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Plant oils

What you need to know

Reflections and Exam tips


Plant oils and their uses

Many plants produce useful oils that can be converted into consumer products including processed foods. Some fruits, seeds and nuts are rich in oils that can be extracted.

There are two ways to extract the oils:

  1. Pressing - The plant material is crushed and the oil removed by pressing.
  2. Distillation - The oil is dissolved in a solvent such as hexane and then the solvent is distilled off leaving the oil behind.

Water and other impurities are removed.

Vegetable oils are unsaturated (due to their C=C double bonds) and are referred to as polyunsaturated fats. Unsaturated fats can be detected by adding bromine water. Bromine water turns from orange-brown to colourless when it reacts with unsaturated fats.

Cooking with Vegetable oils

Vegetable oils are important foods and fuels because they provide a lot of energy. They also provide nutrients such essential vitamins e.g. olive oil contains vitamin E.

Vegetable oils have higher boiling points than water and so can be used to cook foods at higher temperatures than by boiling.

This produces quicker cooking and different flavours, but it  increases the energy that the food produces when it is eaten. Unsaturated fats (olive oil) are healthier than saturated fats (butter), as saturated fats block up arteries causing heart disease.


Unsaturated liquid oils turned to solids (margarine) by partially saturating the oil (removing the double bonds to make single bonds). Hydrogenation increases the melting point of the vegetable oil. Hardening makes the vegetable oil solid at room temperature so they are spreadable. The oil is heated at very high temperature (60°C) in the presence of nickel catalyst.


Oils and fats do not dissolve in water they are immiscible. Oils can be used to produce emulsions which are tiny droplets of oil suspended in water.

The emulsions are thicker than oil or water and have many uses that depend on their special properties. Emulsions provide better texture, coating ability and appearance, which are useful in:

  1. salad dressings
  2. ice creams
  3. cosmetics
  4. paints

In order to prevent water and oil separating an emulsifier is added. Emulsifiers are used to make emulsions stable. They have hydrophilic (water loving) heads and hydrophobic (water hating) tails.

Emulsifiers make oil and fat more edible in foods by thickening foods making it creamier and more palatable. However, unsaturated fats can reduce the amount of ‘bad’ cholesterol in blood caused by foods high in saturated fats, therefore reducing the risk of heart disease.

Describe where vegetable oils come from.

Give uses for vegetable oils.

Explain what happens when oil mixes with water.

Compare saturated and un-saturated vegetable oils.