Carbohydrates

Introduction to Carbohydrates
• Carbohydrates are sugars and provide
energy when consumed.
• Our bodies break down carbohydrates to
extract energy. Carbon dioxide and water are
released in the process.
• Glucose is the primary carbohydrate our
bodies use to produce energy.

• Composed of the elements C, H and O
• Produced by photosynthesis in plants

• Carbohydrates contain the elements:
Carbon
Hydrogen
Oxygen
• The formula for a carbohydrate is
(CH2O)n
• The n represents the number of times
the CH2O unit is repeated.

• Simple carbohydrates are referred to as
simple sugars and are often sweet to the
taste.
• Complex carbohydrates include starches
and the plant and wood fibers known as
cellulose.
• Consumption of more sugar than is
needed for energy results in conversion of
these sugars to fat.

• Monosaccharides are the simplest
carbohydrates. They cannot be broken down to
smaller carbohydrates.
• Disaccharides consist of two monosaccharide
units joined together; they can be split into two
monosaccharides.
• Sucrose, table sugar, can be broken down into
glucose and fructose.
• Oligosaccharides
• contain anywhere from three to nine
monosaccharide units.
Classification of Carbohydrates

• Polysaccharides are large molecules
containing 10 or more monosaccharide units.
• Carbohydrate units are connected in one
continuous chain or the chain can be
branched.
• a) Homosaccharides.
• b) Heterosaccharides.
• c) Derived carbohydrates.

Physical Characters
• Condition:
Sugars are white, crystalline in shape and with sharp
melting points, while polysaccharides are white
amorphous solids.
• Taste:
- Sugars have a sweet taste.
- Polysaccharides are tasteless.
• Solubility:
-Monosaccharides are soluble in cold water and hot
alcohol.
- Polysaccharides are partially soluble in hot water.

• simple sugars.
• consist of one sugar unit.
• Non-hydrolysable.
• Classification:
• a) according to the number of C- atoms
– Triose contains three carbons, i.e glyceraldehyde.
– Tetrose contains four carbons, i.e erythrose.
– Pentose contains five carbons.
– Hexose contains six carbons
Monosaccharides

• b) according to the type of the carbonyl
group (C=O)
- Aldoses: containing aldehyde group (-CHO)
- Ketoses: containing ketone group (-C=O)
Aldopentose
Ketohexose

Monosaccharides
• Pentoses
• Hexoses
• Deoxysugars

Pentoses
- Simple sugars.
- Five carbon atoms.
- Unfermentable by yeast.
- Give furfural when warmed with conc. acids.
- Rarely occur in free state but generally occur as
pentosans or form the sugar moiety of glycosides.

Pentoses
2
3
Apiose
HOH2C CH2OH
OH
CHO
OHH

Found in all plant and animal cells as
the carbohydrate part of nucleic acids.
e.g ribonucleic acid (RNA)
Xylose (or wood sugar): prepared
from corncobs, bran straw (or any
woody material) by boiling with acids,
fermenting any glucose present with
yeast and crystallizing the D-xylose
from the evaporated solution.

Apiose
Arabinose (or pectin sugar): found in
gums, pectic substances accompanying
hemicellulose and form the sugar part
of several glycosides.
Apiose is a rare sugar that is
interesting due to its unusual branched
structure. It is obtained by hydrolysis of
the flavone glycoside, apiin, which is
present in the leaves and seeds of
parsley.
HOH2C CH2OH
OH
CHO
OHH

OH
OH O
Apiose-Glu-O
HOH2C CH2OH
OH
CHO
OHH
Apiin
(present in the leaves of parsley)
Apiose

Chemical Tests for Pentoses
1- Aniline Acetate Test:
The furfural produced by the reaction of HCl on
pentoses forms a bright red color with aniline
acetate in a test paper held over the mouth of
the reaction flask.
Pentoses + HCl bright red color
with aniline acetate paper

2- Bial's (Orcinol) test
• Pentoses are converted to furfural by Bial’s
reagent (orcinol/HCl) green color.
Pentoses + (orcinol/HCl) green color

3- Tollen’s test
• Pentoses + tollen’s
reagent (phloroglucinol)
• red color
Pentoses + phloroglucin/HCl red color

Hexoses
- Simple sugars.
- Six carbon atoms.
- Fermentable by yeast.
- Give hydroxy-methyl furfural when warmed
with conc. acids.
- They occur free, combined as oligo- and
polysaccharides or forming the sugar part of
glycosides.

