Plant Oils & Emulsions

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  • Created by: safah1223
  • Created on: 28-03-16 17:31

Plant Oils

Some fruits, seeds and nuts are rich in oils that can be extracted. The pant material is crushed and the oil is removed by pressing or in some cases by distillation. Solid material is seperated by filtration. Water and other impurities are removed.

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Plant Oils

Vegetable oils are important foods and fuels as they provide a lot of energy. They also provide us with nutrients. Vegetabes have higher boiling points than water and so can be used to cook foods at higher temperatures than by boiling. This produces quicker cooking and different flavours but increases the energy that the food releases when it is eaten. Unsaturated fats are healthier than saturated fats.

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Unsaturated vegetable oils can be hardened by

  • reacting them with hydrogen
  • in the presence of a nickel catalyst
  • at a temperature of 60 degrees celcius 

Hydrogen react with the carbon-carbon double bonds so the oil becomes more saturated. The hydrogenated oils have higher melting points so they are solids at room temperature, making them useful as spreads (e.g. margarine) and in cakes and pastries.

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Testing for Unsaturation

Unsaturated fats contain a carbon-carbon double bond so can be detected by adding bromine water, which turns colourless. They have low melting points so are liquids at room temperature. Saturated fats do not have a double bond so bromine water stays orange. They have higher meting points so are solids at room temperature.

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Oils do not dissolve in water - a mixture of oil and water seperates into two layers. An emulsifier is a molecule which stabilises a mixture of oil and water helping the oil droplets to stay in the water for a longer time forming an emulsion. Emulsions are thicker than oil or water and provide better texture, coating texture and appearance. They are used in salad dressing, ice cream and painting.

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Examples of emulsifiers are egg yolk and mustard. Mayonnaise is an emulsion of oil and water using egg yolk as an emulsifier.

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Structure of Emulsifier Molecules

One part of emulsifier molecule (the head)  has an electrical charge (like an ion) and will dissolve in water but not oil. This is called a hydrophilic which mean water loving. The other part (the tail) is a long hydrocarbon which will dissolve in oil but not water. This part is called hydrophobic which means water hating.

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Structure of Emulsifier Molecules

The emulsifier molecule dissolves with the hydrophilic head in the water and the hyrdophobic tail in the oil droplet. A large number of emulsifier molecules keep the oil droplets dispersed in the water for a long time, forming an emulsion.

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