Plant Oil Chapter#14

 

Plant Oil

Chapter#14

Oils in plants:

Like animals, plants also store excess energy they take in as chemical energy in fats. The fats in plants are often liquids at 20^oC so we call them oils.

Extracting the oil from plants:

In order to get the oil from a plant, we have to break open its cells to release it. There are two main ways to break down the cell walls:

• Pressing (applying pressure)
• Distillation (heat using steam)

Then water and other impurities are removed.

Pressing:

´  In this method we squash the plant material. Then we collect the liquid. The oil and the water-based solutions are immiscible.

´  They do not dissolve in each other and will separate out into two layers.

´  Then the oil and water are separated by centrifuging (spinning the mixture at high speeds) or just by decanting (pouring off).

Distillation:

To extract plant oils we can either:

´  Boil up the plant material with water, or

´  Pass steam through the plant material.

 

Emulsions:

An emulsion is a finely dispersed mixture of two or more liquids that do not dissolve in each other.

Emulsifiers:

Salad cream also contains oil and water. Salad cream has egg yolk added. This keeps the oil droplets mixed with the water. It stops the oil and water separating out into layers.

A substance that does this is called an emulsifier.

Margarines:

Margarines are made from plant oils. Sunflower oil is a popular choice for margarine manufacturers.

Hardening plant oils:

The reaction takes place at about 60^oC with a nickel catalyst:

Plant oil  +  hydrogen  à  margarine (less                                                                                                                                                                                                               unsaturated than the oil)

 

Detergents:

Many detergents are made from the products of crude oil. Washing-up liquid is an example.

Detergents are substances which help the cleaning action of water.

Water is good at dissolving many things. However, it cannot dissolve oil or grease. This is where detergents help. They act as emulsifiers. They remove grease and keep it dispersed in water.

Soaps:

We can summaries the reaction as:

Oil/fat  +  sodium hydroxide  à  soap  +  glycerol

Making soap is called saponification.

Soapless detergent:

Soaps are detergents. Traditionally, they are made from animal fats and plant oils.

Using soap in areas with hard water causes ‘scum’ to form.

Soapless detergents from crude oil do not have this problem. Soapless detergents do not make ‘scum’ in hard water.

Treating oil spills:

Crude oil is transported in giant oil tankers. If these ships have an accident, the crude oil can escape.

It floats on top of the sea, forming an oil slick. Soapless detergents are used to clean up the mess.

The detergents breaks up the slick. Then the oil is spread out by the action of the waves.

                        Class Work

Colourings :

When we process foods much of the natural colour is lost. The food does not look appetising. So food chemists have searched for substances to put the colour back into processed food.

Preservatives and anti-oxidants:

Fresh foods soon ‘go off’ as they are attacked by bacteria or oxygen in the air. For example, fats in food are oxidized to acids, making it rancid.

However, preservatives and anti-oxidants protect the food

                                                                                          Class work               

Emulsifiers and stabilisers:

These help fats and oils to mix with water.

For example, a Caramel cake bar contains emulsifiers E471 and E475.

Disadvantages of food additives:

Butylated hydroxylanisole (E320) is another controversial compound.

It was banned in Japan as early as 1958 and experts recommended its ban in the UK.

E954 is an artificial sweetener. It was banned in the USA.

 

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