Polysaccharides
Biopolymers (polyhydroxyalkanoates)
POLYSACCHARIDES
Microbial polysaccharides are used for food, pharmaceutical,
and medical applications: this wide range of usefulness derives
from the great diversity in structural and functional
properties.
Applications
of
commercially
available
microbial
polysaccharides including xanthan, xylinan, gellan, curdlan,
pullulan,
dextran,
scleroglucan,
schizophyllan,
and
cyanobacterial polysaccharides
The commercial value of polysaccharides is based on its ability
to modify the flow characteristics of solutions (Rheology).
They can incr viscosity and hence used as thickening and gelling
agents.
•
Polysaccharides made by microrganisms are secreted from the cell to form a
layer over the surface of the organism, often of substantial depth in
comparison with the cell dimensions (Figure 1).
Because of their position they are characterized as exopolysaccharides, to
distinguish them from any polysaccharides that might be found within the cell.
The functions are thought to be mainly protective, either as a general physical
barrier preventing access of harmful substances, or more specific as a way of
binding and neutralizing bacteriophage. In appropriate environments they may
prevent dehydration.
Exocellular or ‘capsular’ polysaccharide layer
(labeled P) from Streptococcus pneumoniae
•
Prevent phagocytosis by other micro- organisms or the cells of the immune system.
The capsular polysaccharides (CPSs) are often highly immunogenic, and may have
evolved their unusual diversity as a way of avoiding antibody responses: advantage of
this feature can be taken in the development of vaccines.
•
adhesion and penetration of the host; Plant lectins (glycoproteins) that have specific
binding properties with respect to carbohydrate structures; general defense of
plants against bacterial infection.
•
Polysaccharides can be involved in pathogenicity. Pseudomonas aeruginosa, commonly
found in respiratory tract infections, produces alginate which contributes to blockage
in the respiratory tract
• polysaccharide biotechnology: xanthan, priced at about US$14 per kg, used
mainly in food applications, to cyclic dextrans, valued at about US$50perkg
and used in high-value applications in research and pharmaceuticals
• Certain microbes are known to produce nearly all the major plant
polysaccharides such as glucans, alginate-like materials, and even cellulose –
as well as the complex bacteria-specific materials.
Production
Batch culture
Excess of carbon supply
Carbon/nitrogen ratio of 10:1
When acidic PS limited polysaccharides are synthesized
90% oxygen saturation
Biosynthesis
Starting with glucose or appropriate sugar and several enzymatic
reactions,
Recovery
Marked increase in viscosity of culture broth
Can be precipitated by salts, acids or organic solvents
Microbial PS
20 PS of commercial adv and value
Dependent of rheological property
Only microbial polysaccharide currently
produced on a Large scale: XANTHAN
Plant PS
Cheap
Uncontrolled
Occurs for a short duration
Production: 20,000 tonnes per year
E415
XANTHAN: polysaccharide polymer produced by Xanthomonas campestris
Long chain polysaccharide composed of the sugars glucose, mannose, and glucuronic acid. The
backbone is similar to cellulose, with added sidechains of trisaccharides (3 sugars in a chain)
Gram negative bacteria, plant pathogen causes black rot in Brassica (cauliflower and
broccoli) produces a slimy gel that protects bacteria from viruses and prevents it from
drying out.
