• A disaccharide, also called a double sugar, is a
molecule formed by two monosaccharides, or
• Three common disaccharides are sucrose, maltose,
• Disaccharides are formed through dehydration
reactions in which one water molecule is removed
from the two monosaccharides.
• They have 12 carbon atoms, and their
chemical formula is C12H22O11.
• Other, less common disaccharides include
lactulose, trehalose, and cellobiose
• Maltose, also known as malt sugar, is formed
from two glucose molecules.
• Malt is formed when grains soften and grow in
water, and it is a component of beer, starchy
foods like cereal, pasta, and potatoes, and
many sweetened processed foods.
• Beverages : maltova, boost, horlicks etc.
• In plants, maltose is formed when starch is
broken down for food. It is used by
germinating seeds in order to grow.
• Like maltose, cellobiose is also made up
of two glucose molecules, but they are
linked in yet another different way.
• It is found when cellulose, the main
component of plant cell walls, is
• Cellobiose is used in bacteriology to
perform chemical analyses.
• Lactose, or milk sugar, is made up of
galactose and glucose. The milk of
mammals is high in lactose and provides
nutrients for infants.
• Most mammals can only digest lactose as
infants, and lose this ability as they
Sucrose : Sucrose, commonly known as table
sugar in its refined form, is a disaccharide
found in many plants. It is made up of the
monosaccharides glucose and fructose. In
the form of sugar, sucrose is a very important
component of the human diet as a sweetener.
Sucrose - 100
Glucose - 70
Fructose - 170
Lactose - 30
• Lactulose : Lactulose is formed from fructose
and galactose. It can be used to treat
constipation and liver disease
• Trehalose : Trehalose is also made up of two
glucose molecules like maltose, but the
molecules are linked differently. It is found in
certain plants, fungi, and animals like shrimp
• The blood sugar of many insects, such as
bees, grasshoppers, and butterflies, is made
up of trehalose. They use it as an efficient
storage molecule that provides rapid energy
for flight when broken down.
• Oligosaccharides are carbohydrates that
yield two to ten monosaccharide units on
• Raffinose and stachyose are two
important oligosaccharides present in
dried beans, peas and lentils, which yield
three monosaccharide units on hydrolysis.
STRUCTURE OF OLIGOSACCHARIDES
• Raffinose, also called melitose, is a
trisaccharide that is widely found in
legumes and cruciferous vegetables,
including beans, peas, cabbage, brussels
sprouts, and broccoli.
• It consists of galactose connected to
sucrose via a α1→6 glycosidic linkage.
• Humans cannot digest polysaccharides with
this linkage and the trisaccharides are
fermented in the large intestine by gas-
• Polysaccharides are long carbohydrate chains
that yield more than ten molecules of
monosaccharide on hydrolysis.
• Examples of polysaccharides are : glycogen,
starch, cellulose and dextrin.
• These are sometimes designated as hexosans
or pentosans, depending upon the number of
the monosaccharides they yield on hydrolysis.
• They are called GLYCANS and NON-SUGARS
STRUCTURE OF POLYSACCHARIDES
• Starch is a polymer of glucose linked by
α (1- 4) - glycosidic bond. (like maltose)
• It yields only glucose on hydrolysis and
hence is a homopolymer and is called a
glucosan or glucan.
• It is the most important food source of
carbohydrate and is found in cereals,
potatoes, legumes and other vegetables.
• The two chief constituents of starch are amylose
(15-20%) and amylopectin (80-85%).
• Amylose has a non branching helical structure.
• Amylopectin consists of branched chains
composed of 24-30 glucose residues united by
α(1-4) linkages in the chains and by α(1-6) linkages
at the branch points
• Rich sources of starch are :
grains - wheat, rice, corn, oats, millets & barley
legumes - peas, beans and lentils
tubers - potatoes, yam and cassava
• Glycogen is the storage polysaccharides of the
animals. So often called - animal starch.
• Its structure is similar to amylopectin, but it is
• It has chains of 12-14 -D-glucopyranose
residues (in -[1-4] - glycosidic bond) with the
branching by -(1-6 ) - glycosidic bonds
• Skeletal muscle and the liver are the two
important sites of glycogen storage.
• Cellulose is the chief constituent of the
structure of plants.
• It is insoluble and consists of D-
glucopyranose units linked by (1-4)
glycosidic bonds (similar to cellobiose) to
form long, straight chains strengthened by
cross-linked hydrogen bonds.
• Cellulose cannot be digested by many
mammals, including humans, because of
the absence of an enzyme that attacks the
• But, it is an important source of “bulk” in
the diet. In the stomach of ruminants and
other herbivores, there are
microorganisms that can attack the
linkage, making cellulose available as a
major source of energy.
• Chitin is an important structural
polysaccharide of invertebrates.
• It is found in the exoskeletons of
crustaceans and insects.
• Structurally, chitin consists of :
N - acetyl - D- glucosamine units
joined by (1-4)-glycosidic bond.
• Pectin occurs widespread in nature but is
found especially in the pulp of citrus fruits,
apples, beets and carrots.
• The term ‘Pectin’ represents the substances
which in the presence of sugar and proper acid
concentration causes the formation of jellies.
• Because of its ability to form a thick gel-like solution, pectin
is used commercially in the preparation of jellies, jams, and
• Its thickening properties also make it useful in the
confectionery, pharmaceutical, and textile industries
• Pectin is combined with cellulose in the cell
walls, from which it may be released by mild
hydrolysis and converted into soluble
• The combined, insoluble pectin is referred
to as proptopectin.
• When soluble pectin is boiled with dilute
acid, it is slowly hydrolyzed to pectic acid
and methyl alcohol.
• Purified pectin accordingly is the methyl ester
(many methyl groups per molecule) of pectic
• Pectic acid is a chain of at least 200 of (1-4)
linked a-D galactopyranosyl uronic acid units.
• Because of its ability to form a thick gel-like
solution, pectin is used commercially in the
preparation of jellies, jams, and marmalades.
• Its thickening properties also make it useful
in the confectionery, pharmaceutical, and
• Pectin also has several health benefits in
• Included among these are its ability to reduce
low density lipoprotein (LDL) levels, thereby
lowering cholesterol levels, and its ability to
slow the passage of food through the intestine,
• Pectin can also activate cell death pathways in
cancer cells, indicating that pectin may play an
important role in preventing certain types of