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Prebiotics: Metabolism, Structure, and Function



Prebiotics are a type of functional food ingredient that positively modulates the gut microbiota, thus improving and maintaining health. However, information on prebiotic metabolism and uptake in the gut environment is currently scarce. One interesting research strategy is to look at prebiotic structures that influence such metabolism. Current prebiotics constitute a range of carbohydrate structures with varying effects on the populations of bacteria and metabolites produced within the colonic ecosystem. Advances in molecular microbiology techniques, such as 16S ribosomal ribonucleic acid sequencing and metagenomics approaches, are increasing our understanding of the complex gut microbiota and might enable us to develop novel prebiotics by predictive understanding of how specific carbohydrate structures are fermented by the gut microbiota. This review focuses on current understanding of prebiotic metabolism and structure-function relationships.
Prebiotics: Metabolism, Structure, and Function
Shahrul R. Sarbini, Robert A. Rastall, PhD
Prebiotics are a type of functional food ingredient that positively modulates the gut microbiota, thus improving and maintaining
health. However, information on prebiotic metabolism and uptake in the gut environment is currently scarce. One interesting
research strategy is to look at prebiotic structures that influence such metabolism. Current prebiotics constitute a range of
carbohydrate structures with varying effects on the populations of bacteria and metabolites produced within the colonic ecosystem.
Advances in molecular microbiology techniques, such as 16S ribosomal ribonucleic acid sequencing and metagenomics approaches,
are increasing our understanding of the complex gut microbiota and might enable us to develop novel prebiotics by predictive
understanding of how specific carbohydrate structures are fermented by the gut microbiota. This review focuses on current
understanding of prebiotic metabolism and structure-function relationships.
Key words: prebiotics, oligosaccharides, functional foods, gut health
It is increasingly being recognized that the composition
of the gut microbiota, as well as many of its physiologic
traits, can be modified by relatively small changes in the
diet, including the introduction of prebiotics to improve
or maintain host health. A dietary prebiotic is defined as ‘‘a
selectively fermented ingredient that results in specific
changes in the composition and/or activity of the
gastrointestinal microbiota, thus conferring benefit(s)
upon host health.’’
Differing from probiotics, where live
microorganisms are introduced to the gut, one advantage
of using prebiotics to modify gut function is that the target
beneficial bacteria are already commensal to the colon. As
a result, prebiotics are a practical and efficient alternative
approach to influence the gut microbiota.
Generally, the beneficial bacterial groups that serve as
targets for prebiotics are bifidobacteria and lactobacilli.
However, owing to our increasing understanding of the
gut microbiota, other bacterial genera that might be
beneficial have been suggested, for example, Eubacterium,
and Roseburia
owing to their butyrate-
producing properties. In addition, some species, for
example, Eubacterium ramulus,
contribute to other
important processes in the human gut by forming phenolic
acids from a range of flavonoids, including quercitin,
rutin, and luteolin.
However, more evidence is needed on
the physiologic properties of these bacterial groups.
Nevertheless, it is becoming more clear that prebiotics
causing such selective modification in gut microbiota
composition and/or activity(ies) induce beneficial physio-
logic effects beyond the colon, contributing toward
reducing the risk of both intestinal and systemic
Potential prebiotic oligosaccharides can be classified
according to their chemical properties and degree
of polymerization (DP). These include inulin-type
fructans, galacto-oligosaccharides, lactulose, isomalto-
oligosaccharides, lactosucrose, xylo-oligosaccharides, soy-
bean oligosaccharides, gluco-oligosaccharides, and pectic
oligosaccharides. However, most of the scientific data
(both experimental and human) on prebiotic effects have
been obtained using inulin-type fructans and the
galactans. Owing to past
and recent data,
of these food ingredients have been granted prebiotic
status by demonstrating the capacity to selectively
stimulate the growth of bifidobacteria and, in some cases,
lactobacilli, consequently producing favorable changes in
the gut microbiota composition.
Despite the interest in prebiotics and their application
to host health, limited information is available regarding
the metabolic pathways and enzymes responsible for
transport and catabolism. Knowledge of the fermentation
pathways and uptake mechanisms of such oligosaccharides
would facilitate the enhancement of prebiotic functionality
and, to some extent, design of carbohydrates targeted at
particular species of probiotic microorganisms. This
Shahrul R. Sarbini and Robert A. Rastall: Department of Food and
Nutritional Sciences, University of Reading, Reading, UK.
Reprint requests: Robert A. Rastall, Department of Food and Nutritional
Sciences, University of Reading, Whiteknights, PO Box 226, Reading, RG6
6AP, UK; e-mail:
DOI 10.2310/6180.2011.00004
#2011 Decker Publishing
Functional Food Reviews, Vol 3, No 3 (Fall), 2011: pp 93–106 93
review focuses on the functionality of the gut microbiota
in the context of metabolism of prebiotic oligosaccharides.
Structure-function relationships of prebiotics based on
current studies are also described.
Carbohydrate Metabolism
The main carbohydrate substrates for bacterial growth in
the intestinal tract are dietary nondigestible carbohydrates
that elude proximal small intestinal hydrolysis and
absorption. These include carbohydrates, such as resistant
starch and resistant dextrins; nonstarch polysaccharides
(eg, pectins, arabinogalactans, gum arabic, guar gum, and
hemicellulose); nondigestible oligosaccharides (eg, inulin-
type fuctans, galactans, mannans, raffinose, and stachyose);
undigested portions of disaccharides (eg, lactose); and
sugar alcohols (eg, lactitol and isomalt).
The overall
intake of nondigestible carbohydrate in a Western diet is
estimated between 20 and 30 g/d. Endogenous carbohy-
drates, primarily from mucins and chondroitin sulfate,
contribute about 2 to 3 g/d of fermentable substrate.
Resistant starch, nonstarch polysaccharides, most diet-
ary fibers, and some nondigestible oligosaccharides are
fermented by a wide range of colonic bacteria, even though
the degree of hydrolysis and fermentability varies.
However, some nondigestible oligosaccharides that enter
the colon are selectively fermented (eg, inulin-type
fructans and galactans) by a limited range of bacteria
(eg, bifidobacteria and lactobacilli).
These ingredients are
generally acknowledged as prebiotic oligosaccharides.
Bacterial groups most likely to ferment nondigestible
oligosaccharides in the colonic microbiota generally belong
to the genera Bacteroides,Bifidobacterium,Ruminococcus,
Eubacterium,Lactobacillus, and Clostridium, which are the
predominant saccharolytic organisms.
Although carbohydrates are the preferred energy source
for the gut microbiota, certain groups of microbes, such as
Streptococcus,Clostridium,Bacillus, and Staphylococcus, are
able to ferment proteins.
In addition, other bacterial
groups, such as clostridia and Bacteroides, may switch to
protein fermentation in the absence of carbohydrates.
Proteins reaching the colon are fermented to branched-
chain fatty acids such as isobutyrate, isovalerate, and a
range of nitrogenous compounds. In contrast to carbohy-
drate fermentations, which are beneficial to health by the
production of short-chain fatty acids (SCFAs), some of
the end-products of protein metabolism may be toxic to
the host, for example, ammonia, amines, and some
phenolic compounds.
