Getting Oil from plants
Many plants produce fruit,seeds and nuts that are rich in oils. The oil can be extracted from plant materials by pressing (crushing)then or distillation. These processes remove the water and other impurities from the plant material.
Vegtable oils are important foods. These oils provide you with nutrients and energy. Vegetable oils can also be used as a fuel in converted vehicles, instead of petrol or diesel.
Vegetable oils contain double carbon-carbon bonds, so they are unsaturated. They can be detected using bromine water. Unsaturated fats (oils) delcolourise bromine water. Vegetable oils are used in cooking because they have a higher boiling point than water so can be used to cook foods at higher temperatures. This means that food can be cooked mre quickly and a different is added to food.
Cooking useing vegetable oil also increase the energy that food releases when it's eaten. Cooking with oils higher in unsaturated fats is believed to be healthier than cooking with saturated fats.
Use of Vegetable Oils in Cooking
Generally, the more double carbon-carbon bonds there are in a substance, the lower it's melting point. So, unstaurated fats (oils) tend to have melting points below room temperature.
The melting point of an oil can be raised above room temperature by removing some or all of it's carbon-carbon bonds. This harderns the oil into a solid fat, for example margarine, which can be spread on bread or used for making cakes and pastries.
This hardening process is called hydrogenation.
1. The unstaurated fat (oil) is heated with hydrogen at about 60oC, in the presence of a nickel catalyst.
2. A reaction takes place that removes the double carbon-carbon bonds to produce a saturated fat (hydrogenated oil). Removing more double bonds makes the saturated fat harder.
Unsaturated fat + hyrdrogen ----> Saturated Fat
Oils don't dissolve in water, but an oil can be mixed with water to produce an emulsion.
Emulsions are thicker than oil or water and have a ...
- better texture
- better apperance
- better coating ability
Emulsions have many uses, for example in ...
- salad dressings
- ice cream
Hydrophobic and Hydrophilic Properties of Emulsifi
An emulsifier is a substance that helps to stabilise an emulsion.
Emulsifier molescules have a...
- Hydrophilic (water loving) head that mixes with the water molecules.
- Hyrdophobic (water hating ) tail that mixes with oil molecules
This allows water and oils to mix.