Has very high viscosity and is stable at extreme physical and chemical
environments, shows physical and chemical properties like plastic, used in many
ways: eg. oil drilling
Pentasaccharide: Glu-man-glcA-Ac-Pyr
Branched polymer with b-1,4 linked glucan (glucose polymer)
backbone bound to trisaccharide (Man, GlcA, Man). Man has Acetate
or Pyruvate groups (number is variable dependent on bacterial strain)
Viscosity is denpendent on contents of pyruvate and acetate
Glucan backbone
B-glc (1-4)-B-Glc (1-4)
1-3
Pyr
4
6
b-Man-(1,4)-b-GlcA- (1-2)-a-Man-6-O-Ac
Trisaccharide chain
Commercial production of Xanthan Gum
X. Campestris should be grown on a cheap and abundant source of carbon
Wild type can use glucose, sucrose and starch but not lactose
Whey is a waste product of cheese making industry used as filler in several foods
95% water, 3.5-4% lactose and small amounts of proteins, minerals LMW organic cpds
Only advantage is that it can be used as a carbon source for growing industrial MO
Due to lactose intolerance alternatives are required
Disposal of whey in rivers can lead to depletion of dissolved O2
Transporation of whey to landfill sites is exceptionally expensive
Groundwater leaching and contamination a concern
Genetic engineering of X. campestris to grow on WHEY
E.coli lacZY (b-galactosidase and lac permease)cloned to broad host range
plasmid under transcriptional control of X. campestris bacteriphase promoter.
Introduced in E.coli and transformed to X. campestris by tripartite mating
Transformants wgich maintained the plasmid expresses lacZY and used lactose
as sole carbon, produced hih levels of xanthan gum with glucose, lactose or
whey as carbon source.
Compared to wild type which produced xanthan only when grown on glucose
Helped to convert a nuisance waste product into a substrate for production of
economically valuable bopolymer.
DEXTRANS
They are glucans (polymers of glucose)
A(1-6) linkages some have a-1,2 and a1,3, and 1,4
MW is 15,000-500,000
Applications: Blood plasma expanders for prevention of thrombosis
Wound healing and dressing
purification of biomolecules
Production
Microorganisms like Leuconostoc mesentroides
They are produced by extracellular enzymes like
dextransucrase which act on sucrose and bring
polymerization of glucose residues and liberates free
fructose in medium
Batch fermentation
Multi-celled Algae (divided into several groups across
classification)
␣ Have a similar function as plants do on land
␣ Photosynthesize, base of food chain, provide habitat for
other organisms
␣ Most live attached to rocks
␣ Structures are different from plants
Division (Phylum) Chlorophyta Green algae
Division (Phylum) Rhodophyta Red Algae
Division (Phylum) Phaeophyta Brown algae
Algae Structures
Photosynthesis, takes up water and
nutrients
Buoyancy: air filled, allows algae to
float in water
Photosynthesis, takes up water and
nutrients
Attaches algae to rock, doesn’t
grow into rock, only for attachment
Seaweed and marine algae
have been valued for centuries in Asia and
the Pacific Islands for their nutritional and healing properties as they are packed
with potassium, vitamins A, B, C, D, and E.
They are very high in iodine content and are used to treat some thyroid conditions.
A brown seaweed (kelp), is found to have antibacterial and antiviral properties and
has been extensively used in clinical trials to lower blood pressure in heart patients.
Several marine seaweeds and submerged vegetation in seawater are
reported to have antagonistic activity and have been found effective
against various viruses.
Polysaccacharides from marine environment
Purple layer contains a sulphated polysaccharide called Porphyran, which is
a complex galactan, and has shown higher gelling capacity reported to
inhibit the growth of Sarcoma 180 tumors in mice.
A substance named porphyosin isolated from Porphyra exhibited anti ulcer
activity.
4-linked 6-O-sulfo-α-L-galactopyranose residue
(the biological precursor of the 3,6-anhydro
residue (agarose)
3-linked 6-O-methyl-β-Dgalactopyranose residue
red alga Porphyra umbilicalis
Agar: well known gelling agent. Gelidium spp. Gracilaria (Red seaweeds (Rhodophyceae)
Agarose
Agaropectin
RED ALGAE
(1 4)-3,6-anhydro-α-L-galactopyranosyl-(1 3)-β-D-galactopyranan
Agarose is purified form of agar. Both have variety of uses in
biochemistry, molecular biology, microbiology.
Used as gelling agent for meats, confectionery, icing stabilizer in baked
goods in food industry
Used as laxative (as it cannot be metabolized) in medicinal applications
Also as flexible moulds in dentistry and criminology
Agar polysaccharides are effective against poliovirus, herpes simplex, dengue viruses, etc.
