Biomedical Engineering Reference
In-Depth Information
an effective means to increase the bioaccessibility of ferulic acid. Wheat bread
supplemented with bioprocessed bran increased the in vitro and in vivo
bioaccessibility of phenolic compounds as well as the colonic end metabolite 3-phe-
nylpropionic in breads, and exerted anti-inflammatory effects ex-vivo [
93,
94
] .
9.4
Microbial Exopolysaccharides
Dietary non-digestible oligosaccharides (NDO) have been shown to modulate the
composition and activity of intestinal microbiota, and they may also exert health
benefits in humans by improving bowel function, prevention of overgrowth of
pathogenic bacteria through selective stimulation of non-pathogenic members of
intestinal microbiota and by increased production of short-chain fatty acids (SCFA)
[
95
]. Intestinal fermentation and health benefits of fructo-oligosaccharides, galacto-
oligosaccharides and xylo-oligosaccharides have been well documented in animal
and human studies [
96,
97
] . Recently, stimulation by isomalto-oligosaccharides
(IMO) of the growth of intestinal lactic acid bacteria in a rat model was also shown
by Ketabi et al. [
95
]. The relationship between diet, intestinal microbiota and host
nutrition is currently under active investigation, and the integration of the functional
analyses of gut microbiota and sourdough genomes and metagenomes may allow
for design of prebiotic molecules with specific functional properties [
98
] .
Microbes are able to produce a variety of polysaccharides. Exopolysaccharides
(EPS) are sugar biopolymers that are secreted by bacteria, microalgae and by some
yeasts and filamentous fungi. They may protect cells from external stress factors
such as desiccation and antimicrobial substances, and mediate interactions of cells
with surfaces and other cells, thus playing an important role, for instance, in biofilm
formation. EPS can be divided into capsular polysaccharides that are more or less
tightly bound on cells, and extracellular slime which cells excrete to their surround-
ing medium. EPS production can usually be detected on solid and liquid medium,
respectively, from a slimy or ropy colony appearance and from an increase in
medium viscosity. Microbial EPS vary greatly in mass; from ~10 kDa to 1-2 mDa.
On the basis of their chemical composition, all microbial EPS can be broadly divided
into homopolysaccharides (= Hops), consisting of only one monosaccharide type,
and heteropolysaccharides (= Heps), made of two or more different monosaccharide
units. Additionally, various inorganic or organic constituents may be attached. The
possible complexities of polysaccharide structures are almost infinite as, for instance,
even a disaccharide may be linked in eight different ways [
99,
100
] .
Lactobacilli from wheat and rye sourdoughs have been shown to produce EPS
[
9,
101
] , and especially gluco-oligosaccharides [
102
] and fructo-oligosaccha-
rides, which have prebiotic properties [
9
] . For example,
Lactobacillus sanfranci-
scensis
LTH2590 produced 0.5-1% levan (flour basis) during 24-h fermentation
in wheat and rye doughs [
101
] . Tieking et al. [
103
] studied the ability of seven
fructan- or glucan-positive LAB (
Lb. sanfranciscensis
LTH 2581 and 2590,
Lb.
frumenti
TMW 1.103, 1.660, 1.669,
Lb. pontis
TMW 1.675,
Lb. reuteri
TMW
