GCSE Chemistry – Vegetable Oil

C1b 5.1 Extraction of Plant Oils

  • We can use distillation or pressing to extract vegetable oils
  • Distillation involves boiling the plant and condensing the evaporated oils released and removing water and other impurities
  • All vegetable oils have chains of carbon atoms with hydrogen atoms attached
  • Some vegetable oils have carbon=carbon double bonds. These are unsaturated oils
  • We can test for unsaturated oils using either bromine water or iodine solution:
    • Originally, bromine water is orange/yellow, but will turn colourless if it meets an unsaturated vegetable oil
    • Originally, iodine solution is red/violet, but will turn colourless also
  • unsaturated oils + bromine water → colourless solution unsaturated oils + iodine solution → colourless solution

 

C1b 5.2 Cooking with Vegetable Oils

  • Vegetable oils are useful in cooking because:
  • they have a high boiling point, and so foods can be cooked in them at very high temperatures
  • they allow food to absorb the oils, increasing their energy content
  • Vegetable oils can be hardened where they are reacted with hydrogen to increase their melting and boiling points
  • To make oils harden, you must use a nickel catalyst and carry it out at around 60oC
  • Oils that have been treated this way are called hydrogenated oils. Because they are solids at room temperature, it means they can be made into spreads (e.g. butter and margarine for bread, etc)

C1b 5.3 Everyday Emulsions

    • Oils do not naturally dissolve or mix with water
    • Oils can be used to produce emulsions which have special properties
    • Emulsifiers do not dissolve oils in water, they simply mix smaller droplets of oil in the water
    • Emulsions made from vegetable oils can be used in foods such as salad dressings and ice creams

 

C1b 5.4 What Substances are Added to our Foods?

 

    • We use food additives to improve the features of our foods
    • Approved European food additives are allocated E-numbers
    • The different E-numbers are:

E1…Colours

Improves the appearance of foods example; E150 – caramel

E2…Preserves

Helps to keep the foods’ lives last longer example: E211 – sodium benzoate

E3… Antioxidants

Stops foods from reacting with oxygen Example: E300 – vitamin C

E4… Emulsifiers,

Stabilisers and Thickeners Helps to improve the texture of the food Example:E440 – pectin

E5… Acidity Regulators

Helps to control the food’s pH Example: E501 – potassium carbonate

E6… Flavourings

Helps to improve the taste of the food. Example ,E621 – sodium glutamene

      • We can detect unknown food additives using chromatography, by comparing their chromatograms against those of substances we already know
      • We can also use a mass spectrometer