Polysaccharides
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• Introduction of polysaccharides
• Polysaccharide sources and characterization
• Polysaccharide structure analysis
• Functions of polysaccharides
• Selecting polysaccharides for food applications
Polysaccharides: Introduction
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Definitions of polysaccharides
• “Polysaccharide” is the name given to a macromolecule consisting of a
large number of monosaccharide residues joined to each other by
glycosidic linkages.
• Polysaccharides composed of only one kind of monosaccharide are
described as homopolysaccharides (homoglycans). Similarly, if two or
more different kinds of monomeric unit are present, the class name
heteropolysaccharide (heteroglycans) may be used.
• A general term for a homopolysaccharide is obtained by replacing the
ending “-ose” of the sugar name by “-an”. For example: xylan for
polymers of xylose, mannan for polymers of mannose, and galactan for
polymers of galactose. Cellulose and starch are both glucans, as they
are composed of glucose residues
Adapted from IUPAC Nomenclature of Carbohydrates (1996) http://www.chem.qmul.ac.uk/iupac/2carb/
Polysaccharides: Introduction
3
Shorthand Notation
 Glycosyl units are represented by the first 3 letters of their names, except
for glucose which is Glc
 Sometimes D is omitted; if it is an L sugar, the L is put in the designation
 Ring size: p or f
 Uronic acids are indicated by a suffix A
  and  are designated where appropriate
 Examples
 Cellobiose = -Glcp(14)-Glc or Glcp1,4Glc
 Lactose = -Galp(14)-Glc or Galp1,4Glc
 Maltose = -Glcp(14)-Glc or Glcp1,4Glc
 Gellan = [3)--D-Glcp-(14)--D-GlcpA-(14)--D-Glcp-(14)--LRhap-(1 ]n
Polysaccharides: Introduction
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Classification of Polysaccharides
Polysaccharides by source
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Seaweed extracts: Agars, alginates, carrageenans
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Higher plant cell walls insoluble: cellulose
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Higher plant cell wall soluble: pectin
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Higher plant seeds: cereal starch, guar gum, locust bean gum
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Higher plant tuber & root: potato starch, tapioca starch
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Higher plant exudates: gum arabic, gum tragacanth
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Microorganism: Xanthan gum, Gellan gum
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Derived: modified starch, carboxymethyl cellulose, propylene glycol
alginate
Polysaccharides: Introduction
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Classification of Polysaccharides
Polysaccharides by structure
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Linear: amylose, cellulose, pectin, alginates
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Short branched: guar gum, locust bean gum, Xanthan gum
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Branch-on-branch: amylopectin, gum arabic, arabinoxylan
Polysaccharides by monomers
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Homoglycans: starch, cellulose
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Diheteroglycans: agars, alginate, carrageenans,
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Triheteroglycans: Xanthan, Gellan, arabinoxylan
Polysaccharides by charge
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Neutral: amylose, amylopectin, cellulose, guar gum
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Anionic: alginates, pectin, carrageenans, Gellan, gum arabic, Xanthan
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Cationic: chitosan
Polysaccharides: Introduction
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Molecular weight and degree of polymerization
 Molecular weight (MW):
 The mass of one molecule of the substance, relative to the
“unified atomic mass unit” (equal to 1/12 the mass of one atom
of carbon-12)
 Degree of polymerization (DP):
 The number of monomeric residues in a polymer molecule
 “Chain length”, expressed in DP, is used to quantify the size
of polysaccharide chains
Polysaccharides: Introduction
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Polydisperse and polydispersity
GGGGGGGGG
GGGGG
This collection of molecules is polydisperse
GGGGGGGGGGGGG
Polydispersity index (PDI):
 Ratio of the weight average molecular weight to the number average
molecular weight
 Indicating the overall distribution of individual molecular weight in a
batch of polymers
 PDI equal to 1 indicates only one length of polymer is present
 In polysaccharides (e.g. starch), PDI may vary significantly.