Excessive fermentation of pro-
teins, especially in the distal colon, have been linked to
disease states such as colon cancer and inflammatory
bowel diseases,
which generally originate in this region.
Thus, it is favorable to alter the gut fermentation toward a
saccharolytic fermentation over a prolonged period of
time, especially more distal regions of the colon.
Metabolite Production
Carbohydrates in the colon are fermented to SCFAs,
mainly acetate, propionate, and butyrate,
and other
metabolites, such as electron sink products, including
lactate, pyruvate, ethanol, succinate, as well as the gases
, and H
SCFAs reduce the luminal pH,
which can suppress the growth of enteric pathogens
also influences intestinal motility
as they are rapidly
absorbed by the colonic mucosa and contribute toward the
energy requirements of the host.
Many of the health-
promoting effects attributed to prebiotic oligosaccharides
are at least partially due to their influence on the
production of SCFAs by the colonic microbiota.
Acetate is mainly metabolized in human muscle,
kidney, heart, and brain tissues. Meanwhile, propionate
contributes to the inhibition of cholesterol synthesis in the
liver and the regulation of adipose tissue deposition.
Butyrate, on the other hand, is mainly metabolized by the
colonic epithelium, where it serves as the major energy
substrate and as a regulator of cell differentiation.
It is
also acknowledged that butyrate plays a protective role
against colorectal cancer and colitis.
rectally administered butyrate reduces inflammation in
subjects with active idiopathic ulcerative colitis.
addition, in vivo studies on rats
and weaning piglets
fed with fructo-oligosaccharides (FOSs) showed that the
concentration of butyrate was markedly stimulated
together with an increase in bifidobacterial populations,
which may be due to cross-feeding (discussed below).
Degradation of energy-rich complex carbohydrates creates
opportunities not just for competition but also for
cooperation by metabolic cross-feeding, in that metabolic
products from fermentation of dietary prebiotics by one or
more bacterial species provide substrates to support the
growth of other populations. Such cross-feeding may
result in metabolic consequences that could not be
predicted simply from the substrate preferences of isolated
bacteria, underlining the importance of mixed cultures in
the evaluation of candidate prebiotics. Figure 1 shows
94 Functional Food Reviews, Fall 2011, Volume 3, Number 3
some of the major microbiologic relationships in the
colonic ecosystem.
Fermentation of carbohydrates, particularly by bifido-
bacteria, is a significant source of lactate, which can then be
used by other species to produce acetate, butyrate, and
Lactate generally does not accumulate in
healthy subjects; however, it does accumulate in certain gut
disorders, for example, ulcerative colitis, where concentra-
tions up to 100 mM lactate have been observed.
Low G+C
gram-positive bacteria and the gram-negative Bacteroidetes
are capable of producing lactate as one of several
fermentation products.
High G+C gram-positive
Bifidobacterium spp and lactic acid bacteria such as
Lactobacillus and Enterococcus spp produce lactate as a
major product.
Lactate is converted into propionate by
bacteria such as Veillonella sp and Megasphaera elsdenii,
which has been found in the gut of farm animals.
addition, other groups of human intestinal bacteria use the
acrylate pathway in the absence of carbohydrates and the
presence of lactate to convert lactate into propionate,
described for cluster IX bacteria such as M. elsdenii.
Conversion of lactate to butyrate and/or propionate
can occur in the mixed gut community, as shown by stable
isotopic tracer studies.
This explains why substrates
that promote bifidobacterial populations in vivo can also
be butyrogenic
when it is known that bifidobacteria have
never been reported to produce butyrate.
Bacteria have
been isolated from human feces that convert lactate and
acetate into butyrate.
Previously unknown butyrate-
producing colonic bacteria have been isolated in the past
These bacteria belong to clostridial cluster
one of the most abundant bacterial groups in
human feces.
Species such as Anaerostipes caccae,
Roseburia intestinalis, and Eubacterium hallii have been
shown to be efficient lactate and/or acetate conver-
A study on coculture of Anaerostipes DSM
14662 and Bifidobacterium longum BB536 in an enriched
culture medium containing starch as an energy source
demonstrated that lactate is the key substrate for the cross-
feeding mechanism.
During oligofructose degradation,
B. longum BB536 released significant amounts of free
fructose into the extracellular environment, which was then
used by A. caccae DSM 14662, a strain that was not able to
degrade the substrate itself, thus producing butyrate. Cross-
feeding is also observed as increased production of butyrate
by Roseburia sp strain A2-183 in coculture with
Bifidobacterium adolescentis L2-32. However, in pure
culture, Roseburia sp strain A2-183 is unable to use lactate
or grow on starch or FOSs. The butyrate production
observed in these cocultures is probably due to cross-
feeding of products released by partial hydrolysis of FOSs or
starch by enzymes from B. adolescentis, most likely small
FOSs or malto-oligosaccharides. Furthermore, in coculture
studies of B. adolescentis L2-32 on starch or B. adolescentis
DSM 20083 on FOSs, both with E. hallii, the Bifidobacterium
strain produces lactate, with E. hallii being responsible for
conversion of lactate into butyrate.
It was suggested that
the butyrate is produced through a butyryl-coenzyme A
(CoA):acetate-CoA transferase pathway, with use of (partly)
exogenous acetate.
Conversion of lactate into butyrate is influenced by
ambient pH. The pH of the proximal colon is below pH
Figure 1. Major components and
interactions in the human gut
Sarbini and Rastall, Prebiotics 95
6.0 as a result of active microbial fermentation of dietary
whereas the pH of more distal areas is
higher. Belenguer and colleagues demonstrated that
E. hallii uses lactate at pH 5.7 to 6.5.
E. hallii and its
relatives, which account for 4% of human colonic
may play a significant role in preventing lactate
accumulation in vivo.
In a wider context, these cross-
feeding mechanisms are likely to play a significant role in
the colonic ecosystem and contribute to the combined
bifidogenic/butyrogenic effect of prebiotics.
Substrate Use by Probiotic Microorganisms
Bifidobacteria and, to a lesser extent, lactobacilli are still
regarded as the main targets for prebiotic use
and are
widely recognized as exerting beneficial effects on human
However, other bacteria, such as clostridial
clusters IV, IX, and XIVa,
which have been reported to
account for up to 25% of the colonic microbiota,
have a role in colonic well-being via butyrate production.
In this section, some key studies of these bacterial groups
are reviewed, focusing on the use of available substrates.
Recently, through detailed in vitro kinetic analysis of
oligofructose degradation, it has been shown that substrate
breakdown by bifidobacteria is remarkably different
compared to bacterial species belonging to other gen-
Bifidobacteria degrade oligofructose in a
preferential way, according to fraction length, only
commencing the breakdown of a longer chain length
fraction when shorter fractions are depleted. By contrast,
nonbifidobacterial species exhibit simultaneous degrada-
tion of all fractions, disregarding chain length, often
combined with the release of large amounts of free fructose
into the fermentation medium.
This type of substrate
degradation by nonbifidobacterial species can be linked to
extracellular degradation, which is less efficient than
internal or cell wall–bound degradation in a highly
competitive ecosystem such as the lumen of the human
This may be the reason why bifidobacteria
capable of intracellular degradation can grow selectively on
either inulin or oligofructose.
