LIPIDS
© PDST Home Economics
Lipids
• The term lipids covers fats and oils
Fats= Solid at room temperature
Oils = Liquid at room temperature
Elemental Composition
Recall the elemental composition of
carbohydrates???
 Carbon (C)
 Hydrogen (H)
 Oxygen (O)
Note: These elements are found in different
proportions to carbohydrates.
Chemical Composition
• The formation of a Triglyceride
 A triglyceride is the chemical name given to a fat
 A triglyceride is formed when one glycerol molecule
joins with three fatty acids to produce a triglyceride
and water
 Water is eliminated (condensation reaction)
+
H20
+
H20
+
H20
+
+
+
Glycerol + 3 Fatty Acids =
Triglyceride + Water
Chemical Structure of Lipids
Chemical Structure of Lipids
• A Glycerol molecule has 3 Hydroxyl Groups (OH).
• Every fatty acid has a Carboxyl Group at the end.
• A Hydroxyl group from the Glycerol and a Hydrogen atom
from the end of the fatty acid break off and combine to
form water (H2O)
• As a result the fatty acid becomes bonded to the
glycerol.
• This happen for each of 3 fatty acids and 3 water
molecules are released.
Chemical Structure of Lipids
Fatty Acids
• There are many different Fatty Acids but all have same
basic structure.
• They are made of chains of carbon with a methyl group
at one end (CH3) and a carboxyl group at the other end
(COOH).
• What makes one fatty acid different from another is
the length of the carbon chain
• For example: butyric acid has 2 carbons in the carbon
chain whereas stearic acid has 18
Classification of Fatty Acids
• Fatty acids are long carbon chains with CH3 (methyl
group) at one end and COOH (carboxyl group) at the
other end.
• Fatty acids are classified into three groups
 Saturated fatty acids
 Monounsaturated fatty acids (mono = one)
 Polyunsaturated fatty acids (poly = many)
• The number of carbon atoms differs with each fatty
acid
Saturated Fatty Acids
• Each carbon atom is saturated with hydrogen
• There are no double bonds present between the
carbon atoms
• They are generally solid at room temperature
• They are generally from animal sources
• Examples: Butyric Acid in butter and Stearic Acid in
meat
Structure of Saturated Fatty
Acid
Monounsaturated Fatty Acid
• Each carbon atom is not saturated with hydrogen
• There is one double bond present
• These fatty acids are soft or liquid at room
temperature
• They originate from plant sources
• Example: oleic acid found in olive oil
Structure of
Monounsaturated Fatty Acid
Polyunsaturated fatty acid
• Each carbon atom is not saturated with hydrogen
• There is more than one double bond present
• These fatty acids are soft or liquid at room
temperature
• They originate from plant/marine sources
• Examples include linoleic acid in corn oil and linolenic
acid in vegetable oil
Structure of
Polyunsaturated Fatty Acid
Essential Fatty Acids
• Cannot be manufactured in the body and must be
supplied by the diet.
• These include linoelic acid found in corn oil, linolenic
acid found in vegetable oil, arachidonic acid found in
animal fat.
• Linoleic acid is the most important of these as
linolenic acid and arachidonic acid can be
manufactured from linoleic acid.
Functions of Essential Fatty Acids
(EFA’s)
• Build cell membranes
• Counteract the hardening effect of cholesterol in the
arteries
• Help prevent CHD
Cis and Trans Fatty Acids
• Cis and trans fatty acids are based on the position of
the hydrogen atoms at the double bond
Cis Fatty Acids
• Cis fatty acids occur when the hydrogen atoms are at
the same side of the double bond
H
H
C= C
Trans Fatty Acids
• Trans fatty acids occur when hydrogen atoms are on
the opposite side of the double bond
H
C=C
H
A Closer look at Trans fatty
Acids
• During cooking and processing Cis fatty acids are
converted into trans fatty acids e.g. through the
addition of hydrogen during margarine manufacturing
(hydrogenation)
• Trans fatty acids are thought to increase the risk of
coronary heart disease (CHD), in particular trans
fatty acids that are produced synthetically
• Tests have shown that they raise the level of low
density lipoproteins (LDL) or bad cholesterol and
reduce high density lipoproteins (HDL) or good
cholesterol
Effects of cholesterol on the artery
Sources of Trans fatty acids
Omega 3 Fatty Acids
• These are polyunsaturated fatty acids
• Omega 3 relates to the positioning of the double bond
• The double bond is between the 3rd and 4th carbon
atom counting from the methyl end.
• Omega 3 fatty acids are known as EPA
(eicosapentaenoic acids) and DHA (docoshexaenoic
acids)
Omega 3 Fatty Acids
Sources: Oily Fish – Salmon, herring, mackerel,
nuts, seeds, soya beans, supplements
Benefits: Reduced risk of heart attack, strokes,
circulatory diseases and formation of blood clots.