Polysaccharides: Introduction
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Number average molecular weight (MN)
 MN = iNiMi/iNi , where Ni is the number of molecules of
molecular weight Mi
 Can be determined by osmometry, end group titration,
and colligative properties
 MN is more weighted by the small molecules in the
molecular population
Polysaccharides: Introduction
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Weight average molecular weight (MW)

MW = iNi(Mi)2/iNiMi, where Ni is the number of molecules
of molecular weight Mi

Can be determined by light scattering, small angle neutron
scattering (SANS), X-ray scattering, and sedimentation
velocity

MW is more weighted by the large molecules
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Polysaccharides: Introduction
Polydispersity index = MW/MN
Polysaccharides: Introduction
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An example of MW,MN, and polydispersity index
Mi (DP)
Ni
NiMi
Ni(Mi)2
100
10
1,000
100,000
10
10
100
1,000

20
1,100
101,000
MW = iNi(Mi)2/iNiMi
MN = iNiMi/iNi
101,000/1100 = 91.8 (DP)
1,100/20 = 55 (DP)
So, polydispersity index = 91.8/55 = 1.67
Polysaccharides: Introduction
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Chain length distribution of starch: HPSEC & FACE
High performance size-exclusion chromatography
Fluorophore-assisted carbohydrate electrophoresis
Polysaccharides: Introduction
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A case study: eel feed &
polysaccharides
Eel feed
http://fishology.bl
ogspot.com/2012/
08/eel.html
Eel food
http://www.japantimes.co.jp/life/2013/07/13/travel/hot-weathers-cold-comfort-for-eels/
Polysaccharides: Introduction
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Eel eats fish or fish meal
Major components of eel feed dough:
• Fish meal: white fish meal or red fish meal, ~70%
• Pre-gelatinized potato starch or/and tapioca starch, as
binder, ~25%
• Nutrients (minerals, yeast, etc.) and others, ~5%
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Polysaccharides: Introduction
Eel feed: big dough shared by hundreds of eels
• All ingredients are blended and added with water. After
kneading, a big dough forms
• The dough is thrown in water; eels race to the dough and
bite
• The dough needs to be cohesive enough to stay in large pieces
Eels are very picky with their foods: they do not
like a dough that is not elastic enough
Polysaccharides: Introduction
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We want to cut the cost of eel feed
• Usually white fish meal (~$600/MT) is used for eel feed.
The project was to replace white fish meal using red fish
meal (~$400/MT)
• However, red fish meal contains much higher lipid (fatty
acids) amount than white fish meal. The dough with red
fish meal has low elasticity and may easily dissemble in
water
• And eels don’t want to eat it…
Polysaccharides: Introduction
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The reason:
•
In red fish meal, lipid is hydrolyzed by
lipase, and fatty acids are released at a
much higher amount
•
Fatty acids form starch-lipid complex with
amylose of starch
•
Gel structure of dough is damaged by
starch-lipid complex, and the
viscoelasticity is partially lost
We either had to remove lipid from fish meal,
or enhance the gel strength of potato starch by
adding additional binders
So, our strategy was to…
Buleon et al., Int. J. Biol.
Macromol. (1998) 23, 85
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Polysaccharides: Introduction
To add non-starch polysaccharides (food gums)
as binders to the dough system, in order to
improve gel strength, cohesiveness, and elasticity
Polysaccharides: Introduction
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To increase the viscosity, we tested:
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Carboxymethyl cellulose (CMC)
Guar gum
Locust bean gum
Alginate, agar, carrageenans
Pectin
Xanthan gum
Konjac flour
Gum arabic
To increase the gel strength, we tested:
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Locust bean gum + Xanthan gum
Locust bean gum + carrageenans
Modified starches
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Polysaccharides: Introduction
We found, with up to 1% level:
• Some gums improved the cohesiveness (less sticky
dough) and retain water better, but the dough was
not elastic
• Some gums had no observable effects
• Some gums reduced the gel formation of potato
starch, and resulted in reduced cohesiveness and
elasticity
• Gelling agents basically had no effect on the
overall gel strength or elasticity of dough
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Polysaccharides: Introduction
Some fundamental questions are:
• What are the interactions among polysaccharides,
lipids, and protein?
• What are the interactions among starch and non-starch
polysaccharides?
• What are the interactions between two gel networks,
e.g. starch gel network & LBG-Xanthan gel network?
• How do polysaccharide-lipid-protein interactions affect
the physical properties of dough?
