23 December 2012

#32 Food test 3 - Emulsion (ethanol) test for Fats


This test is done to show the presence of lipids in a substance. The substance is first dissolved in ethanol. This solution is then dissolved in water. If lipids are present in the mixture, it will precipitates and forms an emulsion.








Process 
  • Add the food sample to 2 cm3 of ethanol, shake well.
  • Allow to settle in a test tube rack for 2 minutes for food to dissolve in ethanol.
  • Empty any clear liquid into a test tube containing 2 cm3 of distilled H2O.
  • MILKY-WHITE EMULSION is a positive result: lipid is present.
  • If the mixture remains clear, there are no fats present in the sample
Explanation
  • Lipids are insoluble in water and soluble in ethanol (an alcohol).
  • After lipids have been dissolved in ethanol and then added to H2O, they will form tiny dispersed droplets in the water. This is called an emulsion.
  • These droplets scatter light as it passes through the water so it appears white and cloudy.
Illustration




Additional source: cccmkc.edu.hk
                             Brilliant Biology Student  


11 comments:

  1. This comment has been removed by a blog administrator.

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  2. Does this experiment has any errors ?

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  3. Why are there oil drops if the fat is already dissolved in ethanol?

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    1. The ethanol is soluble in the water.
      The ethanol contains dissolved lipids.
      When the ethanol dissolves in water, the fats will separate as they are not soluble in the water.

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    2. when water is added to the ethanol with dissolved lipids the ethanol dissolves in water since it is soluble in water leaving the fats suspending.hope this will help

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  4. i think that is too concise for me .... wasnt this suppose to help me write my own

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    Replies
    1. yea boy it just confusing me more

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  5. Thx, it is really very simple, if anyone needs any help on the fat test or any of the othee protein, sugar or starch in food test then please comment and I am ready to give help.

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  6. After being dissolved solubley in ethanol, how do fat globules form a layer in water??

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  7. what if sodium hydroxide was used instead of water? what would be the result?

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