2. Lipids may be defined as organic substances
which are relatively insoluble in water, but
freely soluble in nonpolar organic solvents
like benzene, chloroform, ether, acetone etc.
3. According to Bloor, lipids are compounds having the
Insoluble in water
Solubility in one or more organic solvents, such as
ether, chloroform, benzene, acetone etc
Some relationship to the fatty acids as esters either
actual or potential
Possibility of utilization by living organisms
5. Storage form of energy (Triacylglycerol)
Structural components of biomembranes
(phospholipids & cholesterol)
Metabolic regulators (steroid hormones &
Act as surfactants, detergents & emulsifying agents
6. Act as electric insulators in neurons
Provide insulation against changes in external
Give shape & contour to the body
Protect internal organs by providing a cushioning effect
(pads of fat)
Help in absorption of fat soluble vitamins (A,D,E & K)
Improve taste & palatability of food
7. Esters of fatty acids with glycerol or other higher
Simple lipids are: waxes & triacylglycerols
Esters of fatty acids with higher monohydroxy aliphatic
Cetyl alcohol (C16H33OH) is most commonly found in
• Liquids at 20oC
• contain a higher proportion of unsaturated
fatty acids or short chain triglycerides.
• Generally plant origin.
• solids at room temperature
• contain mainly saturated long chain fatty acids
• mainly of animal origin
12. Physical properties
1. Neutral fats colourless, odourless & tasteless
substances. The colour & taste of some of the
naturally occurring fats is due to extraneous
2. Solubility: Insoluble in water but soluble in organic
3. Specific gravity: less than 1.0
13. 4. Emulsification: Emulsions of fat may be made by
shaking vigorously in water & by emulsifying agents
such as gums, soaps & proteins which produce more
when the constituent fatty acids have a higher chain
length & are predominantly saturated, hard fat is formed
eg. Pig fat
Fat containing medium chain triglycerides or unsaturated
fatty acids are soft fats e.g. butter, coconut oil.
15. Hydrolysis with a strong base
Triglycerides split into glycerol and the salts of
The salts of fatty acids are “soaps”
KOH gives softer soaps
+ Na+ -
O C (CH2)14CH3
+ 3 NaOH
salts of fatty acids (soaps)
17. Refers to the appearance of an unpleasant smell &
taste for fats & oils.
It occurs when fat & oils are exposed to air, moisture,
light, bacteria etc.
1. Hydrolytic rancidity : due to partial hydrolysis of
the TG molecules due to traces of hydrolytic
enzymes present in naturally occurring fats & oils.
18. 2. Oxidative rancidity: is the partial oxidation of
unsaturated fatty acids. This results in formation of
unpleasant products such as dicarboxylic acids,
aldehydes, ketone etc.
19. The unsaturated fatty acids present in neutral fat exhibits
all the additive reactions i.e. hydrogenation, halogenation
etc. Oils which is liquid at ordinary temperature, on
hydrogenation become solidified.
Hydrogenation converts double bonds in oils to single bonds.
The solid products are used to make margarine and other
Defined as the number of mg of KOH required to hydrolyse
(saponify) one gram of fat or oil.
Measure of the average molecular size of the fatty acids present.
The value is higher for fats containing short chain fatty acids.
- Human fat : 195-200
- butter : 230-240
- coconut oil : 250-260
- Oleo-margarine : 195 or less
24. Defined as the number of mg of KOH required to
neutralize the fatty acids in a gm of fat or oil.
Significance: The acid number indicates the degree of
rancidity of the given fat.
25. Defined as the number of grams of iodine absorbed
by 100gm of fat or oil.
Measure the degree of unsaturation of a fat
The more the iodine number, the greater of
Useful in determination of quality of an oil or its
freedom from adultration
Fat or oil Iodine number
Coconut oil 7-10
Olive oil 80-85
Linseed oil 175-202
26. Defined as the number of ml of 0.1 normal KOH
required to neutrilize the insoluble fatty acids
(those not volatile with steam distillation) from
5gm of fat.
27. Defined as the number of ml of 0.1N alkali
required to neutrilize the soluble volatile fatty
acids distilled from 5g of fat.
Useful in testing the purity of butter since it
contains a good concetration of volatile fatty acids
(butyric, caproic & caprylic acid)
Butter : 25-30 (RM)
28. Defined as the number of mg of KOH required to
neutrilise the acetic acid obtained by
saponification of 1gm of fat after it has acetylated.
Measure of the number of –OH group present
Oils Acetyl number
Castor oil 146-150
Cotton seed oil 21-25
Olive oil 10.5