Polysaccharides: Introduction
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We also tested other approaches, e.g. converting fatty
acids to substances with reduced impact on starch gel
structure. However, the “red fish meal for eel feed” still
seems to be a good challenge
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Polysaccharides: sources and characterization
Polysaccharides from seed, tuber, or root: Starch
• A most abundant carbohydrate
• Major component of human diet
Amylose
• Various digestibility
• Numerous applications as ingredients
• Comprising linear molecules, amylose,
& branched molecules, amylopectin
• Subjected to genetic, chemical, physical,
and enzymatic modifications
Amylopectin
• Subjected to acidic and enzyme
hydrolysis to maltodextrins and syrups
• Basic ingredient of many food and nonfood industries
Adopted from: http://www.oci.unizh.ch/edu/lectures/material/AC_BII/Kap14/kap14.html
Polysaccharides: sources and characterization
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Polysaccharides from seed: Guar gum
http://en.wikipedia.o
rg/wiki/Guar_gum
http://guargum-sd.com/
http://www.guarglobal.com/oppo
rtunity/guar-global-markets
• Galactomannan obtained from the seed of guar plant, Cyanaposis tetragonolobus, mostly
in India and Pakistan
• Chains of (14)-linked -D-mannopyranosyl units, with averagely 1.8 chain units
attached with single -D-galactopyranosyl units via (16)-linkages
• Distribution of side units is relatively even along the main chain
• Neutral polysaccharide with molecular weight: 150,000 – 1,500,000
• Soluble in cold water
• Showing pseudoplastic (shear thinning) behavior in solution
• Does NOT form gel with xanthan gum
• US $2,000-10,000/Ton (Corn starch: US $550-650/T)
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Polysaccharides: sources and characterization
Polysaccharides from seed: Guar gum
http://www.guarglobal.com/opportunit
y/guar-economics
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http://en.wikipedia.org/wiki/Hydraulic_fracturing
Shale oil and gas extraction industries consume the majority of guar gum for Hydraulic fracturing (fracturing of rock
by a pressurized liquid, fracking)
Fracking is conducted once in the life of the well and greatly enhances well productivity
In the past 60 years, 2.5 million hydraulic fracturing jobs have been performed on oil and gas wells worldwide, more
than one million of them in the US
Fracture fluid contains water-soluble gelling agents (e.g. guar gum) to increase viscosity and effectively deliver the
proppant (sands, ceramics, etc.)
Conventional linear gels are used: e.g. CMC, guar and its derivatives
Borate-crosslinked: guar-based fluids cross-linked with boron ions, to provide high viscosity at pH 9 to carry
proppants. After the fracturing the pH is reduced to break the gel
Organometallic-crosslinked fluids: also to crosslink guar gum
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Polysaccharides: sources and characterization
Polysaccharides from seed: Locust bean gum
http://www.jpbsonline.org/viewimage.asp?img=JPh
armBioallSci_2012_4_3_175_99013_u2.jpg
http://www.gumtech.com/products/ProductInfo
.php?product=Locust%20Bean%20Gum
• Galactomannan obtained from the seed of carob tree, Ceratonia
siliqua, around the Mediterranean Sea
• Chains of (14)-linked -D-mannopyranosyl units, with
averagely 3.9 chain units attached with single -Dgalactopyranosyl units via (16)-linkages
• Distribution of side units is highly uneven along the main chain
• Neutral polysaccharide with molecular weight: 400,000 1,000,000
• Requires heating to hydrate completely
• Showing pseudoplastic behavior in solution
• Forms gel with xanthan gum
• US $25-30 / Kg (seed $7000/T)
http://vasugum.com/locust-bean-gum/
Polysaccharides: sources and characterization
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Polysaccharides from seed: Tara gum
• Galactomannan obtained from the seed of Tara shrub, Caesalpinia spinosa, mostly in
northern Africa and South America (Peru)
• Main chain of (14)-linked -D-mannopyranosyl units, with single -D-galactopyranosyl
units attached with average 3 main chain units via (16)-linkages
• Molecular weight may fall between 300,000 to 1,000,000
• 70% soluble in cold water and 100% hydrated at >80C
• Showing pseudoplastic behavior in solution
• Difficult to form gel with xanthan gum
• US $8.00-9.00/kg
http://en.silvateam.com/Products-Services/Food-Ingredients/Tara-gum/Production-process
Polysaccharides: sources and characterization
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Polysaccharides from tuber: Konjac flour
• Glucomannan obtained from the tuber of Amorphophallus konjac grown in Asia
• Chain of mannose and glucose units in a molar ratio of 1.6:1 connected with -(14)linkages. One acetyl group presents at the C-6 for about 6 to 20 sugar units
• Neutral polysaccharide with molecular weight: 200,000 - 2,000,000
• Swells in cold water, fully hydrates after heating
• Showing pseudoplastic behavior in solution
• US $5.30-5.50/kg
http://www.ricepl
ex.com/KonjacRootGlucomannanPowder.html
http://www.glucomannan.com/
http://en.wikipedia.org/wiki/Konjac