Lipids are a group of naturally occurring compounds that are insoluble in water but soluble in organic solvents. They are classified as simple lipids like oils and fats, compound lipids like phospholipids and sphingolipids, waxes, and derived lipids like fatty acids. Simple lipids are triglycerides composed of fatty acids and glycerol. Fatty acids can be saturated or unsaturated. Saturated fatty acids have only single bonds between carbon atoms while unsaturated fatty acids contain one or more double bonds. Cholesterol is found in animal tissues and serves as a precursor for bile acids, steroid hormones, and vitamin D.

1. Lipids
The term “lipids” applies to a group of naturally occurring substances which are insoluble in water but soluble in
non-polar solvents like chloroform, ether, benzene and carbon di sulphide. They occur widely in nature in either
free formor often associated with other compounds like proteins and carbohydrates.
Classification
Lipids are classified as follows:
1) simple lipids
2) compound lipids
3) waxes
4) derivedlipids
Simple lipids: These include oils and fats. These are esters of fatty acids and glycerol. It has been observed that
oils tend to remain liquid at 20C whereas fats tend to remain solid this temperature. A fatty acid is a long chain
carboxylic acid (CH3.(CH2)n.COOH. The fatty acids that are found in natural fats and oils have even number of
carbonatoms. The general structure of a fat molecule is:
C H2-O-OC- R1

2. C H-O-OC- R2
C H2-O-OC-R3
Where R1, R2, R3 are fatty acid components.
There are also known as “neutral fats” and are commonly found in adipose tissue, butter, lard, fish oil, olive olive
oile, corn oil, mustard oil and so on. The following reaction shows the formation of triglycerides form fatty acid
and glycerol:
Most fatty acids are linear but some branched chain and cyclic fatty acids are also found.
Check your progress:
1) What are lipids?
2) Classify lipids.
3) What are the functions of lipids?

3. SATURATED & UNSATURATED FATTY ACIDS
SATURATED FATTY ACIDS
The straight-chain (contain only single bond between carbon atoms) or normal-chain fatty acid components (that
are normally even numbered) make up 10 to 40% of the total fatty acids in mostnatural lipids. The most
abundantsaturated fatty acids in animal and plant tissues are straightchain compounds with 14, 16 and 18
carbon atoms. All the possible odd and even numbered homologues are found in esterified formin nature. They
are named systematically with saturated hydrocarbon with the same number of carbon atoms, the final ‘e’ being
changes to ‘oic’. Thus the fatty acid with 16 carbon atoms is systematically named as hexadecanoic acid. The
normal term used to describehexadecanoic acid in nutrition is palmitic acid. The structuralformula of palmitic
acid is as follows:
Itcan be also termed as C16 fatty acid or ‘16:0’ with a greater precision. The number beforethe colon specifies
the number of carbon atoms and the number after the colon species the position of the double bond.

4. The saturated fatty acids with more than 24 carbon atoms normally occur in foods and waxes. The fatty acids
present in milk fats contain 4 to 10 carbon atoms while those of chain length of C12 to C24 occur in mostanimal
and vegetable fats.
Some saturated fatty acids and their molecular formulaeare:
Butyric: CH3(CH2)2COOH
Lauric (dodecanoic acid): CH3 (CH2)10COOH
Myristic (tetradecanoic acid): CH3 (CH2)12COOH
Palmitic (hexadecanoic acid): CH3 (CH2)14COOH
StearicStearic acid also called octadecanoic acid is one of the many useful types of saturated fatty acids that come
frommany animal and vegetable fats and oils. Itis a waxy solid, and its chemical formula is CH(CH)COOH.
ArachidicArachidic acid also called eicosanoic acid is a saturated fatty acids found in peanut oil. It melts at 75. 4°C
and its chemical formula is CH(CH)COOH. (eicosanoic acid): CH3 (CH2)18COOH

5. UNSATURATED FATTY ACIDS
The unsaturated fatty acids contain double bonds between their carbon atoms. The number of double bonds may
vary fromone to six. The hydrogen atom is removed where the double bond is formed. The unsaturated fatty are
more vulnerableto rancidity. The unsaturated fatty acids are of two types:
MONOUNSATURATED FATTY ACIDS (MUFA):
The monounsaturated fatty acids contain only one double bond between the carbon atoms in a molecule of fatty
acid. For example, OLEIC ACID, PALMITOLEIC ACID, MYRISTOLEIC ACID.
The monounsaturated fatty acids have a higher melting temperature that the polyunsaturated fatty
acids but lower than the saturated fatty acids. They are liquid at roomtemperature and may become
semi-solid or solid when refrigerated.
POLYUNSATURATED FATTY ACIDS (PUFA) or ESSENTIAL FATTY ACIDS (EFA):
Fatty acids contain more than one double bond and are derived fromthose containing one double bond.