Hexoses
Aldohexoses Ketohexoses
-Glucose
-Mannose
-Galactose
-Fructose

Aldohexoses
Glucose
• Source:
• D-glucose is found free in sugar juices or forms
the sugar part of many glycosides.
• Physical properties:
• Condition: white crystalline.
• Taste: sweet.
• Solubility: soluble in water.

Conversion of glucose to the cyclic (pyranose) form
1
2
3
4
5
Haworth projections.Fischer projection

For sugars with more than one chiral center, the D or L designation
refers to the asymmetric carbon farthest from the aldehyde or
keto group.

• Most naturally occurring sugars are D isomers.
• D & L sugars are mirror images of one another.

• Chemical properties:
• 1- reduces Fehling’s and Barfoed’s reagents.
• 2- it gives positive Osazone test.
• Uses:
• 1- of great pharmaceutical importance as
ingredient in I.V injections as nutrient, diuretic
and sweetening agent.
• 2- used in ice-cream and candy industries.

Mannose
• It C-2 epimer (mirror image) of glucose.
• Doesn’t occur free in nature but as a
constituent of many polysaccharides.
• Prepared from the seeds of date, coffee and
from ivory nuts during the manufacture of
buttons by acid hydrolysis.
• It gives an osazone similar to that of glucose.

Galactose
• It is the C-4 epimer of glucose.
• Occurs as the sugar part of several
glycosides.
• A constituent of many polysaccharides
e.g. agar-agar, linseed mucilage…..etc.
• Prepared by acid hydrolysis of agar or
linseed.

Ketohexoses
Fructose
(levulose or fruit sugar)
• Source:
• Found free in honey and in fruit juices or as a
constituent of polysaccharide e.g. inulin.
• Physical properties:
• Condition: colourless crystals.
• Taste: intense sweet taste.
• Solubility: soluble in water.

• Chemical properties:
• 1- reduces Fehling’s and Barfoed’s reagents.
• 2- it gives positive Osazone test similar to that of glucose.
• 3- Seliwanoff's (Resorcinol) Test (used for detection ketoses)
• a chemical test which distinguishes between aldose and ketose sugars.
• The reagents consist of resorcinol and concentrated hydrochloric acid.
• Ketohexoses (such as fructose) a cherry-red
condensation product.

Uses:
• 1- as food for diabetics (in emergencies of diabetic
acidosis).
• 2- in infant feeding formulae (more easily digested
than glucose).

Deoxysugars
(Desoxysugars)
• Commonly derived from hexoses by removal of
oxygen atoms from either carbon 2 or 6 or both
carbons 2 and 6 to produce 2-
deoxy or 2,6- deoxyhexoses

2-Deoxypentoses
• Example: 2-Deoxy-D-ribose
• (DNA).
2 2

6-Deoxyhexoses
• (methyl pentoses or hexomethyloses):
• Example: α-L-Rhamnose (6-deoxy-L-mannose)
• 2,6-deoxysugars give positive Keller-Kiliani’s
test.
6
6

• Keller-Kiliani’s test
Glycoside + CH3COOH + H2SO4 + FeCl3 brown colour

Derivatives of Hexoses
• The naturally occuring derivatives of hexoses of
pharmaceutical importance are the sugar
alcohols e.g. sorbitol and mannitol.
• Sugar Alcohols
• ex: Sorbitol and Mannitol
• Preparation:
• Sorbitol is prepared by reduction of glucose and
mannitol by reduction of mannose.
• Therefore, mannitol is the C-2 epimer of sorbitol.

• Uses:
• Sorbitol is used as a mild laxative, in preparation
of spans and tweens, and in some food and
cosmetics industries.
• Mannitol is used as an osmotic diuretic,
vasodilator and in laboratory diagnosis of kidney
function (mannitol hexanitrate).

Sugar Acids
ex: Gluconic acid and its salts
• Preparation:
• Gluconic acid is prepared from glucose by mild
oxidation using either dilute HNO3 or Br2/Na2CO3 or
by fermentation using Acetobacter aceti.
• Uses:
• Ca gluconate is used (by i.v or oraly) for treatment of
calcium defficiency.
• Ferrous gluconate (orally or by i.v) is used in iron
defficiency.
• N.B These salts are characterized by being more
readily absorbed than other Ca or Fe salts.

Carbohydrates Characterization
• Molisch’s Test : carbohydrate
• Benedict’ s Test : color change indicator for
simple sugars
• Fehling Test: Reducing sugars
• Barfoed’s Test: Monosaccharides and
Oligosaccharides
• Seliwanoff Test : Differentiation of Ketose from
Aldose
• Iodine Test : Cellulose, Starch, Dextrin

Oligosaccharides
• Properties:
- Crystalline and soluble in water.
- Hydrolysable by acids or specific enzymes to
yield from 2-10 molecules of monosaccharides.
- Monosaccharide units are linked through
glycosidic linkages.
- They are sub-classified on the basis of the
number of sugar molecules into di-, tri-, or
tetrasaccharides.