A recent study by Falony and colleagues classified four
main clusters of bifidobacteria depending on their
metabolism of inulin-type fructans.
However, the
boundary of these clusters goes beyond species limits.
The first cluster (cluster A) is characterized as not able
to metabolize inulin-type fructans, which includes
Bifidobacterium bifidum and Bifidobacterium breve.
However, bacteria belonging to this cluster might benefit
indirectly from the fermentation of oligofructose and
inulin by other members of the gut microbiota, for
example, through increased monosaccharides becoming
available for cross-feeding in the colon as a result of
fructan degradation by other bacteria
and by competi-
tion through the lowering of intestinal pH.
B. bifidum strains have also been reported to play a
specific role in the human colon ecosystem as mucin
Previous studies confirm the poor growth of
B. bifidum monoculture on inulin-type fructans.
However, strain-to-strain differences in fructofuranosidase
production levels have been reported. Recently, it was
demonstrated that B. bifidum DSM 20082, which belongs
to this cluster, is able to degrade inulin.
Strains belonging to clusters B, C, and D share the
ability to degrade oligofructose.
Cluster B is composed
mainly of strains that demonstrate rapid preferential
degradation of short chain length oligofructoses that are
linked to cell-associated fructan degradation.
However, cluster C bifidobacteria reveal a nondiscrimina-
tive breakdown mechanism, which use all chain lengths
simultaneously. In some cases, an increase in the free
fructose concentration in the fermentation medium was
This degradation pattern has, up to now, been
reported only for nonbifidobacterial species and is
generally associated with extracellular oligofructose degra-
This capacity to partially degrade inulin, without
a chain length preference, could offer cluster C bifido-
bacteria an additional advantage to these strains for
survival in a highly competitive ecosystem such as the
human colon.
Cluster D bifidobacteria are character-
ized by rapid metabolism of fructose or oligofructose and a
lack of discrimination between preferential and nonprefer-
ential degradation mechanisms.
However, a minor
preference for fructose as an energy source is revealed by
analysis of metabolite production. Therefore, it is sug-
gested that strains belonging to cluster D have a combined
effect of the efficient fructose consumption displayed by
cluster B bifidobacteria while at the same time possessing
the ability to partially degrade inulin displayed by cluster C
bifidobacteria. This makes these bacteria particularly
promising as objects of study regarding the bifidogenic
effect of inulin-type fructans.
Competitive studies of bifidobacteria have been
performed in coculture fermentations with Bacteroides
In a medium for colonic bacteria with inulin as
the sole added energy source, the ability of the bifido-
bacteria to compete reflects phenotypical variation.
96 Functional Food Reviews, Fall 2011, Volume 3, Number 3
B. breve Yakult (cluster A), a strain that is unable to break
down oligofructose or inulin, was outcompeted by
Bacteroides thetaiotaomicron LMG 11262, a strain with
high ability to metabolize both oligofructose and inulin.
B. adolescentis LMG 10734 (cluster B), a strain that
degrades oligofructose (displaying a preferential break-
down mechanism) but does not grow on inulin, however,
is able to compete when oligofructose and short fractions
of inulin start to accumulate in the fermentation medium.
Bifidobacterium angulatum LMG 11039T (cluster C), a
strain that degrades all oligofructose fractions simulta-
neously and is able to partially break down inulin, was
competitive from the start of the fermentation, rapidly
using short fractions of inulin. Meanwhile, B. longum LMG
11047 (cluster D), which is able to rapidly consume free
fructose and oligofructose and to partially degrade inulin,
was the dominant strain in a coculture with B. thetaiotao-
micron LMG 11262. Taken together, these observations
indicate that distinct subgroups within the large intestinal
Bifidobacterium population can be stimulated by different
groups of inulin-type fructans, thus providing variation in
health-promoting effects. However, such coculture experi-
ments only demonstrate interaction of isolated bacterial
groups derived from the human colon, which does not
reflect the full complexity in vivo.
Although some insights on bifidobacterial use of FOSs
have been demonstrated, use mechanisms for lactobacilli
are still unclear. It is known that some, but not all,
lactobacilli are able to ferment FOSs.
Barrangou and
colleagues reported the presence of fructofuranosidase
responsible for the hydrolysis of FOSs in Lactobacillus
acidophilus encoded by an inducible operon associated
with an adenosine triphosphate (ATP) binding cassette
(ABC) transport system.
In addition, this study showed
that L. acidophilus is able to use both short- and long-chain
FOSs. Similarly, an ABC transport system was implied in
FOS use by Lactobacillus paracasei.
In addition, a variety
of L. acidophilus strains have been shown to use several
polysaccharides and other oligosaccharides, such as
arabinogalactan and arabinoxylan.
A study by Bringel and colleagues revealed that
Lactobacillus plantarum WCFS is able to ferment a large
range of carbohydrates, such as monosaccharides (glucose,
mannose, and galactose), disaccharides (sucrose, lactose,
and trehalose), and oligosaccharides (raffinose and mele-
Furthermore, it has been shown that L. plantarum
WCFS is able to survive through the stomach while
remaining active and persisting for more than 6 days in
the human intestinal tract.
The genetic basis for this
persistence was investigated, and it is apparent that a
number of genes encoding functions related to sugar
metabolism are induced in situ.
Clostridial Clusters IV, IX, and XIVa
The clostridial clusters IV, IX and XIVa Firmicutes
represent some of the most abundant bacteria in the
human colon, making up roughly 25% of the colon
These organisms include a broad group of
bacteria, including species of Faecalibacterium (cluster IV);
Megasphaera,Veillonella,Selenomonas, and Megamonas
(cluster IX); and Anaerostipes,Clostridium,Coprococcus,
Eubacterium,Roseburia, and Ruminococcus (cluster
Many of its members are reported to be major
butyrate producers in the colon.
Given that butyrate is
regarded as a key metabolite for maintenance of colonic
health, these clostridial clusters (especially clusters IV and
XIVa) could have an influence on human well-being and
might be considered targets for prebiotic dietary interven-
A predominant species within cluster IV is
Faecalibacterium prausnitzii (previously assigned to the
genus Fusobacterium). F. prausnitzii uses a wide range of
carbohydrate substrates, including starch and inulin, to
produce butyrate and lactate with an absolute requirement
for acetate in the growth medium.
A close relative of
F. prausnitzii,Subdoligranulum variabile,
is able to grow
on fucose but not starch, producing butyrate and lactate as
end-products. Another isolate belonging to this group is
Anaerotruncus colihominis,
which is also unable to use
starch to form butyrate and acetate. Cluster IV Firmicutes
also includes many ruminococci that are able to hydrolyze
complex carbohydrates and form acetate as a major
fermentation product. Some examples are Ruminococcus
bromii strains, which break down starch, and
Ruminococcus albus and Ruminococcus flavefaciens, which
degrade recalcitrant substrates, such as cellulose, by the
action enzyme systems organized as cellulosomes that are
presented on the bacterial cell surface.
Robert and
Bernalier-Donadille demonstrated the ability of five novel
Ruminococcus isolates from human feces to degrade
microcrystalline cellulose.
