Disaccharides
Maltose
• Maltose is combination of glucose +glucose
• The 2 molecule of glucose are attached by 1:4
linkage.
• One molecule of glucose is bound through
the hydroxyl groups of carbon atom No 1 of
one of the molecules to the hydroxyl groups
of carbon atom No 4 of the second molecule
of glucose.
Maltose
Maltose
• It is the end product of digestion of starch by
ptyalin and it is the chief sugar of malt.
• It is reducing sugar due to the presence of a
free aldehyde group.
• It gives osazone test which splits on cooling.
• Molisch’s and Fehling tests are positive. It is
dextrorotatory.
• It is fermented by yeast due to the presence of
maltase enzyme
Maltose
• It is not sweeter than glucose or fructose.
• It hydrolyzed by maltase enzyme and dilute
HCl.
• Maltose is present in germinating barely (malt
sugar).
Lactose (milk sugar)
• It is composed of one molecule of glucose and
one molecule of galactose.They are united in a
glucosidic 1:4 linkage with a net result that the
aldehydic group of galactose is destroyed
while that of glucose remains free.
• It is only in animal origin.
• It gives +ve Molisch’s test, +ve reduction test
and gives a specific osazone test splits on
cooling.
Lactose
• It is optically active and it is dextrorotary.
• It appears in the urine of the lactating women.
• It is not fermentable sugar due to the absence
of lactase enzyme.
• By conc. HNO3 it gives mixture of mucic and
saccharic acids.
• Lactobacillus acidophillus bacteris changes
lactose to lactic acid.
Lactose
Lactose fermentation
Bacteria
Lactose
Water
Lactic
acid
Lactose
• If milk is exposed to atmosphere, souring
happens and caseinogen is precipitated due to
the acidity formed as a result of formation of
lactic acid.
• It is hydrolyzed by lactase enzyme giving rise
to glucose + galactose
Lactose intolerance
• Infants normally have the intestinal enzyme
beta-D-glucosidase (lactase) that catalyzes
the hydrolysis of lactose to its component
monosachharides for absorption into the
blood stream.
• Much of the lactose in any milk they drink
moves through their digestive tract to the
colon, where its bacterial fermentation
produces large quantities of CO2, H2 and
irritating organic acids which leads to painful
Sucrose (cane sugar)
• It is formed of the union of one
molecule of glucose and fructose in a
way that both the aldehydic and ketonic
groups are destroyed.
Glucose
Fructose
Sucrose
sucrose
• It is the common sugar used at home.
• It is non-reducing sugar. It gives no osazone
test.It is like all CHO gives +ve Molisch’s test.
• It is optically active and it is dextrorotary. On
hydrolysis it gives equal amount of glucose
and fructose.
• The whole solution after hydrolysis is
inverted from being dextro to laevorotary.
• The enzyme hydrolysing sucrose is called
invertase.
sucrose
• The equal mixture of glucose and fructose is
called invert sugar.
• Honey is chiefly invert sugar and the presence
of fructose is the cause of its greater
sweetness.
• It is fermented by yeast
• It is present free in cane sugar, carrots and
certain fruits.
Trisaccharides
• It is composed by the union of 3 molecules of
monosaccharides (raffinose).
• (glucose+ galactose+ fructose) with the
elimination of 2 molecules of water.
• It is present in cotton seed oil and some
cereals.
• It is non reducing sugar and it is dextrorotary.
• On hydrolysis it gives mixture of glucose,
galactose and fructose.
• 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 1α→6 glycosidic linkage. Humans cannot
digest saccharides with this linkage and the
saccharides are fermented in the large
intestine by gas-producing bacteria.
Raffinose
Polysachharides
Homopolysachharide
s
Glucans
Galactosans
Polymers of
glucose
Polymers of
galactose
Heteropolysacchrides
polysaccharides
• All polysaccharides are formed of a great
number of monosaccharide.
• All polysaccharides are non reducing sugar.
• Optically active.
• It gives negative Fehling and Bendict tests.
• The monosaccharide entering in the formation
of polysaccharides are attached together in
glucosidic linkage (1:4 or 1:6).
• They form long chains which may be linear
form as in case of cellulose or branched
structures as in glycogen and starch.
• Some members give violet or blue color with
iodine solution.
• Some are soluble in hot water, starch and
some are insoluble as cellulose.
Classification of polysachharides
Pentosans
Formed by condensation of
pentoses, araban and xylan
Hexosans
Glucosans
(starch,cellulose,glycogen,dext
rin)
Fructosans (inulin).
Mixed polysachharides
Complex polysaccharides
(pectin,heparin, Hyaluronic
acid
starch
• It represents the reseve food in plants
• Insoluble in cold water,it is soluble in hot
water.
Starch granules
are formed from
Amylopectin
Amylose
Starch molecule
starch
starch
• Amylopectin: present in the outer layer of the
granule.The molecule of amylopectin is
branched. The branch is formed about
25glucose units.
• The glucose unit are linked together by alpha
glucosidic 1:4 linkage,the linkage between the
branches is through 1:6 glucosidic linkage.
• Amylose: forms the inner layer of the granule.
• Other polysachharides includes
dextrins,dextran,glycogen cellulose, inulin and
hemicellulose and pectins.