Why are vegetable oils useful in cooking?
They have high boiling points, higher than water, so food can be cooked at higher temperatures therefore faster.
Veg oil also changes flavour, colour and texture of food.
Vegetable oils are unsaturated. How can they be made more saturated?
Describe the process.
Vegetable oils mean be hardened/hydrogenated by reacting the, with hydrogen at 60oC with a nickel catalyst.
This makes them solids at room temperature and suitable for spreading.
How can vegetable oils be extracted and why are they useful?
Veg oils can be extracted from:
Pressing or distillation.
Veg oils provide nutrients and lots of energy. Can be used to make biofuels.
What do emulsifiers do and why do we need them?
Oil and water do not mix.
To mix them we need an emulsifier, which will keep the oil and water together.
Milk is an oil-in-water emulsion.
What does 'oil-in-water' mean?
In an oil-in-water mixture there is more water than oil.
The oil droplets are mixed into the water.
Butter is a water-in-oil emulsion. What does 'water-in-oil' mean?
In a water-in-oil mixture there is more oil than water. The water droplets are mixed into the oil.
What properties do emulsions have?
Emulsions are opaque and thicker than either of its separate parts.
This improves their texture, appearance and ability to coat and stick to solids.
Give an example of:
1. A natural emulsion.
2. A man-made emulsion.
3. An emulsifier.
1. Milk, Egg yolk.
2. Ice cream, butter.
3. Egg yolk, mustard powder.
Explain how these emulsifiers molecules are able to produce a stable mixture after shaking olive oil and water (3 marks).
An emulsifier has a hydrophilic head (1) and hydrophobic tail (1). This means the head is attracted to water and the tail is attracted to oil. Shaking breaks olive oil into droplets that they can't join up (1).
Oil droplets are surrounded by the hydrophilic heads. This keeps the droplets apart from the water, preventing them from joining together and separating.