Clostridial cluster IX in the
human colon has been estimated to account for around
7% of the bacteria in fecal samples from healthy donors
using fluorescence in situ hybridization.
identified within this cluster are predominantly sacchar-
olytic, and some employ the acrylate pathway for
Sarbini and Rastall, Prebiotics 97
propionate formation. An example is M. elsdenii, a lactate
user that can produce propionate.
The enhancement of colonic butyrate production after
consumption of either oligofructose or inulin
clostridial clusters IV and XIVa
is attributed to cross-
feeding with bifidobacteria.
A. caccae and Roseburia
spp grow on short-chain oligosaccharides and monosac-
charides released by Bifidobacterium spp during fructan
degradation but are also able to use bifidobacterial end–
products, including lactate and acetate.
An example is
oligofructose degradation by Roseburia faecis DSM 16840,
R. intestinalis DSM 14610, and Roseburia inulinivorans
DSM 16841, which degrades all chain lengths with the
release of free fructose into the culture medium, a
breakdown pattern that is associated with extracellular
fructan degradation.
This may provide opportunistic
competitors, which are not able to degrade inulin-type
fructans, with a valuable source of energy.
High-performance anion-exchange chromatography
with pulsed amperometric detection (HPAEC-PAD)
analysis of inulin breakdown by R. inulinivorans DSM
16841 reveals a preference for even shorter fractions than
B. longum LMG 11047.
This ability of B. longum LMG
11047 to quickly use longer chain fractions of inulin than
R. inulinivorans DSM 16841 provides a competitive
advantage. In a wider sense, these studies suggest that
the stimulation of butyrate-producing clostridial cluster
XIVa bacteria
is an attribute of cross-feeding interac-
tions rather than primary fructan breakdown,
revealing the importance of primary fructan degraders
such as bifidobacteria, to be present in the colon.
addition, it has been shown that many organisms in
clostridial clusters IV, IX, and XIVa produce gases, mainly
and H
As a result, these bacteria are
responsible for an enhancement of gas production owing
to fructan fermentation through either cross-feeding or
direct degradation of inulin-type fructans.
fructan consumption has been reported to cause some
abdominal discomfort linked to increased gas production,
that is, flatulence and bloating.
Metabolism of Prebiotic Oligosaccharides
The mechanisms by which prebiotic oligosaccharides are
selectively metabolized by beneficial microorganisms of the
gut microbiota are still being clarified. Generally, there are
two paradigms of prebiotic metabolism by the gut
microbiota. The most documented concept is that probiotic
microorganisms possess cell-associated glycosidases, which
allow degradation of prebiotic oligosaccharides.
enzymes hydrolyze monosaccharides from the nonredu-
cing ends of oligosaccharides, which are then absorbed by
the probiotic rather than other microorganisms in the
mixed-culture community in the human colon. This
mechanism has been demonstrated in a study by Perrin
and colleagues, who found that probiotic microorganisms
such as Bifidobacterium infantis possesses cell-associated
b-fructofuranosidases that act by hydrolysis of mono-
saccharide from nonreducing ends to liberate monomeric
fructose molecules, which are then transported into the
Possession of such enzymes is thought to
confer a selective advantage on these bacteria when
growing in the presence of prebiotic oligosaccharides.
The second paradigm is the ability of probiotic
microorganisms to take up oligosaccharides and metabo-
lize them internally. This concept proposes the existence of
a specific transport system enabling probiotic microorgan-
isms to use oligosaccharides. One example of such
metabolism was demonstrated by Kaplan and Hutkins,
where fermentation of individual oligomers of fructans
indicated that L. plantarum and Lactobacillus rhamnosus
are capable only of metabolizing the trisaccharide and
tetrasaccharide fractions, whereas pentasaccharides are not
metabolized by these strains.
This observation suggests
that there are specific transport systems in these organisms
specific for trisaccharides and tetrasaccharides.
In the next section, we review studies on the transport
and metabolism of prebiotic oligosaccharides that have
been extensively researched, namely, inulin-type fructans
and the galactans.
Inulin-Type Fructans
Fructans or nondigestible FOSs are selectively fermented
by specific beneficial intestinal bacteria, such as
Bifidobacterium and Lactobacillus species, with concomi-
tant suppression of less desirable bacteria.
consumption rates of FOSs are increased for those bacteria
that possess the metabolic pathways necessary for FOS
There are two types of FOS, which differ
depending on their methods of preparation and mono-
saccharide composition. Both are commercially available
and widely used in food applications. The first type,
usually referred to as the GFn-type FOS, is enzymatically
produced from sucrose and consists of a glucose monomer
(G) linked by a-1,2 linkages to two or more b-2,1-linked
fructose units (F), forming a mixture of GF2, GF3, and
Another type of FOS, commonly known as
oligofructose, or FFn-type FOS, is produce by partial
hydrolysis of inulin using endoinulinase enzyme and is
98 Functional Food Reviews, Fall 2011, Volume 3, Number 3
characterized as having a DP varying from 2 to 10, with an
average DP of 4.
A variety of enzymes have been associated with microbial
levanase EC,
fructofuranosidase EC,
fructanase EC,
and levan biohy-
drolase EC
However, these enzymes are func-
tionally related and may be considered members of the
same b-fructosidase superfamily that incorporates mem-
bers of both glycosyl family 32 and glycosyl family 68.
All of these enzymes are involved in the hydrolysis of b-
D-fructosidic linkages to release free fructose. In bifido-
bacteria, cytoplasmic b-fructosidases that catalyze the
hydrolysis of FOS in B. adolescentis,Bifidobacterium
infantis,andBifidobacterium lactis have been isolated
and characterized.
The gene encoding b-
fructofuranosidase in B. lactis DSM10140 has been cloned
and expressed in Escherichia coli.
In addition, the
genome sequence of B. longum defined the presence of at
least seven regions coding for oligosaccharide transport
and metabolism.
The function of these oligosaccharide-
metabolizing pathways is to enable bifidobacterial species
to compete and persist in the colon, where nondigestible
oligosaccharides accumulate.
In L. acidophilus NCFM, the FOS metabolic pathway
is encoded by a multiple sugar metabolism (msm)
The msm operon encodes an ABC transport
system and a cytoplasmic b-fructosidase that mediate
FOS uptake for subsequent internal hydrolysis.
Expression of the operon is induced by sucrose and
FOS but not by glucose or fructose. Similarly, b-
fructofuranosidases from B. adolescentis,B. infantis,
and B. lactis also hydrolyze FOS internally.
and Hutkins showed that the uptake of FOS by
L. paracasei 1195 is mediated by an ABC transport
This system shows a preference toward GF2
and GF3, whereas limited GF4 is transported. In
addition, the transport system is specific for FOSs and,
possibly, other substrates with a b-fructose or b-type
sugar linked to a-glucose. FOS hydrolysis activity is
detected only in the extracts of FOS or sucrose grown
cells but deficient in cell-free culture supernatants,
intracellular b-fructofuranosidase. In addition, both
FOS transport and hydrolysis activities are repressed by
products of FOS and sucrose hydrolysis, glucose and
Saulnier and colleagues also found that
L. plantarum WCFS1 possesses a putative intracellular
b-fructofuranosidase and suggested that the small
GFn oligosaccharides are transported via the sucrose
transport system in L. plantarum WCFS1.
