Tests of Oils and Fats

Fats and oils are triesters of glycerol and higher fatty acids. At ordinary temperatures oils are liquids while fats are solids. Fats are present in gums, oils and milk foods. They are insoluble in water sparingly soluble in alcohol and soluble in chloroform. They serve as an excellent source of energy providers to the body.

Aim:

To study some simple tests to identify the presence of oils and fats in the given sample.

Theory:

Fats and oils are greasy in nature and on hydrolysis with aqueous or alcoholic sodium or potassium hydroxide liberate glycerol. Fats and oils are of vegetable or animal origin.

The following are the test to identify the presence of fats and oils.

  1. Solubility test
  2. Translucent spot test
  3. Acrolein test
  4. Baudouin test
  5. Huble’s test

(a) Solubility Test:

Fats are soluble in organic solvents like chloroform, alcohol etc. It is insoluble in water. So if the given sample forms an oily layer above the surface of the water then fat is present. Partially soluble in alcohol and fully soluble in chloroform then the presence of fat is confirmed.

Note: If the sample is miscible with chloroform and immiscible with water the fat presence is confirmed.

(b) Translucent Spot Test:

In this test the given sample to be tested is rubbed between the folds of filter paper. The appearance of translucent spot confirms the presence of fats in the given sample.

Note: If there is presence of translucent spot then the presence of fats is confirmed.

(c) Acrolein Test:

Fats and oils when heated with some crystals of potassium bisulfite KHSO4 in a test tube. A pungent irritating odor or smell of acrolein confirms the presence of fat or oil.

The chemical reaction is given below.

acrolein test

Note: If there is a pungent irritating odor then the presence of fats or oil is confirmed.

(d) Baudouin Test:

Baudouin test is applied to distinguish between the desi ghee and vanaspati ghee. Vanaspati ghee contains 5% sesame oil. Pure ghee does not contain sesame oil. Fats and oils are treated with 5ml of concentrated hydrochloric acid and 2% furfural solution in alcohol. After 5-10 minutes rose red colour appearance shows the presence of sesame oil in the given sample.

Note: This test is used to find out whether the given sample of desi ghee contains vanaspati or not.

(e) Huble’s Test:

This test is used to know the degree of unsaturation in the given sample. Oils on reaction with Huble’s reagent fads the violet colour of iodine then it is unsaturated and if the colour persists then the given fat or oil is saturated.

Note: In this test various oils can be compared on the basis of unsaturation.

Materials Required:

  1. