding at the
dough stage and (2) the interaction with other dough components such as proteins
and starch. This interaction influences structural networks during fermentation and
the baking process [
50
]. During sourdough fermentations, LAB can produce EPS in
amounts that are sufficient for improving the dough structure [
49
] . Dextran from
Leuconostoc
mesenteroides
was reported to contribute to the long storage stability of
Panettone [
51
]. The application of in situ formed EPS can therefore reduce the
requirement for hydrocolloids to meet the consumer demands for clean labels and
reduced costs. Furthermore, levan produced in situ was more effective compared to
externally added levan [
52
]. The technological benefits of in situ formed EPS depend
on EPS properties and polymer yield. These are in turn dependent on the carbohydrate
supply of the fermentation substrate. Depending on the strain, flour, dough yield,
and fermentation conditions can be selected to obtain optimal EPS production [
53
] .