This strain
also has a preference toward GF2 and GF3 but limited
consumption of GF4.
In contrast, an alternative FOS metabolic pathway
relies on extracellular enzymes to hydrolyze FOSs that
include fructan b-fructosidase from Lactobacillus pentosus
and levan biohydrolases from Streptomyces exfoliatus and
Microbacterium laevaniformans.
Recent microarray
transcriptome analyses of L. paracasei revealed the
presence of a FOS metabolic pathway, encoded by the
fosE operon, that is composed of a cell wall–associated b-
fructosidase and a fructose/mannose phosphotransferase
The intracellular and cell wall fractions were
both examined, and b-fructosidase assays showed that the
FOS hydrolysis activity is present primarily in the cell
It was also found that cell wall–associated b-
fructosidase faces the extracellular side and, therefore,
catalyzes FOS hydrolysis externally.
In addition,
inactivation of the fosE gene in L. paracasei prevents use of
FOS (FFn type), inulin, levan, and sucrose as sole carbon
sources, indicating that the fosE operon is essential for
metabolism not only of FOS but also of other fructose-
containing carbohydrates.
Expression of the b-fructosidase is induced during
growth on FOS, inulin, and, to a lesser extent, sucrose and
fructose but not glucose. Similarly, the preferred substrates
are FOS of the FFn and GFn types, followed by inulin, and
there is minor activity with sucrose.
These results
indicate that this enzyme has a preference for oligosac-
charides with b-2,1 linkages. The FFn form of FOS is
composed of 75% fructose oligomers with an average DP
of 4 and does not contain a terminal glucose molecule;
thus, most of its chains have more fructosyl units per
oligomer. This finding explains preferential exohydrolysis
of FFn than the GFn form of FOS by b-fructosidase.
Furthermore, the lower activities observed for inulin
indicate a preference for intermediate short-chain oligo-
saccharides. Exohydrolysis activity of the b-fructosidase
results in hydrolysis of the GF4 and GF3 fractions in FOS
first, producing GF2, sucrose, and fructose. Sucrose and
fructose then accumulate gradually as the concentration of
GF2 decreases.
Another related strain, L. paracasei 8700,
could use short- and long-chain fractions of FFn FOS
simultaneously, although when the organism is grown on
inulin and FOS, the FFn chains are preferred.
sucrose, and various FFn and GFn oligosaccharides are also
formed during growth on FOS and inulin, indicating that
an enzyme capable of extracellular hydrolysis is present in
this organism.
Metabolism of FOS through either of
these two metabolic pathways can be viewed as a benefit
Sarbini and Rastall, Prebiotics 99
that promotes cross-feeding by providing access to the
hydrolysis products for other beneficial intestinal micro-
organisms that do not possess the FOS transport metabolic
It is known that most bifidobacteria and, to some extent,
lactobacilli and other limited strains from other genera of
human intestinal origin readily use galacto-oligosacchar-
Studies demonstrate that two probiotic strains,
B. lactis DR10 and L. rhamnosus DR20,
use galacto-
oligosaccharides to support their growth in vitro.
There are two different metabolic pathways for lactose
use in lactic acid bacteria.
The first pathway involves the
phosphoenolpyruvate-dependent lactose phosphotransfer-
ase system that results in the uptake of lactose into cells as
lactose-6-phosphate. This is hydrolyzed by phospho-b-
galactosidase into glucose and galactose-6-phosphate for
further metabolism.
Most of the lactococci employ this
pathway for the metabolism of lactose.
The second known pathway for the uptake of lactose in
lactic acid bacteria involves a specific lactose permease that
transports lactose from the growth medium into the
cytoplasm of the bacteria. Lactose is then hydrolyzed into
glucose and galactose by intracellular b-galactosidase.
study by Prasad and colleagues comparing B. lactis DR10
and L. rhamnosus DR20 using galacto-oligosaccharides
demonstrated that the strain B. lactis DR10 preferentially
uses oligosaccharides with higher degrees of polymeriza-
tion, that is, trisaccharides and tetrasaccharides; how-
ever, L. rhamnosus DR20 prefers monosaccharides and
Surprisingly, monosaccharides, includ-
ing glucose, are the last sugars to be used by B. lactis
DR10. These observations indicate that the two strains
possess different uptake systems for the use of galacto-
oligosaccharides. The fundamental differences between
these two pathways relates to lactose transport across the
membrane, with different marker enzymes, that is,
phospho-b-galactosidase for B. lactis DR10 and b-
galactosidase for L. rhamnosus DR20.
Structure-to-Function Relationships of Prebiotics
Although many recent studies on prebiotics have focused on
health benefits, limited knowledge is available regarding
structure-function relationships in prebiotic carbohydrates.
Nevertheless, some studies have been undertaken with the
long-term view of enhancing prebiotic efficacy and, to some
extent, specific health functionality. In this section, we
review key studies on prebiotic oligosaccharides regarding
structural comparisons that may be influenced by mono-
saccharide composition, glycosidic linkage, and molecular
Monosaccharide Composition
Sanz and colleagues investigated the effect of monosac-
charide composition on a wide range of disaccharides on
the fermentation selectivity of gut bacteria.
For a-
linkages, glucosyl-glucose presents greater selectivity than
galactosyl-galactose. However, for b-linkages, the behavior
is the opposite. Apart from a-1,4 linkages, fructose-
containing disaccharides display lower selectivity than
glucosyl-glucoses or galactosyl-galactoses.
Glycosidic Linkages
Sanz and colleagues also investigated the influence of
glycosyl linkage on fermentation selectivity.
disaccharides with a-1,2 linkages (kojibiose and sophor-
ose) result in the highest bifidobacterial populations.
Olano-Martin and colleagues demonstrated that fermenta-
tion selectivity of oligodextrans, a-1,6 glucans, is higher
than maltodextrins, a-1,4 glucans.
b-1,4 linkages are
cleaved more slowly by b-galactosidase of B. bifidum
compared to b-1,3 and b-1,6 linkages.
The b-1,3 and b-
1,6 linkages have also been described as being more
selective for bifidobacteria.
There are currently very few reliable data on the
digestibility of candidate prebiotic molecules as this is a
very challenging property to determine and requires large
quantities of carbohydrates. However, some data are
available. Starch modified with a- and b-amylase to
increase a-1,6 relative to a-1,4 linkages leads to slower
Branched glucan a-1,2 glycosidic linkages
produced by Leuconostoc mesenteroides NRRL B-1299
result in a very high resistance to hydrolysis by digestive
enzymes in both humans and animals, making this type of
glucan an interesting candidate prebiotic.
Molecular Weight
Our current understanding of prebiotic substances is that
low-molecular-mass oligosaccharides are more rapidly and
more selectively fermented by bifidobacteria and lactoba-
cilli than high-molecular-weight carbohydrates. This
property may be due to the fact that the low molecular
mass means more nonreducing ends per unit mass, which
favors attack by exo-acting enzymes produced by
100 Functional Food Reviews, Fall 2011, Volume 3, Number 3
Bifidobacterium spp.
