2. CHEMICALS THAT MAKE UP FATS AND ITS
FUNCTIONS
Carbon
Hydrogen
Oxygen
Functions
Energy – 1g of pure fat provides 37KJ (9kcal)
Formation of Adipose tissue – used as an Energy
reserve, Insulates and Protection
Source of essential fatty acids
Fat soluble vitamins: A,D,E,K
3. SOURCES OF FAT
Meat and Fish
Confectionary
Processed Foods
Butter, Margarine, Lard
Egg Yolk (Contains Cholesterol)
Uses of Food Production
Creaming and Aerating
Frying
Shortening
4. CHEMICAL STRUCTURE
Fat belongs to a group of substances called Esters.
Formed by the reaction between an alcohol and
organic acid – known as fatty acids
Glycerol is a complex alcohol because it has 3
hydroxyl groups therefore known as a Trihydric
Alcohol.
5. CHEMICAL STRUCTURE CONT.
Ester formed is a triglyceride.
If all 3 fatty acids are the same, then Simple
Triglyceride is formed.
If fatty acids are different then they are called Mixed
Triglyceride.
Fatty acid Formula = R- COOH (‘R’ represents any
acid).
6. CIS AND TRANS FATTY ACIDS
CIS
2 hydrogen atoms on the same side of a double
bond.
Trans
Hydrogen atoms on geometrically opposite sides of
the double bond.
7. SATURATED FATS
Occur when each carbon atom is attached to the
surrounding atoms by a single bond.
The carbon atoms are completely saturated with
hydrogen atoms.
Saturated fats have a melting point at about room
temperature and are therefore usually hard – Could
lead to heart disease and high cholesterol.
9. UNSATURATED FATS
Occur when some of the carbon atoms are joined to
the surrounding hydrogen atoms by a double bond.
Monounsaturated fats have one double bond.
Polyunsaturated fats have more than one double
bond.
Unsaturated fats are mainly oils and have a melting
point at below room temperature.
Saturated Fatty Acid Monounsaturated Polyunsaturated
Fatty Acid Fatty Acid
Palmatic Acid Oleic Acid Linoleic Acid
Stearic Acid Linolenic Acid
11. PROPERTIES OF FATS AND OILS
Solubility
Fats and oils are insoluble in water.
However, in the presence of a suitable substance
known as an emulsifying agent, it’s possible to form
a stable mixture of fat and water Emulsion.
The Emulsion may be a Fat – in – Water emulsion
e.g. Milk
Or a Water – in – Fat emulsion e.g. Butter
Fats and oils are soluble in organic solvents such as
petrol and carbon tetrachloride.
Solvents of this type can be used to remove grease
and stains from clothing.
12. PROPERTIES OF FATS AND OILS
Plasticity
Fats do not melt at fixed temperatures, but over a
range of temperatures.
This is because fats are mixtures of triglycerides
(contain 3 different fatty acids), all with different
melting points.
Some of the fatty acids forming the triglyceride will
stay solid for longer than others.
This feature gives fat its plasticity that makes some
fats spreadable.
E.g. Margarine – Has a wide range of plasticity and
will spread from the fridge whereas most animal fat
will have narrow plasticity and will not spread easily.
13. PROPERTIES OF FATS AND OILS
Effect of Heat
Oils and fats transfer heat well to foods being cooked but
will eventually breakdown.
Heating causes the triglycerides to decompose.
Melting Point
Fats melt when heated. Since fats are mixtures of
triglycerides they do not have a distinct melting point but
melt over a range of temperatures.
Temperature when melting occurs is known as the Slip
Point.
Most fats melt at temperatures of 30 /40 C
Melting point for oil is below normal air temperature – The
more double bonds, the lower the air temperature.
14. PROPERTIES OF FATS AND OILS
Smoke Point
When a fat or oil is heated to a certain temperature it starts
to decompose, producing a blue haze or smoke.
Most fats and oils start to smoke at 200 C
Smoke Point for lard = 185 C
Corn Oil = 232 C
In general, vegetable oils have a higher temperature than
animal fats.
Smoke is useful to measure when assessing the suitability
of a fat or oil for frying purposes.
Repeated heating of a fat or oil will reduce the smoke
point.
