Carbohydrates are essentially substances that are made up of carbon, hydrogen and oxygen only. The carbohydrates are divided into three broad categories, namely, monosaccharides, oligosaccharides and polysaccharides. Carbohydrates function as lubricants in skeletal joints and help the cells to stick with each other and remain in place.

1. Mrs. R.Subha, M.Sc., M.Phil., D.C.T.,
Assistant Professor of Home Science

2.  Carbohydrates are essentially substances that are made
up of carbon, hydrogen and oxygen only.
 The carbohydrates are divided into three broad
categories, namely, monosaccharides, oligosaccharides
and polysaccharides.
 Monosaccharides represent the group of carbohydrates
that cannot be further hydrolyzed to smaller molecules.
They form the building blocks of the more complex
carbohydrates.
 Oligosaccharides comprise the low molecular weight
polymers that include the disaccharides and
trisaccharides and compounds with as many as ten
monosaccharides linked into single molecules.

3. Polysaccharides are the carbohydrates which contain more than 10
monosaccharide units.They can be hydrolyzed into hundred or even thousands
of monosaccharide units.
The suffix –ose in sugar is changed to –ans to describe the corresponding
polysaccharide.
Examples:
(1) Pentosans
(a)Arabans
(b) Xylans
(2) Hexosans
(a) Glucans à starch, dextrin, glycogen, cellulose, inulin
(b) Mannans
(c) Galactans
(3) Complex polysaccharides
(a) Pectins or pectic substances
(b) Gums
(c) Mucilages
(d) Algal polysaccharides à Alginic acid and carrageenan.
(e) Bacterial polysaccharides à Xanthan gum.

5.  defined as polyhydroxy aldehydes or ketones and
their derivatives.
 Their general formula can be represented as
Cx(H2O)y.
 Carbohydrates are formed in plant cells from
carbon dioxide and water in a process called as
photosynthesis.
 1 g of carbohydrates provide 4 kcal energy.
 In human food, the sources of carbohydrates are
cereals, roots, tubers, sugarcane and sugarbeet.
 Carbohydrates are named according to sources
from which they are obtained e.g., fructose (fruit
sugar), lactose (milk sugar), xylose (wood sugar)
and cellulose (from cell membrane).

6.  Most of the monosaccharides, disaccharides
and lower polysaccharides are sweet in taste,
whereas starch and cellulose are tasteless.
 They exhibit stereoisomerism. Stereoisomers
are compounds whose structural formula is
same but arrangement of atoms in 3-
Dimensional space is different. E.g., with
respect to Carbon no. 5, Glucose has two
forms, D-glucose and L-glucose.

7.  They exhibit optical activity. (Optical
activity is a phenomenon in which a
molecule rotates plane of plain
polarised light. If the molecule
rotates the plane towards left, it is
designated levo rotatory (- sign) and
if the plane is rotated towards right,
the molecule is designated dextro
rotatory (+ sign). D-glucose rotates
plane of plain polarised light towards
right while L-fructose rotates it
towards left.

8.  The sugars in which free aldehyde or ketone
groups are present can reduce Fehling’s
solution and Benedict’s solution are called
reducing sugars. The sugars in which free
aldehyde or ketone groups are absent are
called as non-reducing sugars. Glucose,
fructose, lactose etc., are reducing sugars
whereas sucrose is a non-reducing sugar.

9.  They are a major part of total caloric intake.
 Starch and glycogen serve as temporary
stores of glucose.
 Water insoluble carbohydrates are major
components of cell wall in plant cells and cell
membrane in animal cells.
 Carbohydrates function as lubricants in
skeletal joints and help the cells to stick with
each other and remain in place.

10.  Satyanarayana U. & Chakrapani U. (2011),
“Biochemistry”. Books and Allied (P) Ltd. pp.
 N. Shakuntala Manay & M. Shadaksharaswamy
(2001), “Foods: Facts and Principles”. New Age
International Publishers.