A recent comparison study of
inulin-type fructans of varying chain length showed that
shorter-chain oligosaccharides are more rapidly fermented
and produce higher proportions of butyrate when
compared to longer-chain inulin.
These results, how-
ever, contradict previous reports that longer-chain inulin
produced higher proportions of butyrate than shorter-
chain FOSs.
Differences in fermentation models or in
the microbiota may contribute to these conflicting results.
Also, butyrate production by FOSs is primarily caused by
acetate-butyrate conversion.
The DP appears to be a
determining factor in Bifidobacterium metabolism of FOSs.
Generally, as chain length increased, consumption by
bifidobacteria decreased.
Conversely, the longer DP of
inulin leads to slower digestion, with inulin reaching more
distal regions of the colon.
Therefore, it is important to
determine the optimal molecular weight to achieve
beneficial health characteristics. Many of the data available
on the influence of molecular mass derive from in vitro
experiments in model systems, and there is a need for in
vivo research in humans.
A desirable approach to the development of candidate
prebiotics with controlled molecular weight profiles is the
enzymatic modification of plant cell wall polysaccharides.
Xylan, although recognized as a dietary fiber, is not
fermented well by lactobacilli and bifidobacteria,
whereas xylo-oligosaccharides are used by bifidobacteria
and lactobacilli.
Using wheat arabinoxylans, Hughes
and colleagues found that the selectivity for bifidobacteria
and lactobacilli increases as the molecular mass
A similar situation has been found with glucan-based
oligosaccharides. Olano-Martin and colleagues demon-
strated that lower DP oligodextrans produced by con-
trolled enzymatic hydrolysis result in higher fermentation
selectivity for bifidobacteria compared to the parent
dextran molecule and other oligodextran fractions with a
higher average DP.
However, higher-molecular-mass
oligodextrans exhibit greater persistence through an in
vitro three-stage continuous culture system.
and colleagues showed the influence of DP with related
isomalto-oligosaccharides on human fecal bifidobacteria,
with a DP of 3 giving higher prebiotic activity than a DP of
In addition, using in vitro batch cultures, maltose-
based oligosaccharides with a DP of 3 result in the highest
selectivity toward bifidobacteria, with a DP of 6 or 7 also
being selective. However, oligosaccharides with a DP .7
are not selective for bifidobacteria.
Different fractions of
gentio-oligosaccharides and alternansucrase gentiobiose
acceptor products (AGOS, Alternansucrase Gentiobiose
Oligo Saccharides) were also studied for their selectivity in
Gentio-oligosaccharides with a DP of 2 or 3 are
the most selectively fermented, whereas for the AGOS,
oligosaccharides with a DP of 4 or 5 are the most selective.
The highest levels of butyrate are seen from the AGOS of a
DP of 6 to 10. The a-linkages present in AGOS fractions
likely contribute to the increased selectivity compared to
gentio-oligosaccharides with a similar molecular weight.
Prebiotics have much potential as functional food
ingredients to either improve or maintain a balanced
optimal intestinal microbiota composition with the aim of
enhancing overall health and well-being.
This has been
shown frequently over the last two decades, and data
continue to accumulate, improving our understanding of
the gut microbiota. Understanding of the relationships
between prebiotic-induced changes in gut microbiota
composition and/or activities and health consequences is
increasing. To date, most available data concern the
selective stimulation of beneficial bacterial groups, such as
bifidobacteria and lactobacilli. Such changes in the
composition of the fecal microbiota, especially increases
in bifidobacteria, can be regarded as markers of intestinal
Current understanding of the gut microbiota is largely
at the level of microbial genera or groups. With increasing
use of molecular microbiologic techniques, it will be
possible to gain definitive information on individual
species influenced by specific carbohydrates. The genetic
basis of fermentation of prebiotics in bifidobacteria and
lactobacilli is being unraveled, and this is of importance
because certain species of bifidobacteria or lactobacilli
may be more desirable than others; that is, it is
improbable that all bifidobacterial and lactobacilli species
colonizing the colon have similar health-promoting
properties. Consequently, measuring changes at a group
level may not be sufficiently informative. Genome
sequencing of a wide range of intestinal isolates and
metagenomic studies is yielding valuable information on
the structure and metabolic potential of the colonic
microbial community. Detailed profiling of such isolates
with respect to substrate use, together with in vitro and in
vivo microbial ecology studies, will provide a sound
understanding of the impact of diet on the gut
microbiota. Such studies will lead to the discovery of
new candidate probiotic strains and prebiotic carbohy-
drates. Putatively beneficial genera, such as Roseburia and
Sarbini and Rastall, Prebiotics 101
Eubacterium, which are known butyrate producers, merit
As we obtain better information on the structure and
function relationships in prebiotics, coupled with increas-
ing knowledge of the metabolic profiles of target bacteria
within the gut microbiota, we will move into an era of
rational design of functional food ingredients targeted at
promoting gut health and overall well-being.
Financial disclosure of authors and reviewers: Robert Rastall
has several confidential research agreements with food
companies. None of which have influenced the contents of
this article.
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... 31 In detail, Bifidobacterium degrades oligofructose preferentially, according to fraction length, only commencing the breakdown of a longer chain length fraction when shorter fractions are depleted. 32 Hence smaller monomer residues in the pith of sago trunk are preferable for the colonic fermentation of Bifidobacterium spp., in which hydrolysable starch of sago palm stands constitutes 18-20% of the total organic content upon harvesting of palm hearts. 33 Lactobacillus-Enterococcus also increased after 6 h of fermentation in all samples. ...
... Generally, the clostridial bacteria make up roughly 25% among the colon microbiota. 32 Similar to the nutrient requirement of Bifidobacterium spp. and Lactobacillus spp., the Clostridium group is also more likely to utilize carbohydrates, especially oligosaccharides, as fermentation substrates. ...
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Background: Edible palm hearts (EPH) or known as palmito, chonta or swamp cabbage in America countries, or "umbut" in Malaysia is a type of vegetable harvested from palm tree species. The EPH is appeared firm and smooth and described to have a flavor resembling the artichoke which have underlying prebiotic potential that selectively stimulate the growth and activity of beneficial colonic microbiota, thus enhancing the host's health. This study is the first to present results of EPH from local species such as oil palm (Elaeis guineensis), sago palm (Metroxylon sagu) and coconut (Cocos nucifera) using in vitro colonic fermentation with human faecal. Samples obtained at 0, 6, 12 and 24 hours were evaluated by bacterial enumeration using fluorescent in situ hybridisation (FISH) and short-chain fatty acid (SCFA) by High-Performances Liquid Chromatograph (HPLC). Results: All EPH samples revealed induction effects towards Bifidobacterium spp., Lactobacillus-Enterococcus and Bacteroidaceae/ Prevotellaceae populations similar to those in inulin fermentation. Significant decrease (p ≤ 0.05) in pathogenic Clostridium histolyticum group was observed in the response of raw sago palm hearts. In general, all samples stimulate the production of SCFA. Particularly in the colonic fermentation of sago palm heart, the acetate and propionate revealed the highest concentration of 286.18 mM and 284.83 mM in raw and cooked form respectively. Conclusion: This study concluded that edible palm hearts can be a potential prebiotic ingredient that promotes human gastrointestinal health, as well as discovering a new direction towards an alternative source of functional foods. This article is protected by copyright. All rights reserved.
