What indicates the presence of a lipid during an emulsion test?

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The ethanol emulsion test is done to check for the presence of lipids, such as fats and oils. During the ethanol emulsion test, food is crushed and placed into a test tube. Enough ethanol is added to the test tube so that there is 2-3 centimeters of ethanol above the food sample. The top of the test tube is covered, shaken, and the solid is allowed to settle to the bottom of the test tube. The ethanol is then decanted into another test tube. Deionized water is added to this second test tube.

The interpretations of the possible results of the ethanol emulsion test are as follows.

  • If the color remains colorless, then no emulsification occurred.
  • If a suspension occurs at the top of the solution, then emulsification has occurred and the food sample contains lipids. The suspension occurs because lipids are hydrophobic and do not dissolve with water. Thus, when the water is added to the ethanol mixture, the lipids fall out of the solution and produce the cloudy surface that rise to the top of the test tube. 
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