Fats & OilsFats & OilsAL Chemistry
p. 1
Structure & Properties Hydrolysis of Fats & Oils Iodine Value Hardening of Vegetable Oil Hydrolytic & Oxidative Rancidity
Structure & Properties (1)Structure & Properties (1)
p. 2
Fats and oils = glycerol + fatty acids
Propane-1,2,3-triol
AL Chemistry
if the fatty acid part has many
C=C bonds
unsaturated
Structure & Properties (2)Structure & Properties (2)
p. 3
AL Chemistry
forms fats(or oils)
with glycerol
p. 4
p. 5
Structure & Properties (3)Structure & Properties (3)
p. 6
AL Chemistry
Unsaturated Oils usually have a lower melting point and exist as a liquid.
Hydrogenation of some of the C=C bonds converts to solid fats.
e.g. Margarine
Hydrolysis of Fats & OilsHydrolysis of Fats & Oils
p. 7
AL Chemistry
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) soap!
AL Chemistry
p. 8
Iodine Value (1)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. 9
Fats / Oils Iodine values
Animal fats Butter 25-30
Dripping ( 肉汁 ) 35-65
Lard ( 豬油 ) 45-65
Vegetable oils Coconut oil ( 椰子油 ) 8-10
Soya oil ( 大豆油 ) 80-140
Ground-nut oil ( 花生油 )
85-105
Olive oil ( 橄欖油 ) 80-90
Almond oil ( 杏仁油 ) 90-110
Corn oil ( 粟米油 ) 115-130
Iodine Value (2)Iodine Value (2)# higher iodine value higher degree of unsaturation
p. 10
Examples of Unsaturated Fatty Acid:Examples of Unsaturated Fatty Acid:
Chemical Names and Descriptions of some Common Fatty Acids
Common Name CarbonAtoms
DoubleBonds
Scientific Name Sources
Oleic Acid 18 1 9-octadecenoic acid olive oil
Linoleic Acid 18 2 9,12-octadecadienoic acid corn oil
-Linolenic Acid (GLA)
18 3 6,9,12-octadecatrienoic acid borage oil
Gadoleic Acid 20 1 9-eicosenoic acid fish oil
EPA 20 5 5,8,11,14,17-eicosapentaenoic acid fish oil
DHA 22 6 4,7,10,13,16,19-docosahexaenoic acid fish oil
p. 11
AL ChemistryHardening of Vegetable OilHardening of Vegetable Oil
Animal fats ---- usually saturated regular packing
higher melting point, therefore solid state at rm temp.
Vegetable oil ---- usually unsaturated irregular packing (due to presence of cis-isomers)
lower melting point, therefore liquid state at rm temp.
catalytic (Ni)hydrogenation
But the vegetable oil should not be completely hydrogenated, otherwise,
the solid will be too hard!
p. 12
Disadvantage of Animal Fats?
They contain larger amount of “Cholesterol”.
AL Chemistry
p. 13
Hydrolytic and OxidativeRancidity (酸敗 ) of Fats & Oils:
Hydrolytic and Oxidative Reactions of triglyceride molecules give out unpleasant odour…….
AL Chemistry
due to volatile and foul smelling RCHO & Fatty Acids
Hydrolytic Rancidity occurs due to the presence of moisture in the oils.
p. 14
AL Chemistry
Oxidative Rancidity occurs under exposure to air (oxygen)
Oxidative Rancidity (1) :
Very common for those with high iodine value► high degree of unsaturation
--- more susceptible to oxidation!
free radical mechanism!!
p. 15
AL Chemistry
C
H
H
C
H
C
H
C
H
H
O2 in the air
AutoxidationC
H
C
H
C
O
C
H
H
H
OH
segment of carboxylic acid in fat/oil hydroperoxide
Oxidative Rancidity (2) :
R-O-O-H[hydroperoxide]
R-O-O[hydroperoxide
free radical]
volatile aldehyde,
ketones ….
“Autoxidation”
p. 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.
AL Chemistry
p. 17
AL ChemistryOxidative 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. 18
AL ChemistryHKALE ….
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)