... Total bacteria counted using TPC method was calculated using the equation from Soesetyaningsih & Azizah (2020) by only putting the colony in the range of 30 to 300 colonies, and the value is 2.01 x 10 6 CFU/ mL. Prebiotics can alter the gut microbiota thus affected the host health (Sarbini & Rastall, 2011) and contribute to promote the growth of Bifidobacteria and Lactobacilli (Connolly et al., 2010). Thus, based on our result, corn cob can support the growth of Bifidobacterium longum and can be used as an alternative prebiotic. ...
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Corn cob is one of the most common agricultural wastes in Indonesia with high content of xylan. Xylan can be used to produce xylitol which cannot be digested by human digestive enzymes thus, make it a potential candidate of prebiotic. This preliminary research aimed to study the potency of corn cob in supporting the growth of Bifidobacterium longum. Corn cob was produced into powder and used as the carbon source in the growth medium of B. longum. Total plate count method was done to count the growth of B. longum in various concentrations of bacteria solution. The result showed that crude corn cob powder can support the growth of B. longum from bacterial enumeration with the value of 2.01 x 106 CFU/mL. The study indicated that corn cob has a potential to be used as prebiotic.
... Lactate concentration increased over the entire fecal fermentation for both microbial-FOS and Raftilose ® P95. These results are explainable via the aforementioned cross-feeding processes since lactate (already produced by other bacteria) can also be used as a substrate by bacteria producers of butyrate and propionate [16,22], preventing lactate accumulation and excess acidity [9]. Lactate levels were not detected after 72 h in a recent study by Liu et al. [52], corroborating the obtained results. ...
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The prebiotic potential of fructo-oligosaccharides (microbial-FOS) produced by a newly isolated Aspergillus ibericus, and purified by Saccharomyces cerevisiae YIL162 W, was evaluated. Their chemical structure and functionality were compared to a non-microbial commercial FOS sample. Prebiotics were fermented in vitro by fecal microbiota of five healthy volunteers. Microbial-FOS significantly stimulated the growth of Bifidobacterium probiotic strains, triggering a beneficial effect on gut microbiota composition. A higher amount of total short-chain fatty acids (SCFA) was produced by microbial-FOS fermentation as compared to commercial-FOS, particularly propionate and butyrate. Inulin neoseries oligosaccharides, with a degree of polymerization (DP) up to 5 (e.g., neokestose and neonystose), were identified only in the microbial-FOS mixture. More than 10% of the microbial-oligosaccharides showed a DP higher than 5. Differences identified in the structures of the FOS samples may explain their different functionalities. Results indicate that microbial-FOS exhibit promising potential as nutraceutical ingredients for positive gut microbiota modulation.
... By mass, members of the human microbiota constitute less than 0.5% of the overall bodyweight, yet are estimated to outnumber the cells of our body [1]. Directed by the function of upwards of 3,000,000 distinct genes from more than a thousand detected bacterial species [2], complex mechanisms of the microbiota act in a host co-dependent manner to shape the immune system [3] and regulate gut-brain crosstalk [4,5] and metabolism [6,7]. Diverse microbes inhabit human tissues, ranging from symbiotic commensals through opportunistic pathobionts to pathogenic species. ...
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Despite their ubiquitous presence in biological systems, glycans have historically received less attention than they deserved. Investigations in recent years have featured important findings about the role of glycans in regulating the human gut microbiota. Here, we present a brief overview of current trends that shape future directions of computational and experimental research approaches and add to our understanding of host–microbe glycointeractions.
... Moreover, diet is an important modulator of the gut microbiota, which is related to systemic inflammation. Fermentation of dietary fibres in the large intestine involves metabolic crossfeeding wherein the fermentation product of one or more species of bacteria provides a substrate for other species, producing SCFA, particularly acetate, propionate and butyrate (21,22) . These SCFA have several metabolic functions, such as reducing inflammation, increasing barrier function and down-regulating proinflammatory mediators that induce lipopolysaccharides (23) . ...
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Frailty, a multifactorial ageing-related syndrome characterized by reduced resistance to stressors and possibly associated with low-grade systemic inflammation (LGSI), results in negative health outcomes and compromises healthy ageing. There is a growing body of evidence on the relationship between dietary habits, LGSI and the risk of frailty. Consumption of dietary ultra-processed products (UPP) could negatively contribute to these conditions. In this article, we intend to: (i) discuss the role that ultra-processed food products (UPP) might have on the development of frailty considering the inflammatory potential of this type of food; and (ii) to raise awareness on deleterious effects of excess UPP intake in development of adverse health outcomes, in particular, frailty and compromised healthy ageing. UPP are industrial formulations whose nutrient profile has been associated with inflammation and altered gut microbiota. Besides, diets with a greater presence of unprocessed foods and antioxidants have been linked to the reduction of oxidative stress and the expression of inflammatory biomarkers. Because inflammation is believed to be a contributing factor in the development of frailty, it is possible that UPP would contribute to the onset or increase of this condition. Importantly, the increasing consumption of UPP in younger populations might pose a greater risk to the development of compromised healthy ageing in the long term.
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Culinary spices and herbs have been used in food and beverages to enhance aroma, flavor, and color. They are rich in phytochemicals that provide significant antioxidant and anti-inflammatory effects. There is growing interest in identifying compounds from spices and herbs responsible for modulating oxidative and inflammatory stress to prevent diet-related diseases. This contribution will provide an overview of culinary spices and herbs, their classification , their sources or origins and more importantly, their chemical composition, antioxidant activity and their impacts on human health based on important and recent studies.
Objective: To investigate the effect of oligosaccharides on the markers of glycemic control, including fasting blood glucose (FBG), fasting blood insulin (FBI), glycated hemoglobin (HbA1c), homeostasis model assessment of insulin resistance (HOMA-IR), and quantitative insulin sensitivity index (QUICKI). Methods: PubMed, Embase, and the Cochrane Library databases were systematically searched to find randomized controlled trials (RCTs) on the effect of oligosaccharide intervention on FBG, FBI, HbA1c, HOMA-IR, and QUICKI up to 7 June 2021. Data were pooled using weighted mean difference (WMD) and 95% confidence intervals (95% CI), with a p-value ≤0.05 indicating statistical significance. Risk of bias was assessed with the Cochrane tool and the quality of the literature with the new Jadad scale. Results: A total of 46 randomized controlled trials were included. Oligosaccharides significantly reduced FBG (WMD: -0.295 mmol L-1; 95% CI: -0.396 to -0.193; p < 0.001; I2 = 90.9%; 46 trials; 2412 participants), FBI (WMD: -0.559 pmol L-1; 95% CI: -0.939 to -0.178; p < 0.01; I2 = 99.1%; 29 trials; 1462 participants), HbA1c (WMD: -0.365; 95% CI: -0.725 to -0.005; p < 0.05; I2 = 86.6%; 11 trials; 661 participants), and HOMA-IR (WMD: -0.793; 95% CI: -1.106 to -0.480; p < 0.001; I2 = 96.1%; 24 trials; 1382 participants). Oligosaccharides were more beneficial for the participants with obesity or diabetes than for healthy participants. Multiple interventions per day consolidated the effectiveness of oligosaccharides. Regardless of the processing manner (starch-modified or naturally extracted) of the oligosaccharides, their intervention was overall beneficial for the patients with diabetes. Conclusions: This study is by far the most extensive systematic review to evaluate the role of oligosaccharides on the markers of glycemic control. Oligosaccharide interventions can exert beneficial effects on FBG, FBI, HbA1c, and HOMA-IR.
