Fats

1
Fats Oils

• Structure Properties
• Hydrolysis of Fats Oils
• Iodine Value
• Hardening of Vegetable Oil
• Hydrolytic Oxidative Rancidity

p. 1
2
Structure Properties (1)
Fats and oils glycerol fatty acids
Propane-1,2,3-triol
if the fatty acid part has many CC bonds
unsaturated
p. 2
3
Structure Properties (2)
forms fats (or oils) with glycerol
p. 3
4
p. 4
5
p. 5
6
Structure Properties (3)

• Unsaturated Oils usually have a lower melting
  point and exist as a liquid.
• Hydrogenation of some of the CC bonds converts
  to solid fats.
• e.g. Margarine

p. 6
7
Hydrolysis of Fats Oils

• Fats and oils are hydrolysed into carboxylic acid
  and glycerol in human body (acidic medium).

• In lab, hydrolysis can be carried out in alkaline
  medium more effectively, to give carboxylate and
  glycerol.

(saponification)
p. 7
8
Iodine Value (1)
? To measure the degree of unsaturation of a fat
or vegetable oil.
? It is defined as the number of grams of iodine
that reacts with 100 grams of fats/oils.
? Vegetable has a high iodine value than fats.
p. 8
9
Iodine Value (2)
higher iodine value ? higher degree of
unsaturation
Fats / Oils Fats / Oils Iodine values
Animal fats Butter 25-30
Animal fats Dripping (??) 35-65
Animal fats Lard (??) 45-65
Vegetable oils Coconut oil (???) 8-10
Soya oil (???) 80-140
Ground-nut oil (???) 85-105
Olive oil (???) 80-90
Almond oil (???) 90-110
Corn oil (???) 115-130
p. 9
10
Examples of Unsaturated Fatty Acid
p. 10
11
Hardening of Vegetable Oil

• Animal fats ---- usually saturated? regular
  packing

higher melting point, therefore solid state at rm
temp.
But the vegetable oil should not be completely
hydrogenated, otherwise, the solid will be too
hard!
catalytic (Ni) hydrogenation

• Vegetable oil ---- usually unsaturated?
  irregular packing (due to presence of
  cis-isomers)

lower melting point, therefore liquid state at rm
temp.
p. 11
12
Disadvantage of Animal Fats?
They contain larger amount of Cholesterol.
p. 12
13
Hydrolytic and OxidativeRancidity (??) of Fats
Oils
? Hydrolytic and Oxidative Reactions of
triglyceride molecules give out unpleasant
odour.
due to volatile and foul smelling RCHO Fatty
Acids
? Hydrolytic Rancidity occurs due to the presence
of moisture in the oils.
p. 13
14
Oxidative Rancidity (1)
? Oxidative Rancidity occurs under exposure to
air (oxygen)

• Very common for those with high iodine
  value? high degree of unsaturation --- more
  susceptible to oxidation!

? free radical mechanism!!
p. 14
15
Autoxidation
Oxidative Rancidity (2)
volatile aldehyde,ketones .
R-O-O-H
R-O-O?
hydroperoxide
hydroperoxide free radical
p. 15
16
Oxidative Rancidity (3)
? Oxidative Rancidity can be prevented by using
antioxidants (BHA or BHT)
R-O-O?
R-O-O-H
i.e. the hydroperoxide free radical is killed
by the H atom given by BHT ? chain reaction stops.
p. 16
17
Oxidative Rancidity (4)
? If the triglyceride molecules do not contain
any unsaturation carboxylic acid chain ..
? no hydroperoxide will be generated,and
therefore oxidative rancidity does not occur.
p. 17
18
HKALE .

• 1997 Vegetable oil (iodine value,
  hydrogenation and saponification)

• 1998 Animal Fats and Vegetable oil (iodine
  value, hardening, saponification and rancidity)

• 2001 Vegetable oil unsaturated oil
  (principle of anti-rancidity by BHT)

p. 18