Introduction to fats & oils
Session Objectives
By the end of this session, students will be able to:
Ø Classify
fats & oils
Ø Discuss
nomenclature of Fatty acids
Introduction
The word lipid is derived from Greek word lipos meaning fats
Play important role in cellular structure and also have
various other biochemical functions
Lipids are the chief concentrated storage form of energy
Lipids are heterogenous group of compounds
Lipids may be regarded as organic substances relatively
insoluble in water, soluble in organic solvents (alcohol, ether etc.), actually
or potentially related to fatty acids and utilized by the living cells
Unlike the polysaccharides, proteins and nucleic acids,
lipids are not polymers. Further, lipids are mostly small molecules
• Made from esters of propane-1,2,3,triol
(glycerol) + long chain carboxylic acids RCOOH.
• Common fatty acids
Classification of lipids
Lipids are broadly classified into simple, complex, derived
and miscellaneous lipids, which are further subdivided into different groups
1) Simple lipids: esters of fatty acids with alcohols
These
are mainly of two types
A) Fats
and oils B) waxes
A) Fats and oils:
·
Are esters of fatty acids with glycerol
·
The difference between fat and oil is only
physical
·
Oil is a liquid while fat is a solid at room
temperature
B) Waxes
·
Esters of fatty acids (usually long chain) with
alcohols other than glycerol
·
These alcohols may be aliphatic or alicyclic
·
Cetyl alcohol is most commonly found in waxes
2) Complex (or Compound) lipids
These
are esters of fatty acids with alcohols containing additional groups such as
phosphate, nitrogenous base,
carbohydrate, protein etc.
They are further divided as follows
(a) Phospholipids: Contain phosphoric acid and
frequently a nitrogenous base, This is in addition to alcohol and fatty acids.
Types of Phospholipids
(i) Glycerophospholipids:
These phospholipids contain glycerol as the alcohol
Eg: lecithin, cephalin
(ii) Sphingophospholipids:
Sphingosine is the alcohol in this group of phospholipids
Eg: sphingomyelin
(b) Glycolipids: These lipids contain a fatty acid,
carbohydrate and nitrogenous base.
·
The alcohol is sphingosine, hence they are also
called as glycosphingolipids.
·
Glycerol and phosphate are absent e.g.,
cerebrosides, gangliosides
(c) Lipoproteins: Macromolecular complexes of lipids
with proteins.
(d) Other complex lipids: Sulfolipids, aminolipids
and lipopolysaccharides are among the other complex lipids.
3) Derived lipids: These are the derivatives obtained
on the hydrolysis of group 1 and group 2 lipids which possess the
characteristics of lipids
These include glycerol and other alcohols, fatty acids,
mono- and diacylglycerols, lipid (fat) soluble vitamins, steroid hormones,
hydrocarbons and ketone bodies
4) Miscellaneous lipids: These include a large number
of compounds possessing the characteristics of lipids
Eg: carotenoids, squalene, hydrocarbons such as pentacosane (in bees wax),
terpenes etc.
Neutral
Lipids: The lipids which are uncharged are referred to as neutral lipids
These are mono-, di-, and triacylglycerols, cholesterol and
cholesteryl esters
Fatty acids
·
Fatty acids are carboxylic acids with
hydrocarbon side chain
·
They are the simplest form of lipids
Occurrence:
·
Fatty acids mainly occur in the esterified form
as major constituents of various lipids
·
They are also present as free (unesterified)
fatty acids
·
Fatty acids of animal origin are much simpler in
structure in contrast to those of plant origin
·
Contain groups such as epoxy, keto, hydroxy and
cyclopentane rings
·
Even and
odd carbon fatty acids
·
Most of the fatty acids that occur in natural
lipids are of even carbons (usually 14C- 2OC)
·
This is due to the fact that biosynthesis of
fatty acids mainly occurs with the sequential addition of 2 carbon units
·
Palmitic acid (l6C) and stearic acid (l8C) are
the most common
·
Among the odd chain fatty acids, propionic acid
(3C) and valeric acid (5C) are well known
Saturated and Unsaturated fatty acids:
·
Saturated fatty acids do not contain double
bonds,
·
while unsaturated fatty acids contain one or
more double bonds
Saturated and Unsaturated fatty acids:
·
Both saturated and unsaturated fatty acids
almost equally occur in the natural lipids
·
Fatty acids with one double bond are
monounsaturated and those with 2 or more double bonds are collectively known as
polyunsaturated fatty acids (PUFA)
Nomenclature of fatty acids:
·
Naming of fatty acid is based on hydrocarbon
from which it is derived suffix will be
–ic acid
·
Saturated fatty acid eg: Butyric (butanoic
acid): CH3(CH2)2COOH
·
Unsaturated fatty acid eg: Oleic acid: CH3(CH2)5CH=CH(CH2)7COOH
·
In addition to that, fatty acids have some
common names
Numbering of carbon atoms:
·
It starts from carboxyl carbon which is taken as
number 1
·
The carbons adjacent to this (carboxyl C) are 2,
3, 4 and so on or alternately a, β,
γ and so on
·
The terminal carbon containing methyl group is
known omega (ω) carbon
·
Starting from the methyl end, the carbon atoms
in a fatty acid are numbered as omega 1, 2, 3 etc.
·
The numbering of carbon atoms in two different
ways is given below
Summary
• Lipids
are the chief concentrated storage form of energy
• Lipids
are heterogenous group of compounds
• Oil
is a liquid while fat is a solid at room temperature
• Fatty
acids are carboxylic acids with hydrocarbon side chain
• Most
of the fatty acids that occur in natural lipids are of even carbons (usually
14C- 2OC)
• Naming
of fatty acid is based on hydrocarbon from which it is derived
• Numbering
starts from carboxyl carbon which is taken as number 1