1- Identification of the type of
monosaccharide or sugar units
• Acid hydrolysis
one single sugar homotype of
oligosaccharides.
different sugars heterotype of
oligosaccharides.
Then individual sugars are identified by
chromatography.

• 2- Determination of the type of the glycosidic
linkage between the sugar units:
• The position and the stereoisomeric form
(configuration) of the linkage shlould be
determined.

Disaccharides
Non-reducing Reducing
- Sucrose - Lactose
- Maltose

Non-reducing sugars
Sucrose
- Most widely occuring disaccharide.
- Found in many fruit juices, seeds, leaves, roots
and honey.
• Properties:
- readily soluble in water.
- sweetening power more than glucose and less
than fructose.
- heating 200-250°C Caramel ( a
decomposition product widely used as a
flavoring and colouring matter.

• Seliwanoff’s test rapid furfural.
• doesn’t reduce Fehling’s solution.
• doesn’t form osazone.
• Uses:
- In pharmaceutical preparations: in syrup
preparations & tablet manufacture.
- As a nutrient and demulcent.
- In preparation of dextran (a polysaccharide used
as plasma substitute).

Reducing disaccharides
• The reducing properties are due to the
presence of free hemiacetal group in their
molecule.
• Reducing dihexoses are classified according to
the site (or position) of the linkage into:
• C1- C3
• C1-C4
• C1-C6

Lactose (milk sugar)
• Source:
- It is the principal sugar of mammalian milk.
- not present in higher plants.
• Structure:
• It consists of galactose and glucose linked by β1-4
linkage.
• It is hydrolysed by β-galactosidases

• Properties:
- It forms a characteristic osazone (needles
aggregated in clusters or tufts).
• Lactose intolerance:
• defficiency of lactase enzyme.

• Uses:
- As nutrient in infants food, since it is less sweet
than sucrose and more easily digested.
- also used as inert diluent for other drugs.

Trisaccharides
Raffinose
• Source:
- is a non-reducing trisaccharide.
- Found in beet, cottonseed and soyabean.

Polysaccharides
• They are complex, high molecular weight
monosaccharide polymers of very wide
distribution in nature.
• ex: cellulose and chitin that are found as skeletal
material of plants and animals.
• Starch and glycogen occur as metabolic reserve
substances, readily convertibles when energy is
required.

Polysaccharides
Homosaccharides
(holosides)
Heterosaccharides
(heterosides)
similar
monosaccharide units
different
monosaccharide units
Glucans Fructosans

Homosaccharides
(Homopolysaccharides or Holosides)
• Glucans as starch, dextrin, dextran,
sephadex, glycogen and cellulose.
• Fructosans as inulin.

The glucans
Starch
• Source:
• The most abundant and widely distributed
plant substance.
• occurs as microscopic granules in the seeds,
fruits, tubers and roots of plants.
• The most common commercial sources are
the graminaceous grains such as rice, wheat
and maize.

• Structure:
- It is an α- glucan (α-glucosan) polysaccharide.
- The final product of hydrolysis is glucose.
- On heating starch with water colloidal
suspension two major components can
be isolated amylose & amylopectin

Separation of starch components:
• Hot aqueous starch solution + n-butanol
ppt. of Amylose
• The mother liquor + Methanol
ppt. of Amylopectin
cooling

• Amylose:
• Amylose is made up of α(1→4) bound glucose
molecules.
• forms the inner layers of the starch granules.
• soluble in water.
• gives blue colour with iodine solution.
n > 100

• Amylopectin:
• forms the outer layers of the starch granules.
• sparingly soluble in water.
• gives bluish colour with iodine.

• Uses:
- Dusting powder.
- Antidote for iodine poisoning.
- Diluent in powders and tablets manufacture.
- Nutrient, demulcent, protective and
adsorbent.
- Starting material in the manufacture of
glucose, liquid glucose, maltose and dextrins.