Over the past few decades, with the increase in consumer awareness about their health beneficial properties, there has been a considerable demand for probiotics, prebiotics and synbiotics and this has become the thrust area of research. These supplements have been termed as functional foods, as they are known to modify and stimulate the gut microflora and facilitate smooth functioning of the intestinal environment, thus conferring various beneficial effects on the health of the host. The most commonly used probiotics are Bifidobacterium, Lactobacilli , and Bacillus coagulans ; prebiotics include galactooligosaccharides, fructooligosaccharides, inulin, etc. Probiotics and prebiotics when used together are known as synbiotics and impart additional health benefits on the host. Thus, in the present context, the chapter gives detailed information about probiotics, prebiotics and synbiotics, their possible mechanisms and the potential health applications on the host. In addition, the current scenario and the challenges of synbiotics are described in detail.
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Scientific studies of Aloe vera have tentatively explained therapeutic claims from a mechanistic perspective. Furthermore, in vitro outcomes demonstrate that the breakage of acemannan chains into smaller fragments enhances biological effects. These fragments can intravenously boost vaccine efficacy or entrain the immune system to attack cancer cells by mannose receptor agonism of macrophage or dendritic cells. With oral consumption, epithelialisation also occurs at injured sites in the small intestine or colon. The main advantage of dietary acemannan is the attenuation of the digestive process, increasing satiety, and slowing the release of sugars from starches. In the colon, acemannan is digested by microbes into short-chain fatty acids that are absorbed and augment the sensation of satiety and confer a host of other health benefits. In topical applications, an acemannan/chitosan combination accelerates the closure of wounds by promoting granular tissue formation, which creates a barrier between macrophages or neutrophils and the wound dressing. This causes M2 polarisation, reversal of inflammation, and acceleration of the re-epithelialisation process. This review summarises and explains the current pharmacodynamic paradigm in the context of acemannan in topical, oral, and intravenous applications. However, due to contradictory results in the literature, further research is required to provide scientific evidence to confirm or nullify these claims.
Conference Paper
The burden (economic and medicinal) of acute and chronic gut disorders continues to increase. As efficient therapies are few, attention has turned towards the use of so-called functional foods to mediate against gut disorder. These target particular genera of gut bacteria seen as beneficial, e.g. bifidobacteria, lactobacilli. The use of products containing live microbial species (probiotics) has a long history of use in humans and many trials have been reported as 'positive'. Taking the view that positive components of the gut flora already exist in the intestinal tract, the prebiotic concept has been developed. Here, dietary carbohydrates have a selective metabolism within the gut flora thereby shifting the community towards a more advantageous structure. Conventional fibres like pectins, cellulose, etc. are not selectively metabolised by gut bacteria. However, certain oligosaccharides do have this capability. Most research has been conducted with fructooligosaccharides, like inulin, which have a powerful bifidogenic effect. Trials are ongoing to determine the clinical benefits of prebiotic use. Intestinal disorders like ulcerative colitis, gastroenteritis and irritable bowel syndrome are particular targets. (c) 2004 Elsevier Ltd. All rights reserved.
INTRODUCTION Gut microbial communities have existed since the earliest multicellular life forms developed a digestive tract. In invertebrates and vertebrates that rely largely on plant material as their main source of energy, the gut microbial community plays a crucial nutritional role in supplying energy to the host through anaerobic fermentation of plant structural polysaccharides. This type of symbiotic association has been studied particularly in ruminants, where the host derives around 75% of its energy from the diet via microbial fermentation (Hungate, 1966), and in the termite gut (Brune, 1998). In all hosts, however, including carnivores and omnivores, where their nutritional contribution is less important, the gut microbiota exert a major influence on health as a potential source of infectious agents, as a barrier against infectious agents and as determinants of the gut environment, gut metabolism and immune development. This chapter will consider the extent and significance of microbial diversity in gut communities, with particular reference to the microbiota of the human large intestine. The best-studied gut inhabitants are of course pathogens such as Escherichia coli, but there is increasing awareness of the importance of the numerically predominant commensal colonizers of the gastrointestinal tract. MICROBIAL DIVERSITY IN THE HUMAN LARGE INTESTINE Diversity revealed by 16S rRNA gene sequences The communities of the human large intestine and rumen show the highest prokaryote cell density of any microbial ecosystem, approaching or exceeding 1011 cells g−1 (Whitman et al., 1998). © Society for General Microbiology 2006, except for the chapters by UK and US Government employees.
Phenotypic and phylogenetic studies were performed on two isolates of an unidentified Gram-positive, anaerobic, non-spore-forming, rod-shaped bacterium that was isolated from human faeces. The organisms were catalase-negative, produced acetic and butyric acids as end products of metabolism and possessed a DNA G+C content of approximately 54 mol%. Comparative 16S rRNA gene sequencing demonstrated that the two isolates were related closely to each other and formed a hitherto unknown sublineage within the Clostridium leptum rRNA cluster of organisms. Based on phylogenetic and phenotypic evidence, it is proposed that the unknown bacterium should be classified in a novel genus as Anaerotruncus colihominis gen. nov., so. nov. The type strain of Anaerotruncus colihominis is WAL 14565(T) = CCUG 45055(T) = CIP 107754(T).
A study was made of the effects of fructooligosaccharides, which exist widely inplants such as onion, edible burdock, wheat etc., on the human and animal intestinal flora. Fructooligosaccharides are produced from sucrose with the aid of β-fructofuranosidase from Aspergillus niger on a commercial scale by Meiji Seika Kaisha, Ltd.(Neosugar, Meioligo®). It has been found that they are not hydrolyzed by any digestive enzymes of humans and animals. Moreover utilization byvarious kinds ofintestinal bacteria indicated that Bifidobacterium spp., the Bacteroides fragilis group, Peptostreptococcus spp. and Klebsiella pneumoniae can utilize these saccharides, but Clostridium perfringens, Escherichia coli and others cannot. The fructooligosaccharides are selectively utilized, particularly by bifidobacteria.The clinical studies showed that fructooligosaccharides administration improved the intestinal flora, with subsequent relief of constipation, improved blood lipids in hyperlipidemia, and suppressed the production of intestinal putrefactivesubstances.
In recent years there have been some startling advances made in the taxonomy of bifidobacteria. The bifidobacteria are classified as a distinct genus Bifidobacterium, and a number of species and biovars are now recognized. As better techniques for the study of bacteria are devised, more definitive information on importance of bifidobacteria as part of the intestinal flora of humans and animals has been obtained. Some ecological relationships of this organism are reviewed in this paper.