1. LIPIDS
© PDST Home Economics

2. Lipids The term lipids covers fats and oils
Fats= Solid at room temperature
Oils = Liquid at room temperature

3. Elemental Composition
Recall the elemental composition of
carbohydrates???
Carbon (C)
Hydrogen (H)
Oxygen (O)
Note: These elements are found in different proportions to carbohydrates.

4. 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)

5. Glycerol + 3 Fatty Acids = Triglyceride + Water
H20 +
Glycerol + 3 Fatty Acids = Triglyceride + Water
Chemical Structure of Lipids

6. 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.

7. Chemical Structure of Lipids

8. 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

9. 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

10. 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

11. Structure of Saturated Fatty Acid

12. 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

13. Structure of Monounsaturated Fatty Acid

14. 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

15. Structure of Polyunsaturated Fatty Acid

16. 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.

17. Functions of Essential Fatty Acids (EFA’s)
Build cell membranes
Counteract the hardening effect of cholesterol in the arteries
Help prevent CHD

18. Cis and Trans Fatty Acids
Cis and trans fatty acids are based on the position of the hydrogen atoms at the double bond

19. Cis Fatty Acids
Cis fatty acids occur when the hydrogen atoms are at the same side of the double bond
H H
C = C

20. Trans Fatty Acids
Trans fatty acids occur when hydrogen atoms are on the opposite side of the double bond H
C = C H

21. 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

22. Effects of cholesterol on the artery

23. Sources of Trans fatty acids

24. 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)

25. 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.

26. Properties of Lipids 1. Solubility Lipids are insoluble in water
Lipids are soluble in solvents eg. Ether & benzene
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

27. Hydrogenation continued..
H H H H - C = C- + H2 - - C = C - H H

28. Properties of lipids cont...
4. Affected by heat
There are varying temperatures that affect lipids (Fats & oils)
Melting Point
Smoke Point
Flash Point
Solid fats melt when heated
FATS: 30-40˚C
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

29. 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

30. Rancidity Cont... Oxidative Hydrolytic
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 O C—C--
O O
Eg. Oil solidifying on a pan
This form of rancidity occurs 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
Rancidity Cont...

31. Emulsions
There are two types of emulsions: oil in water & water in oil
When two immiscible liquids are forced together, an emulsion is formed
A temporary emulsion occurs when oil and vinegar are forced together, e.g. French dressing – this is caused by shaking & will seperate on standing
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

32. Working Principle of an Emulsifier
Vinegar Oil Hydrophobic Hydrophilic tail head
The hydrophilic head attaches to water, while the hydrophobic tail attaches to the oil

33. 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

34. 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

35. Organ/ Gland Secretion Enzyme Substrate By Product Liver Bile Salts
Lipids
Emulsified fats
Pancreas
Pancreatic juices
Pancreatic lipase
Glycerol + 3 fatty acids
Illeum
Intestinal Juice
Intestinal Lipase

36. 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

38. Absorption of Lipids
Digested lipids are carried via the lymph system to the bloodstream at the subclavian vein in the neck.

39. Utilisation of Lipids Lipids are oxidised in the liver and muscles to
Produce heat and energy
Form cell membranes
Excess lipids are stored in the adipose tissue underneath the skin. This
Insulates the body
Acts as an energy reserve
Protects delicate organs