A beaker contains a thick liquid. How do you test whether it is a lipid?
The presence of lipids can be determined by performing the ethanol emulsion test.
Principle:
This test exploits the solubilities of lipids and ethanol.
Being non-polar organic compounds, lipids are soluble in organic solvents such as ethanol but insoluble in water. Ethanol is an organic substance and can dissolve other organic substances. Ethanol is also miscible in water due to the presence of the hydroxyl functional (-OH) groups and the shortness of its chain (only two carbon long). This hydroxyl group participates in the formation of hydrogen bonds with water.
The hydrophobic interaction of the carbon in the short chain with water is not too high and can be overcome by hydrogen bonding. Ethanol is used to extract the lipid from the crushed solid sample. As ethanol is miscible with lipids, there is no change when it is added to the solid and liquid samples. The lipid spontaneously comes out of solution when water is added and gets dispersed in the form of micelles throughout the solution of ethanol and water. As lipids are less dense than water, a layer is formed at the top. These droplets diffract light, appearing cloudy white.
Procedure:
I. Crush the food sample (solid/liquid) and place in a dry test tube.
II. Add ethanol to about 2-3 cm above the level of the sample and shake thoroughly.III. Allow the solid to settle to allow the lipid to be extracted.
IV. Decant the ethanol into another test tube.
V. Add 2 ml of de-ionized water to the second test tube
VI. Make observations.Observations & Interpretation
Solution remains colorless. No emulsion is formed. - Lipids are not present.
A layer of cloudy white suspension is formed at the top of the solution. - Lipids are present
The presence of lipids can be determined by performing the ethanol emulsion test.
Principle:
This test exploits the solubilities of lipids and ethanol.
Being non-polar organic compounds, lipids are soluble in organic solvents such as ethanol but insoluble in water. Ethanol is an organic substance and can dissolve other organic substances. Ethanol is also miscible in water due to the presence of the hydroxyl functional (-OH) groups and the shortness of its chain (only two carbon long). This hydroxyl group participates in the formation of hydrogen bonds with water.
The hydrophobic interaction of the carbon in the short chain with water is not too high and can be overcome by hydrogen bonding. Ethanol is used to extract the lipid from the crushed solid sample. As ethanol is miscible with lipids, there is no change when it is added to the solid and liquid samples. The lipid spontaneously comes out of solution when water is added and gets dispersed in the form of micelles throughout the solution of ethanol and water. As lipids are less dense than water, a layer is formed at the top. These droplets diffract light, appearing cloudy white.
Procedure:
III. Allow the solid to settle to allow the lipid to be extracted.
IV. Decant the ethanol into another test tube.
V. Add 2 ml of de-ionized water to the second test tube
VI. Make observations.Observations & Interpretation
Solution remains colorless. No emulsion is formed. - Lipids are not present.
A layer of cloudy white suspension is formed at the top of the solution. - Lipids are present
