C1-Plant oils and their uses Flashcards Preview

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Flashcards in C1-Plant oils and their uses Deck (15)
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1
Q

What are vegetable oils?

A

Vegetable oils are natural oils found in seeds, nuts and some fruit. These oils can be extracted.

2
Q

How are vegetable oils extracted?

A

The plant material is crushed and pressed to squeeze the oil out. Olive oil is obtained this way. Sometimes the oil is more difficult to extract and has to be dissolved in a solvent. Once the oil is dissolved, the solvent is removed by distillation, and impurities such as water are also removed, to leave pure vegetable oil. Sunflower oil is obtained in this way.

3
Q

What are the advantages of vegetable oils in cooking?

A

Vegetable oils have higher boiling points than water. This means that foods can be cooked or fried at higher temperatures than they can be cooked or boiled in water. Food cooked in vegetable oils:

cook faster than if they were boiled
have different flavours than if they were boiled.
4
Q

What are the disadvantages of vegetable oils in cooking?

A

However, vegetable oils are a source of energy in the diet. Food cooked in vegetable oils releases more energy when it is eaten than food cooked in water. This can have an impact on our health. For example, people who eat a lot of fried food may become overweight.

5
Q

What are the properties of saturated vegetable oils?

A

The fatty acids in some vegetable oils are saturated: they only have single bonds between their carbon atoms. Saturated oils tend to be solid at room temperature, and are sometimes called vegetable fats instead of vegetable oils.

6
Q

What are the properties of unsaturated vegetable oils?

A

The fatty acids in some vegetable oils are unsaturated: they have double bonds between some of their carbon atoms. Unsaturated oils tend to be liquid at room temperature, and are useful for frying food.

7
Q

What are the two categories of unsaturated oils?

A

monounsaturated fats have one double bond in each fatty acid

polyunsaturated fats have many double bonds.

8
Q

Which is healthier, unsaturated fats or saturated fats?

A

Unsaturated fats are thought to be a healthier option in the diet than saturated fats.

9
Q

What happens if you mix oil and water together?

A

If oil and water are shaken together, tiny droplets of one liquid spread through the other liquid, forming a mixture called an emulsion. However, if an emulsion is left to stand eventually the oil and water will separate.

10
Q

Why are emulsions useful?

A

Emulsions are thicker (more viscous) than the oil or water they contain. This makes them useful in foods such as salad dressings and ice cream. Emulsions are also used in cosmetics and paints.

11
Q

What are the two main types of emulsions?

A

oil droplets in water (milk, ice cream, salad cream, mayonnaise)
water droplets in oil (margarine, butter, skin cream, moisturising lotion).

12
Q

What do emulsifiers do?

A

Emulsifiers are substances that stabilise emulsions, stopping them separating out.

13
Q

How do emulsifiers work?

A

Emulsifier molecules have two different ends:
a hydrophilic end - ‘water-loving’ - that forms chemical bonds with water but not with oils
a hydrophobic end - ‘water-hating’ - that forms chemical bonds with oils but not with water.The hydrophilic ‘head’ dissolves in the water and the hydrophobic ‘tail’ dissolves in the oil. In this way, the water and oil droplets become unable to separate out.

14
Q

How can you test for unsaturated vegetable oils?

A

Using the bromine water test. Bromine water can also be used to determine the amount of unsaturation of a vegetable oil. The more unsaturated a vegetable oil is, the more bromine water it can decolourise.

15
Q

How are unsaturated vegetable fats hardened?

A

reacting them with hydrogen, a reaction called hydrogenation.
During hydrogenation, vegetable oils are reacted with hydrogen gas at about 60ºC. A nickel catalyst is used to speed up the reaction. The double bonds are converted to single bonds in the reaction. In this way unsaturated fats can be made into saturated fats – they are hardened.

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