15. PROPERTIES OF FATS AND OILS
Saponification
Some triglycerides react with alkalis to form soap and a
glycerol.
Hydrogenation
Some oils are so unsaturated in the natural state that they
need to be treated to make them useful in food.
Hydrogenation is used to add hydrogen to the oil to break
the double bonds. This makes the resulting fat more
saturated and harder.
It is achieved by heating the oil in a large sealed vessel
under pressure.
Hydrogenated fat makes TRANS fats which increases
likelihood of cancer and free radicals in the body.
16. RANCIDITY
Used to describe the spoilage of fats and oils. Fat
which is rancid will have an unpleasant smell and
flavour.
Oxidative Rancidity
Reaction between unsaturated triglycerides and
oxygen from the air.
Oxygen molecules join across the double bond of the
triglyceride molecule and a variety of compounds
are formed e.g. Aldehydes and Ketones – gives the
unpleasant rancid taste.
Reaction is accelerated by heat, light and traces of
metals e.g. copper/ iron.
17. RANCIDITY CONT…
Hydrolytic Rancidity
Enzymes known as lipase hydrolyse fats, breaking
them down into glycerol and fatty acids.
Equation
Fat + Water Glycerol + Fatty Acids
Short Chains = More rancid
18. HOW TO STOP RANCIDITY
Keep fats free from oxygen and air.
Keep metals and light away from fats.
Do not store oil in iron containers use glass!
Salt speeds up rancidity.
Sugar slows down rancidity.
Anti-oxidants can be used to slow rancidity.
19. USES IN FOOD PREPARATION
Frying
Fast cooking method – bad for health as it increases fat
content, but tastes good.
Frying occurs at 180 C
Shortening
It’s an effect that fat has on a product – increases the
crumbly texture of foods.
Stops the formation of effects of gluten.
Fat coats the flour preventing water making the flour
stretchy.
Creaming and Aerating
Adding air bubbles
Lighter colour
Increases volume – it rises due to trapped air.
20. PRODUCTION OF FATS AND OILS
Vegetable Oils
70% of all oils in the world are vegetable oils
It increases polyunsaturated fatty acids (PUFA).
Margarine
An emulsion of water and fat.
The vegetable fat being used is first hydrogenated to
give it some hardness (plasticity), and is then
blended with skimmed sour milk, salt, colouring and
Vitamins A and D (added by law).
Hard margarines are more hydrogenated then soft
ones.
21. PRODUCTION OF FATS AND OILS
Spreads and Low Fat Spreads
Less then 80% fat
Increase water content – not suitable for cooking.
Cooking fats and Shortening
First produced in USA as a substitute for lard and are
pure fat products rather than emulsions.
Blended with fish oils, animal fats and are
hydrogenated.
These fats are called High Ratio Fats and are
designed for recipes e.g. Muffins
22. PROPERTIES OF FATS AND OILS CONT…
Lard
Extracted from pigs via heating OR ‘rendering’.
Almost 100% fat
Butter
Churning of pasteurised cream, this causes the cream to
become more viscous forming a solid butter.
Colour and salt is added to butter and is mixed for desired
consistency.
Suet
Fat from around the kidneys of animals.
Sold in the form of shredded suet and used in Christmas
puddings and Suet puddings.
23. CHOLESTEROL
A waxy white substance found in fats, particularly
hard animal fats which can block arteries and be
one of the causes of heart disease.
Cholesterol is carried around the body by specific
proteins which come together to form a lipid –
protein complexes called Lipoproteins.
High-density Lipoproteins (HDL) is beneficial because
it transports cholesterol from places where there is
too much, to the liver where it is disposed of.
Low-density Lipoproteins (LDL) can lead to deposits
in the arteries (plaque) which causes narrowing.
24. ESSENTIAL FATTY ACIDS
Essential means that these substances cannot be made in
the body so must be gained from food sources.
Two main types of essential fatty acids (EFA) are:
Polyunsaturated Fatty Acids (PUFA) – Linolenic and
Linoleic acid.
Longer chain fatty acids: Arachidonic acid, EPA and DHA
(these can be made in the body to a limited extent by
linoleic acid and alpha linolenic acid)
EFAs are needed for:
The maintenance of cell membranes.
Hormone like substances called Eicosanoids
(prostaglandins etc) which are involved in clotting blood.
