C1b 5

C1b 5 revision cards

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  • Created on: 20-05-10 18:18

5.1 extracting vegetable oils

Some seeds, nuts and fruits are rich in vegetable oils. The oils can be extracted by pressing followed by removing water and other impurities. Some oils are extracted by distilling the plants mixed with water. This produces a mixture of oil and water from which the oil can be separated.

The molecules in vegetable oils have hydrocarbons chains. Those with carbon-carbon bonds are unsaturated. If there are several double bonds in each molecule they are called poly unsaturated. Unsaturated oils will react with bromine or iodine. Bromine water is used as a test for an unsaturated compound.

Vegetable oils produce a lot of energy when eaten or when we burn then as fuels.

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5.2 cooking with vegetable oils

The boiling points of vegetable oils are higher than water, so food is cooked at higher temperatures in oil. This means it cooks faster. It also changes the flavour, colour and texture of the food. Some of the oil is absorbed and so the energy content of the food increases.

Unsaturated oils can be reacted with hydrogen so that some or all of the double bonds carbon-carbon bonds become single bonds. This is an addition reaction called hydrogenation and is done at about 60 degrees C using a nickel catalyst. Hydrogenation is used to increase the melting points of oils so they harden and become solid fats at room temperature. Solid fats can be spread and used to make cakes biscuits and pastries.

Oils- liquid at room temperature

Fats- solid at room temperature

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5.3 everyday emulsions

Emulsions are made from liquids that usually separate from each other. They are made by vigorously shaking, stirring or beating the liquids together to form tiny droplets of the liquid. The droplets are so small that they remain suspended in each other and are slow to separate.

Emulsifiers help keep the droplets to stay suspended and stop the liquids from separating. They do this because different parts of their molecules are attracted to the different liquids.

Emulsions are opaque and usually thicker than the liquids they are made from; this improves their texture, appearance and ability to stick to solids.

Milk, sauces, salad dressings and ice cream are examples of emulsions.

Solution- the substances mix completely (liquid becomes clear)

Emulsion- the liquids remain as tiny droplets (the mixture is not transparent)

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5.4 What is added to our food?

Substances added to foods to improve its appearance, flavour, texture and keeping qualities are called additives. Additives may be natural products or synthetic chemicals.

Some substances like salt, vinegar and sugar have been used for hundreds of years. There are six main types of additives:

· Colours

· Preservatives

· Antioxidants

· Emulsifiers

· Acidity regulators

· Flavourings

In the EU only permitted substances may be added to food and these are given e-numbers. Additives must be include in the list of ingredients on food labels and can be labbled with their full name or e-number.Foods are checked by chemical analysis to ensure only permitted additives have been used. The methods used include chromatography and mass spectrometry.

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5.5 vegetable oils as fuels

Vegetable oils produce a lot of energy when they burn. They can be treated to remove some chemicals and then used as a fuel in diesel engines. We can use waste vegetable oils from frying food as well as fresh oils.

Biodiesel can replace some or all of the diesel fuel produced form crude oil. Biodiesel is renewable because the plants are grown to produce vegetable oils. The plant material left after removing the oil can be used as food for animals

Biodiesel is less harmful to the environment than fossil fuels. The plants remove carbon dioxide from the air as they grow and so when we burn it there is no additional carbon dioxide released. Biodiesel produces no sulphur dioxide and it is more biodegradable than diesel oil.

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