Chemistry - C1.6 - Plant Oils

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C1.6.1 - Extracting Vegetable Oils

  • Vegetable oils found in some seeds, nuts and fruit - can be extracted by crushing and pressing plant material then removing impurities
  • Have lots of energy and important nutrients when eaten
  • Release lots of energy when burnt in air - used as fuels - make biofuels eg. biodeisel
  • Molecules have hydrocarbon chains - with carbon double bonds -> unsaturated, many double carbon bonds in each molecule -> polyunsaturated
  • Unsaturated oils react with bromine water - orange -> colourless
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C1.6.2 - Cooking with Vegetable Oils

  • Vegetable oil boiling points are higher than water's -> can be cooked at a higher temperature -> cooks faster, changes colour and texture of food, food absorbs oil, increasing the energy content
  • Unsaturated oils + hydrogen -> some/all of carbon double bonds = single bonds - hydrogenation or hardening (solid at room temperature - used as spreads and make pastries and cakes - require solid fats)
  • Hydrogenation - done at 60C using nickel catalyst
  • Hydrogenated oils - more saturated -> higher melting points
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C1.6.3 - Everyday Emulsions

  • Oil and water - don't mix, usually separate, forming two layers - when mixed, tiny droplets form that can be slow to separate - emulsion
  • Emulsions - opaque and thicker than what they're made from - improves texture, appearance and ability to coat and stick - milk, cream, salad dressing and ice cream, some water based paints and many cosmetics are emulsions
  • Emulsifiers - stop oil and water from separating into layers - most emulsions contain emulsifiers to keep them stable
  • Emulsifiers - have a small hydrophilic part ('head') that is attracted to water and a long hydrophobic part ('tail') that is attracted to oil
  • The hydrophobic part goes into the oil droplet so the droplet is surrounded by the hydrophilic part - this keeps the droplets apart in the water -> stopping them from joining together and separating
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C1.6.4 - Food Issues

  • Advs of vegetable oils and emulsifiers in food:
      - vegetable oils contain unsaturated fats - believed to be better for health than saturated fats
      - vegetable oils are high in energy and contain important nutrients
      - emulsifiers stop oil and water separating - makes food smoother, creamier and more palatable
  • Disadvs of vegetable oils and emulsifiers in food:
      - animal fats and hydrogenated vegetable oils contain saturated fats - linked to heart disease
      - emusified substances are high in fat and this may not be realised
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