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ETHANOL EMULSION TEST FOR FATS AND OILS
The Ethanol Emulsion Test is a food test which determines the presence of a broad group of
naturally occurring compounds known as lipids. Lipids consist of fats andoils. Other lipid tests
include the Grease Spot Test and the Sudan Stain Test. The Grease spot test is performed on
fats - lipids which are solid at room temperature. Sudan stain colours lipids red, but is a less
common bench reagent than ethanol. The Ethanol Emulsion Test is the most common test
amongst the three.
PROCEDURE
Solid sample :
1. Crush the food sample and place in a dry test tube.
2. Add ethanol to about 2 cm3 above the level of the sample and shake thoroughly.
3. Allow the solid to settle (about 3 min) to allow the lipid to be extracted.
4. Decant the ethanol into another test tube.
5. Add 2 cm3 of deionized water to the second test tube
6. Make observations.
Liquid sample:
1.
2.
3.
4.
Add a few drops of the liquid food sample to a dry test tube.
Add 2 cm3 ethanol and shake it thoroughly
Add 2 cm3 of deionized water.
Make observations.
OBSERVATIONS & INTERPRETATION
OBSERVATION
 Solution remains colourless. No emulsion is formed.
 A layer of cloudy white suspension forms at the top
of the solution. (Upon close inspection you can see the
tiny globules of fat suspended in the solution. This an
emulsion. Foods with high lipid content have a ‘higher’
layer than foods with less).
INTERPRETATION
 Lipids are not present
 Lipids are present
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PRINCIPLE OF THE ETHANOL EMULSION TEST
The solubilities of lipids and ethanol are exploited in this test.
Lipids are non-polar organic compounds. Hence they are soluble in organic solvents such as
ethanol (alcohol), but insoluble in water.
Ethanol is an organic substance and so dissolves other organic substances; it is frequently used as
an organic solvent.
However ethanol is also miscible in water due to the presence of the hydroxyl (-OH) functional
groups and the shortness of its chain (2C). The hydroxyl group participates in hydrogen
bonding with water.
The hydrophobic interaction of the carbon in the short chain with water is not great and is
overcome by the hydrogen bonding.
Ethanol extracts the lipid from the crushed solid sample. As ethanol is miscible with lipids no
change is seen upon its addition to the solid and liquid samples.
The lipid spontaneously comes out of solution when water is added and is dispersed as micelles
(small droplets) throughout the solution of ethanol and water.( This happens as hydrophobic
portion of the lipid molecules project inwards and excludes the aqueous environment; the
hydrophilic portion (-COOH) group faces the aqueous environement.)
A layer is formed at the top as lipids are less dense than water. The droplets diffract light,
appearing cloudy white.
CONCLUSIVE TEST
A positive test shows conclusively that lipids are present - and not the other major biological
molecules.
1. Carbohydrates
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
Reducing sugars and non- reducing sugars - slightly soluble in ethanol and soluble in
water

Starch – insoluble in both ethanol and water
2. Proteins – insoluble in ethanol (the addition of ethanol is used to precipitate proteins)
3. Nucleic Acids – are insoluble in ethanol and soluble in water.
No change is seen in a negative test as there are no lipids to come out of solution.