In this lesson, we will learn about plant oils – where they come from, how to extract
them, and
their generic structure.
Plant oils are obtained from plants.
These oils are found in all parts of a plant – seeds, nuts, fruit, leaves, flowers, bark,
and even
roots.
However, these oils must extracted before they can be consumed or used.
There are a few key methods to extract plant oils.
Mechanical extraction
Distillation
Steam distillation
Olive oil is obtained from olives by mechanical extraction.
This method is also known as cold pressing.
The olives are crushed and pressed to squeeze all the oil out.
In the past, these heavy machines were operated by humans.
Nowadays, most mechanical extraction is done in a factory by machines.
Coconut oil is also obtained using this method.
Note that both of these oils are essential cooking ingredients in certain parts of the
world.
Some plant oils, such as sunflower oil and soy oil, are obtained by distillation.
These oils are first dissolved in a solvent, and the solvent is removed by distillation.
Any impurities are also removed during this process.
This method is used for oils that are more difficult to extract from their respective
plants.
Steam distillation is used to extract floral oils, such as rose and lavender oils.
Steam is passed through the flower petals.
The oils are then able to evaporate.
Since the oil droplets are very small, they can form an emulsion with water.
The oil can then be separated by distillation.
We will now look at the general structure of plant oils.
The structure can be broken down into two parts:
The glycerol “head” which is hydrophilic, or water loving.
It is made of three carbons.
These three carbons are each attached to three fatty acid “tails” which are hydrophobic,
or
water-fearing.
The length of the tail can vary from oil to oil – it can be anywhere from 4 carbons
long to 28
carbons long.
These “tails” can be saturated or unsaturated.
The term saturated means that there are only C-C single bonds.
Saturated plant oils are solids at room temperature, and are also known as vegetable fats.
An example of a saturated plant oil is palm oil from oil palm trees.
The term unsaturated means that there are C=C double bonds somewhere within the structure
of the fatty acid tail.
A monounsaturated oil has only one C=C double bond.
A polyunsaturated oil has more than one C=C double bond.
Most unsaturated oils are liquids at room temperature.
These unsaturated oils can be hydrogenated through a process called hydrogenation.
This hardens the oil and is a key step in the production of margarine.
In the laboratory, one can differentiate between a saturated and unsaturated oil by testing
with
bromine water.
An unsaturated oil will decolourise bromine water, whereas a saturated oil would not.
Final Summary
In summary, plant oils can be obtained by mechanical extraction, distillation, or steam
distillation.
All plant oils have the same generic structure – a hydrophilic glycerol head, and three
hydrophobic fatty acid tails.
The fatty acid tail can be saturated if there are only C-C single bonds, or unsaturated
if there are
C=C double bonds present.