2- Dextrins (artificial gums)
• Source:
• Polymer of 8-glucose units.
- could be prepared by partial starch hydrolysis by:
- Enzymatic degradation using β-amylase.
• prepared by acid and heat -> white dextrin
• or just heat (roasting starch) -> yellow dextrin
• white has less adhesive properties
–smaller molecule since partly broken down
by acid
• Main use:
–adhesive dressings
–food products (binding – pastes, thickeners)

3- Dextrans
• not starch
• polymer of 1,6 links of glucose units
• formed from sucrose by the action of a bacterial
enzyme obtained from Leuconostic mesenteroides
converts sucrose -> α 1,6 glucose dextrans
• Uses:
–as blood plasma expanders (severe
haemorrhage, bad burns)
–as adhesives and cosmetic powders (stick to
moist skin)
–Dextran sulphate used as anticoagulant, in
treatment of ulcer and in preparation of
sephadex.

4- Sephadex
• Source:
- modified dextran.
- Dextran macromolecules are cross-linked to give
a three dimensional network of polysaccharide
chains.
• Properties:
- water insoluble
- strongly hydrophilic (its beads swell in water,
the degree of swelling is varied to give different
types of sephadex gels.

• Uses:
- Chromatographic separation of biological
compounds, e.g. enzymes, proteins and
carbohydrates and as a molecular sieve.

5- Glycogen (or animal starch)
- The principal reserve polysaccharide of
animals
- found in muscles and liver.
- Also occurs in certain fungi, algae and
bacteria.

6- Cellulose
- The main constituent of cell walls of plants
associated with other polysaccharides such as
hemicellulose or with non-carbohydrate
substances such as lignin.
- has β-1,4 links (1,4-β-D-glucopyranosyl units)

The fructosans
Inulin
• Inulin is a collection of fructose polymers. It
consists of glucosyl moiety and fructosyl
moiety, which are linked by β(1-2) bonds.
• fructose polymer
• stored in some plants as an alternative food
reserve to starch
• Inulin is a plant starch in subterranean
organs.

Heterosaccharides
(Heteropolysaccharides or Heterosides)
• These are polysaccharides which contain either:
- (a) Dissimilar monosaccharide building units.
- (b) Monosaccharides together with their
sulphate esters, uronic acids or amino
derivatives.

Cellulosans
- a type of hemicellulose.
- formed of short chain polysaccharides.
- They are either simple pentosans e.g xylans or
hexosans e.g. glucans, mannans or galactans.
- They accompany cellulose and lignin in plant
cell walls.

Derived carbohydrates
Polyuronides
• Examples:
- Hemicellulose.
- Plant gums.
- Mucilages
- Pectic substances.

Plant gums
- are polysaccharides exuded from certain plants
as pathological products in response to injury
or unfavorable conditions, e.g. Gum arabic
and gum tragacanth.

Wounding of
branches and gum
exudate

Gum Arabic (Gum Acacia)
• It is the dried gummy
exudate obtained by
incision from stems and
branches of Acacia
senegal, Family:
Leguminoseae

• Constituents:
1- Arabin: a complex mixture of calcium,
magnesium and potassium salts of Arabic
acid.
Arabic acid: branched polysaccharide with the
basic building unit is galactose.
2- enzymes: oxidases, peroxidases and
pectinases.
• Uses:
1- Emulsifying and suspending agent.
2- demulcent and emollient.
3- adhesive and binder in tablet manufacture.

b- Gum Tragacanth
Origin:
• the air hardened gummy
exudates obtained by
incision from Astragalus
gummifer and other
Asiatic species of
Astragalus, Family:
Leguminosae

• Solubility:
• slightly soluble in water, swelling at first into a
homogeneous adhesive mass. It is insoluble in
ethanol.
• Constituents:
1- Bassorin: a complex of polyhydroxylated acids
2- Tragacanthin: demethoxylated bassorin

• Chemical tests:
1- aqueous solution + HCl, heat for 30 min., divide into two
portions:
a- add NaOH and potassium copper tartarate, heat in W.B. → red
ppt
b- add BaCl2 → no ppt (agar).
2- solution in water + barium hydroxide → slight flocculent ppt ,
heat → yellow colour.
• Uses:
As gum arabic, but due to its resistance to acid hydrolysis it is
preferred for use in highly acidic conditions.

MUCILAGE
- are generally normal
products of metabolism
formed within the cell
(intracellular formation).
Function of Mucilage:
- Storage material.
- Water storage reservoir.
- Protection for germinating
seeds.

• Properties:
- white amorphous masses.
- swell in water and form viscous non-adhesive
solutions.
- have variable physical and chemical properties.
• Classification:
- The neutral mucilages.
- The acidic mucilages as mustard &plantago.
- The sea weed mucilages as agar.

Natural sweeteners Artificial sweeteners
Bulk sweeteners Intense sweeteners
Ex:
- Cyclamate
- Aspartame
- Saccharin
Ex:
- Sorbitol
Ex:
- Glycyrrhizin

Carbohydrates

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