Naturally Occurring Molecules from plants
Fats, Oils and Margarine
Natural vegetable oils and animal fats
are important raw materials for the chemical industry wide ranging applications and uses e.g. soaps, detergents, cosmetics,
lubricants, paints, many food industry products. It is possible that
in future vegetable oils could be an important renewable and
sustainable alternative to some of the products we derive from crude
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OILS and FATS - molecular structure
Oils and Fats
are an important way of storing chemical energy in living
systems and are also a source of essential long–chain fatty acids.
Plant oils and animal fats have
a high energy density (higher than carbohydrates) and be easily stored in
living organisms until they are needed to supply extra energy to power the
chemistry of life.
If we take in more calorific
food that we need e.g. excess carbohydrate or 'fatty food', then that excess
energy supply is converted to fat and stored for future use, but, if it
isn't used up, then obviously you will put on weight.
- Fats and oils are esters formed from
long chain fatty acids and the 'triol' alcohol glycerol
which has three C–O–H groups.
- Glycerol is the alcohol plants and animals use to make
oils and fats which are esters we use in food and soaps.
- Animals and plants combine glycerol and long
chain fatty acids to make triglyceride esters – fats from animals and oils
Most of them are esters of
the tri–alcohol ('triol') glycerol (systematic name
propane–1,2,3–triol, but that can wait until Advanced A Level).
The carboxylic acids which
combine with the glycerol are described as 'long–chain fatty acids'.
The resulting ester is called a
'triester' or 'triglyceride' and they are the major components in animal
fat, vegetable oils, and processed fats like margarine etc..
The 'long–chain fatty acids'
can be saturated, with NO C=C double bonds, and so forming saturated oils
or fats (1st diagram below of the triglyceride formed from palmitic
The 'long–chain fatty acids'
can be unsaturated, with one or more C=C double bonds, and so forming
oils or fats (2nd diagram below of the triglyceride formed from oleic
If there is just one
C=C double bond in the fatty acid chain, it is known as a
monounsaturated oil or fat (upper diagram).
If there are at least
two C=C double bonds in the fatty acid chain it is called a
polyunsaturated oil or fat exemplified by the polyunsaturated fatty
acid chain, with three carbon = carbon double bonds of the unsaturation,
in the lower diagram.
Plant oils are mainly
unsaturated fats with one or more carbon = carbon double bonds in the
fatty acid chain and they are usually thick (viscous) liquid oils at
room temperature. That's why plant oils are hydrogenated, adding
hydrogen to the double bonds, to make them less unsaturated and raise
the melting point to produce spreads like margarine.
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Oil and Fat Structure
and reaction with bromine:
issues dealt with further down)
Most oils and fats have quite long
fatty acid chain molecules in their molecular structure, which can be ...
Saturated, with no
double carbon = carbon bonds, so no atoms can be added to the molecule,
in this context they are referred to as saturated fat molecules.
Unsaturated, with one
or more carbon = carbon double bonds in the three fatty acid parts of
the molecule. In this context these molecules are referred to as
monounsaturated or polyunsaturated vegetable oils.
Unsaturated oils will
decolourise bromine water, a simple test for unsaturation.
This is because bromine
atoms can add across the double bonds like any
Ignoring the rest of the
molecule, the reaction in the unsaturated part of the oil/fat molecule
Although much shorter than
polymer molecules, oils and fats have the same ester linkages as perfume
molecules and Terylene
plastic, but with different units,
food for thought!
They are not as big as polymer molecules, but a lot bigger than a single
petrol or a simple sugar molecule.
There can be 1 to 3 different saturated or
unsaturated fatty acid components, so lots of variation possible in structure
of the oil or fat.
Monounsaturated fats have one C=C
double bond in the fatty acid chains, polyunsaturated fats usually have at least
two C=C bonds in their molecular structure.
For the same molecular size in terms of
carbon number, unsaturated fats have slightly lower intermolecular
forces because the C=C double bond produces a kink in the carbon
chain and they can't pack as closely together as the saturated
However, this means these unsaturated
oils are not as conveniently 'spreadable' as 'butter'.
To overcome this problem, 'margarine'
was invented in which the runny vegetable oil is 'hardened'
by hydrogenation to produce a higher melting spreadable solid.
The melting point is
still low, but not to low to remain liquid at room temperature ie a margarine is a soft solid at room
temperature and doesn't go too hard in the refrigerator and spreads
So, large quantities
of vegetable oils are hydrogenated for the food industry to
convert them from runny oils into low melting soft solids that
spread on bread etc. easily.
The vegetable oils are reacted with
hydrogen gas at 60oC using
a nickel catalyst (Ni).
These are called
and have higher melting point than unsaturated vegetable
oils, so they are a low melting solid at room temperature rather than the sticky–syrupy vegetable oil you
might use is cooking and salad dressings.
This reaction adds hydrogen
atoms to the double bonds making a more saturated and more
'spreadable' higher melting soft solid fat that we call 'margarine'.
no double bond and unsaturated means double bond in this context.
The reaction for any
carbon = carbon double bond,
+ H2 == Ni ==> –CH2–CH2–
converting an unsaturated part of the molecule to a saturated
This type of reaction is
called hydrogenation – quite literally – addition of
represents the unsaturated part of the hydrocarbon chain parts
in the oil molecule.
While the margarine
is still liquid, the expensive nickel catalyst can be recovered
from the margarine by filtration and reused.
On cooling down the
solid margarine is formed, but still soft enough to spread
polyunsaturated vegetable oils are hydrogenated to make
The diagram above
illustrates in a simplified way the hydrogenation of a
monounsaturated fat (one double bond per fatty acid chain) to a
fully saturated flat. Note that one hydrogen molecule is added
to each double bond giving the balanced equation for
hydrogenating vegetable oils to margarine.