6. CLASSIFICATION OF PUFA:
LINOLEIC ACID FAMILY:
• LINOLENIC ACID (C18:2)
• γ-LINOLENIC ACID (C18:3)
• ARACHIDONIC ACID (C20:4)
LINOLENIC ACID FAMILY
• LINOLENIC ACID (C18:3)
• EICOSAPENTAENOIC ACID(C20:5)
• DECOSAHAEXOIC ACID(C22:6)

7. Fatty acid composition of fats and oils
Saturat
ed
Monounsatura
ted
Polyunsatura
ted
Choleste
rol
Vitam
in E
g/100g g/100g g/100g mg/100g mg/10
0g
Animalfats
Lard 40.8 43.8 9.6 93 0.00
Butter 54.0 19.8 2.6 230 2.00
Vegetablefats
Coconutoil 85.2 6.6 1.7 0 .66
Palm oil 45.3 41.6 8.3 0 33.12
Cottonseed
oil
25.5 21.3 48.1 0 42.77
Wheat germ
oil
18.8 15.9 60.7 0 136.65
Soya oil 14.5 23.2 56.5 0 16.29
Olive oil 14.0 69.7 11.2 0 5.10
Corn oil 12.7 24.7 57.8 0 17.24
Sunflower oil 11.9 20.2 63.0 0 49.0

8. Safflower oil 10.2 12.6 72.1 0 40.68
Hemp oil 10 15 75 0
Rapeseed/Can
ola oil
5.3 64.3 24.8 0 22.21
.
Compound lipids
1) Phospholipids: These are also known as phosphatides. They
contain phosphoric acid, nitrogenous base and glycerol and fatty
acids (lecithin, cepahiln etc)
2) Sphingolipids They contain s[hingosineor dihydrosphingosine
3) Glycolipids They contain carbohydrates along with fatty acids and
glycerol.
4) Sulpholipids: They contain sulphuric acid alon with fatty avids and
glycerol
Waxes (esters of fatty acids and long chain aliphatic alcohols)
Derivedlipids (fatty acids, alcohols and sterols)
FUNCTIONS OF FATS (TRIGLYCERIDES):
 Energy sourcein concentrated form (1gm provides 9kilocals of energy)
 Absorptionof fat soluble vitamins A,D,E,K
 Vegetarian fats good source of vitamin E; palm oil has ß-carotene
 Vegetarian fats are rich sources of EFA(LINOLEIC ACID)
 Reduces bulk of diet
 Palatability increases along with fullness in stomach
 Deposited in adiposetissue

9.  Insulation against cold especially in infants (BROWN ADIPOSE TISSUE)
FUNCTIONS OF SFA:
 Normally do not exceed 24 C-atoms in food triglycerides except in waxes
 C4 to C10 occurin milk fat
 C12 to C24 occur in animal and vegetarian fats
 Natural occurring SFA have even no. of C atoms; odd nos. comprise 1 to 2 %
 E.g.:
LAURIC ACID(12)
MYRISTIC (14)
PALMITIC (16)
STEARIC (18)
FUNCTIONS OF EFA/PUFA:
 DEFICIENCYMAY LEAD TO :
 Cessation in growth and development
 PHRYNODERMA or TOAD SKIN is presence of horny eruptions on the
posterior and lateral sides of the limbs, on the back and the buttocks.
TREATMENT includes administration of linseed oil + vitamin B2.
Other functions that adversely affected:
 Reproductionand lactation
 Integrity of cell membranes and cell functions
 Certain enzymatic reactions
 Transportof cholesterol
 Water balance
Deficiencyof PUFA in infants:
Irritation and changes in skin around anal region
Skin changes appear as dryness, thickening and desquamation

10. TREATMENT includes supplementation of linoleic acid for 2 weeks; and the
symptoms disappear.
Check your progress:
1) Describethe following:
a. EFA
b. MUFA
c. PUFA
d. SFA
CHOLESTEROL
 Occurs in all animal & human tissues
 White matter of brain contains about 14% white grey matter contains 6%
 Sebum from sebaceous glands also contain cholesterol
FUNCTIONS OF CHOLESTEROL
Serves as precursorin formation of bile acids
Present in cell membranes
Precursorof steroid hormones
Present in large amount in nervous tissue and resp for its function
Precursorof dehydrocholesterol (skin & other tissues) which is converted
to vit D3 by action of UV rays (sunlight).
CHOLESTEROLCONTENTOF FOODS
RICH SOURCES
Egg, hen (whole), egg yolk, liver, brain
GOOD SOURCES
Butter, ghee, cheese,lard & other animal fats, meat & fish
FAIR SOURCES
Milk (whole), milk powder(whole)
POOR SOURCES
Milk (skimmed), milk powder (skimmed)

11. Check your progress:
1) What is cholesterol?
2) What are the sources of cholesterol?
3) What are the functions of cholesterol?