Increase HDL cholesterol levels. It is also
associated with healthy brain activity.
Properties of Lipids
1. Solubility
• Lipids are insoluble in water
• Lipids are soluble in solvents eg.
Ether & benzene
2. Plasticity
• A combination of saturated &
unsaturated fatty acids allows
for shape & structure of the
lipid
• This is useful in pastry making,
e.g. Margarine is used in the
creaming method
3. Hydrogenation
• Hydrogenation occurs when
hydrogen is forced through the
double bond of unsaturated
fatty acids in the presence of a
nickel catalyst
• This property is evident in the
production of margarine
• A catalyst is a substance that
speeds up or slows down a
reaction without itself
changing
Hydrogenation continued..
H H
- C = C-
H
H
+ H2 - - C = C -
H
H
Properties of lipids cont...
4. Affected by heat
• There are varying temperatures that affect lipids (Fats &
oils)
Melting Point
•Solid fats melt when
heated
•FATS: 30-40˚C
Smoke Point
Flash Point
•Lipids begin to
decompose to gylcerol
& 3 fatty acids
•A blue haze emerges
•An acrid-smelling
compound known as
acrolein is present
•FATS: 200˚C
•OILS: 250˚C
•The decomposition of
the lipids continues
•Lipids spontaneously
burst into flames
•FATS: 310˚C
•OILS: 325˚C
5. Rancidity
• This is the term used to describe lipids when they
‘go off’
• There are two types of rancidity: these are
oxidative & hydrolytic
• To prevent rancidity, store food correctly & use an
anti-oxidant
• Anti-oxidants occur naturally in vitamins A, C & E
and artifically in BHA & BHT
Oxidative
Hydrolytic
Rancidity
Cont...
•This
form of rancidity occurs
•This form of rancidity occurs
when oxygen is forced through
the double bond of an
unsaturated fatty acid. It is the
most common form of rancidity
H
H
H H
-- C
C -- + O2
-- C—C--
O O
•Eg. Oil solidifying on a pan
when enzymes & bacteria react
with the lipid
•This occurs most commonly in
freezers when enzymes are not
destroyed
•It results in the triglycerides
breaking down – flavour is
altered
6. Emulsions
• There are two types of emulsions: oil in water & water
in oil
• When two immiscible liquids are forced together, an
emulsion is formed
1. A temporary emulsion occurs when oil and vinegar are
forced together, e.g. French dressing – this is caused
by shaking & will seperate on standing
2. A permanent emulsion occurs when oil & water are
forced together in the presence of an emulsifier, eg.
Mayonnaise (oil + water + emulsifier - lecithin in egg
yolk) = Emulsion
• An emulsifier has two parts: a water -loving head
(hydrophilic) & a water-hating tail (hydrophobic)
• Hydro: Water
Philic: Love
Phobic: Hate
Vinegar
Working Principle of an
Emulsifier
Oil
Hydrophobic
tail
Hydrophilic
head
• The hydrophilic head attaches to water, while the
hydrophobic tail attaches to the oil
• The hydrophilic head attaches itself to the water
molecule
• The hydrophobic tail attaches itself to the oil
component of the emulsion
OIL
WATER
• Stabilisers are used to maintain an emulsion, eg. In
ice cream
• An example of a stabiliser used in ice cream is
alginates (E400)
Vinegar
Oil
Stabiliser
Digestion of Lipids
Liver: Produces Bile, contains
salts
Bile Salts break lipids down into
emulsified fats
Pancreas: Pancreatic Juice
contains pancreatic lipase. This
lipase breaks lipids into 1 glycerol
molecule and 3 fatty acids
Illeum (small intestine): Intestinal juices
contain intestinal lipase. This lipase
continues breakdown of lipids into 1
glycerol molecule and 3 fatty acids
Organ/
Gland
Secretion
Enzyme
Substrate
By
Product
Liver
Bile
Bile
Salts
Lipids
Emulsified
fats
Pancreas
Pancreatic
juices
Pancreatic
lipase
Lipids
Glycerol +
3 fatty
acids
Illeum
Intestinal Juice
Intestinal
Lipase
Lipids
Glycerol +
3 fatty
acids
Absorption of Lipids
• When digested the lipids (glycerol + 3 fatty acids)
can be absorbed
• Absorption takes place in the lacteals in the villi of
the small intestine
Absorption of Lipids
• Digested lipids are carried via the lymph system to
the bloodstream at the subclavian vein in the neck.
Utilisation of Lipids
Lipids are oxidised in the liver and muscles to
1. Produce heat and energy
2. Form cell membranes
Excess lipids are stored in the adipose tissue
underneath the skin. This
1. Insulates the body
2. Acts as an energy reserve
3. Protects delicate organs