In the case of
margarine, made from polyunsaturated vegetable oil, the oil is
only partially hydrogenated, thus reducing the number of C=C
double bonds in the molecule, BUT not making a saturated fat and
still raising the melting point above room temperature. If it
was completely saturated it would be too hard to spread.
BUT it does mean that it is
more like animal fat now but various blendes have been developed to
suit your dietary needs or desires!
The hydrogenated oils
are used as spreads and general baking like cakes, bread and
Technically, margarine is only partially hydrogenated because fully saturated
fats would be too hard and difficult to spread, but if a high % of
the double bonds are hydrogenated, the texture of the margarine is a
bit like butter and the 'buttery effect' appeals to many consumers.
Instead of butter,
margarine and other partially hydrogenated vegetable oils are used
in processed foods because they are cheaper and gives food products
a longer shelf–life.
other 'spreadable' fats based on vegetable oils are quite a
mixture of molecules known as an
A typical mixture might be
fats (triglycerides with almost no double bonds in the hydrocarbon
monounsaturates in which there is about one double bond per
polyunsaturates which have more than one double bond per molecule.
In terms of
melting points, the order is saturates > monounsaturates >
and water ('salt' solution'), small amounts of protein and
carbohydrate and whey or buttermilk are added to the fat/oil mixture
together with an emulsifier.
To stop the salt
solution separating out from the 'oily' fats an
added, which keeps the aqueous salt solution dispersed in the
fats or they would separate into two layers and affect the look
Incidentally the emulsifiers may be mono– or di–glycerides of
fatty acids, that is molecules like the vegetable oils but only 1 or
2 fatty acids attached to the glycerol rather than 3, which leaves 2
or 1 –OH hydroxy groups on the glyceride molecule.
These emulsifying molecules have the
bifunctional structure (see diagrams D and E1 below) because through the action of intermolecular
forces they bind with both fats (via hydrocarbon chain,
'water hating' hydrophobic end of molecule) and bind with water
too (via hydroxy group OH, the 'water loving' hydrophilic
end of molecule). This double interaction with the oil/fat holds the emulsion or dispersion together and
stopping the formation of two layers (aqueous and oil/fat).
In margarine or
butter there will be far more of the oil/fat than water, but the
diagram is just meant to give an idea of how an emulsion is
stabilised. The diagram below is better representation of
margarine with its emulsifying agent which is often
monoglyceride or diglyceride esters of fatty acids. The hydrocarbon tails
sticking out from the minute water globules, make the water
compatible with the hydrogenated vegetable oils.
A water oil emulsion
For a more general and wider description of emulsions
Aqueous solution chemistry
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Examples of food labelling on
Spread 1 is made from vegetable fats and olive
oil. The oil/fat analysis shows it is a mixture of saturates,
monounsaturates and polyunsaturates. The total oil/fat is 59% by mass,
adding all the rest up means there is about 38% water in this oil in water
The labelling on this fat spread made from
vegetable oil is packed with nutritional information. Apart from the oil/fat
composition in spread 2 (assume similar in spread1) there added vitamins, salt, water, emulsifiers, flavourings etc.
etc. In spread 2 there is, by mass, 14% saturated fats, 15.9%
monounsaturated fats and 25.5% polyunsaturated fats.
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Animal fats, vegetable oils and
Since fats and oils are important to our
diet, there is the ever present danger of over–consumption (speaking as
someone who loves chips and spicy crisps!).
So there are health and
social, as well as 'molecular' issues to address!
Vegetable oils are an important
source of energy and even vitamins like vitamin E in seed
Vegetable oils contain essential fatty acids which are bodies need for certain metabolic
So we need both oils and fats as sources of
important essential fatty acids and energy.
We need both saturated and unsaturated
fats or oils.
Animal fats tend to be
saturated molecules and vegetable oils tend to be unsaturated
The main sources of saturated fats
are from meat and dairy products e.g. 'dripping', butter, lard from
pork fat, blubber from whale fat, cod liver oil from fish, ghee
The main sources of unsaturated fats
are plant oils e.g. olive oil, walnut oil.
Animal fats are usually
solids at room temperature, though with low melting points, but
vegetable oils/fats tend to be liquids.
It is recommended that we do not
overdo the fat intake but we do need both saturated and unsaturated
Whatever fat or oil you use
in cooking – food preparation, you are significantly increasing your
calorie intake from these energy rich molecules and it doesn't matter
the oil/fat is polyunsaturated, partially hydrogenated or fully
In general unsaturated fats
are more healthy to consume than saturated fats and reduce the level of
cholesterol in your bloodstream.
However, too much saturated fat
raises cholesterol levels and is not too good for the heart –
increased blood pressure and poor blood circulation from blocked
arteries and heart disease can result from a diet high in saturated
animal fats – but you do need some and eating saturated fats in
moderation shouldn't be a problem.
Natural highly unsaturated
vegetable oils like walnut oil, olive oil, sunflower oil etc. do tend to
reduce cholesterol levels.
The consumption of trans
fats, and animal fats in general, increases the risk of coronary heart disease by raising levels
of LDL cholesterol and lowering levels of 'good' HDL cholesterol.
However even partially
hydrogenated vegetable oils contain 'trans–fats' which are not supposed to
be good for you, because they also tend to increase 'bad' cholesterol levels
and decrease 'good' cholesterol levels in your blood stream, and
therefore the risk of heart disease, so, eating lots of food containing
margarine etc. is not good for you!
of diet, food additives and cooking chemistry
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molecular structure, how they are made and how they work