Alginates soluble in water and form gels with addition of calcium or bivalent ions
Calcium ions form a link b/w G molecules
If ions removed gel will break
Alginate
gels
cannot
be
reversed and are not stable at
low pH.
But
high
viscosity
and
hydration make them useful for
salad dressings, frozen foods,
icings and film formation.
Textile and paper industry uses
to thicken inks, coat papers and
reduce staining
Enzyme immobilization
Phaeophyceae
BROWN ALGAE
Laminiaria spp.
Sargassam spp.
Calcium alginates provide a moist healing
environment by converting the exudate into a
gel.
A reaction between the calcium in the
dressing and the sodium in the wound exudate
results in a chemical ion exchange, which
forms a gel-like substance.
The gel conforms to the wound, providing a
soft, moist healing environment. Due to it’s
dehydrating effect, this dressing should not
be used with dry wounds.
Also shows hemostatic activity
Sorbsan is made from seaweed
into delicate fibers and cut into
unwoven sheets
Sorbsan can be easily
separated and fluffed up
before placing it into a wound
bed
30000 tonnes per year and supply much more than this
Carrageenans
First in Ireland
Carrageenans are ideal food additives:
they have a range of gelling and
emulsifying properties ranging from a
soft slime to a brittle gel that one could
nearly walk upon.
Rhodophyceae
RED ALGAE
They also have a high reactivity with a
range of materials including, most
importantly, milk proteins, being widely
used at low concentrations in dairy
products to prevent fractionation of
milk constituents.
In fact, a major application is found in
chocolate milk, a very popular daily drink
in the USA and Europe, and now
spreading elsewhere.
Carrageenans are also very good at
keeping chocolate in suspension.
Best quality from Philippines
SCLEROGLUCAN
GLUCOSE POLYMER (glucomer)
Neutral polysaccharide with b-1,3 glucan backbone and single
glucose residue branches b (1,6)
Branching occurs at a regular sequence at every 3rd glucose unit
in the polymer backbone chain
Scleroglucan is a fungal hexopolysaccharide
Useful for stabilizing latex paints, printing inks and drilling muds
GELLAN
Linear heteopolysaccharide
2glu, 1GlcA and one rhamnose
Pseudomonas elodea
A deacetylated gellan forms fim brittle gels : GELRITE (US company)
Used in food industry as low temperature thickner
POLLULAN
A GLUCOSE POLYMER (a-glucan) with a-1,4 and few a 1,6
70% of glucose is converted to pollulan
Fungus: Aurobasidium pollulans
CURDLAN
A GLUCOSE POLYMER (b-glucan) glucose hed by b-1,3
Alcaligenes faecalis, Rhizoium trifolli, Agarobacterium rhizogenes
Forms strong gels ehen heated to 55oC, gelling agent, immuno
modulator and immobilization of enzymes
Pectin
α-(1-4)-linked Dgalacturonic acid
Pectin is a long chain of pectic acid
and pectinic acid molecules. Because
these acids are sugars, pectin is a
polysaccharide. It is prepared from
citrus peels and the remains of
apples (pomace) after they are
squeezed for juice.
In the plant, pectin is the material that joins the
plant cells together. When fungus enzymes break
down the pectin in fruit, the fruit gets soft and
mushy.
During ripening, pectin is broken down by the enzymes pectinase and
pectinesterase; in this process the fruit becomes softer as the cell walls
break down.
Uses
•Pectin is a thickener in many products. If there is sufficient sugar in the
mixture, pectin forms a firm gel.
•Jams and jellies are thickened with pectin. Pectin binds water, and thus keeps
products from drying out. It stabilizes emulsions.
•Pectin combines with the calcium and whey proteins of milk, stabilizing foams
and gels made with cream or milk.
•In the cigar industry, pectin is considered an excellent substitute for
vegetable glue and many cigar smokers and collectors will use pectin for
repairing damaged tobacco wrapper leaves on their cigars.
•Pectin is also used in throat lozenges as a demulcent. In cosmetic products,
pectin acts as stabilizer. Pectin is also used in wound healing preparations and
specialty medical adhesives, such as colostomy devices
•Pectin is not digested, and is considered a beneficial dietary fiber.
In human digestion, pectin passes through the small intestine more or less intact. In the large
intestine and colon, microorganisms degrade pectin and liberate short-chain fatty acids that
have positive influence on health (prebiotic effect)
Ghum or Gum Materials
Natural gums are polysaccharides of natural origin, capable of causing a
large viscosity increase in solution, even at small concentrations. In the
food industry they are used as thickening agents, gelling agents,
emulsifiers and stabilisers.
1.
2.
3.
4.
5.
E numbers are number codes for food
additives and are usually found on food
labels throughout the European Union
Agar (E406), obtained from seaweed
Alginic acid (E400), from seaweed
Beta-glucan, from oat or barley bran
Carrageenan (E407), from seaweed
Chicle gum, an older base for chewing gum
obtained from the chicle tree
6. Dammar gum, from the sap of Dipterocarpaceae
trees
7. Gellan gum (E418), produced by bacterial
fermentation
8. Glucomannan (E425), from the konjac plant
9. Guar gum (E412), from guar beans
10. Gum arabic (E414), from the sap of Acacia trees
11. Gum ghatti, from the sap of Anogeissus trees
12. Gum tragacanth (E413), from the sap of
Astragalus shrubs
13. Karaya gum (E416), from the sap of Sterculia
trees
14. Locust bean gum (E410), from the seeds of the
carob tree
15. Mastic gum, a chewing gum from ancient Greece
obtained from the mastic tree
16. Psyllium seed husks, from the Plantago plant
17. Sodium alginate (E401), from seaweed
18. Spruce gum, a chewing gum of American Indians
obtained from spruce trees
19. Tara gum (E417), from the seeds of the tara
tree
20. Xanthan gum (E415), produced by bacterial
fermentation
Beta-glucan, from oat or barley bran
polysaccharides occurring in the bran of cereal grains, the cell wall of baker's
yeast, certain types of fungi, and many kinds of mushrooms.
The cereal based beta-glucans occur most abundantly in barley and oats and to a
much lesser degree in rye and wheat.
They are useful in human nutrition as texturing agents and as soluble fiber
supplements, but problematic in brewing as excessive levels make the wort too
viscous.
Yeast derived beta glucans are notable for their immunomodulatory function.
The differences between soluble and insoluble beta glucans are significant in
regards to application, mode of action, and overall biological activity.
Beta 1,3-D glucans are being referred to as biological response modifiers
because of their ability to activate the immune system.
However, it should be noted that the activity of Beta 1, 3-D glucan is
different from agents that stimulate the immune system.
Agents that stimulate the immune system can push the system to overstimulation, and hence are contraindicated in individuals with autoimmune
diseases, allergies, or yeast infections.
Beta 1, 3-D glucans seem to make the immune system work better
without becoming overactive. They accomplish this by activating
phagocytes, which are immune system cells whose function is to trap and
destroy foreign substances in our bodies such as bacteria, viruses, fungi,
and parasites.
In addition to enhancing the activity of phagocytes, beta-1,3 glucans
also reportedly lower elevated levels of LDL cholesterol, aid in wound
healing, help prevent infections, enhance NK cell function, and help in
the prevention and treatment of cancer
Chicle gum is the natural gum from Manilkara chicle,
Wrigley Company was a prominent user of this material, today there are only a
few companies that still make chewing gum from natural chicle. This is because
by the 1960s chicle was replaced by butadiene-based synthetic rubber which
was cheaper to manufacture.
Gellan gum: is a water-soluble polysaccharide produced by Sphingomonas elodea
Also known commercially as Phytagel™ or Gelrite®, is used primarily as a
gelling agent, alternative to agar, in microbiological culture.
It is able to withstand 120 °C heat, making it especially useful in culturing
thermophilic organisms.
One needs only approximately half the amount of gellan gum as agar to
reach an equivalent gel strength, though the exact texture and quality
depends on the concentration of divalent cations present
Dammar Gum or Jhuna used as room freshner,
control of mosquitoes and in worshiping
Glucomannan is mainly a straight-chain polymer, with a small amount of branching.
The component sugars are β-(1→4)-linked D-mannose and D-glucose in a ratio of
1.6:1.
The degree of branching is about 8% through β-(1→6)-glucosyl linkages.
Konjac
Guar gum, also called guaran, is a
galactomannan. It is primarily the
ground endosperm of guar beans.
The guar seeds are dehusked, milled
and screened to obtain the guar
gum.
It is typically produced as a free
flowing, pale, off-white colored,
coarse to fine ground powder.
Guar gum retards ice crystal growth
non-specifically by slowing mass
transfer across the solid/liquid
interface. It shows good stability
during freeze-thaw cycles
Psyllium seed husks,
plantago
Isabgol
Animal Biomass: Chitin
b-1,4
linkage
N-acetylglucosamine
Chitin is a long-chain polymer of a N-acetylglucosamine, a derivative of
glucose.
It is the main component of the cell walls of fungi, the exoskeletons of
arthropods, such as crustaceans (like the crab, lobster and shrimp) and the
insects, including ants, beetles and butterflies, the radula of mollusks
and the beaks of the cephalopods, including squid and octopuses.
Chitin has also proven useful for several medical and industrial purposes.
Chitin is a biological substance which may be compared to the
polysaccharide cellulose and to the protein keratin. Although keratin is a
protein, and not a carbohydrate like chitin, both keratin and chitin have
similar structural functions.
Chitin is the second most abundant polysaccharide in nature (after
cellulose). At least 10 gigatons of chitin are synthesized and degraded each
year in the biosphere.
Chitin is translucent, pliable, resilient and quite
tough.
In arthropods, however, it is often modified,
becoming embedded in a hardened proteinaceous
matrix, which forms much of the exoskeleton.
In its pure form it is leathery, but when encrusted
in calcium carbonate it becomes much harder
Chitin is one of many naturally occurring polymers.
Its breakdown may be catalyzed by enzymes called chitinases,
secreted by microorganisms such as bacteria and fungi, and
produced by some plants.
Some of these microorganisms have receptors to simple sugars
from the decomposition of chitin.
If chitin is detected, they then produce enzymes to digest it by
cleaving the glycosidic bonds in order to convert it to simple
sugars and ammonia.
Chitosan (a more water-soluble derivative of chitin).
It is also closely related to cellulose in that it is a long
unbranched chain of glucose derivatives.
Commercially derived from shrimps
Preparation of
chitin and chitosan
Biotechnological Uses of Chitinolytic enzymes
Chitin has a broad range of applications in biochemical, food, and various
chemical industries.
It has antimicrobial, anticholesterol and antitumor activities
Chitin and its related materials are also used in wastewater treatment
drug, wound healing, and dietary fiber
Industrial (water purification, stabilizer, pharmaceuticals)
Medicinal (surgical threads, wound healing, role in immune response to
allergic diseases)
Agricultural (inducer of plant immune system and hence enhance defense
mech.; fertilizer
Chitinases
In vertebrates, chitinases are usually part of the digestive tract.
In insects and crustaceans, chitinases are associated with the need
for partial degradation of old cuticle.
Implicated in plant resistance against fungal pathogens because of
their inducible nature and antifungal activities invitro (Chitinase in
fungi is thought to have autolytic, nutritional, and morphogenetic
roles.
In viruses, chitinases are involved in pathogenesis
In bacteria, chitinases play a role in nutrition and parasitism.
In addition to the above potential applications,
chitinases can be used for the production of chitooligosaccharides,
which have been found to function as antibacterial agents, elicitors
of lysozyme inducers, and immunoenhancers
Chitinases can also be used in agriculture to control plant pathogens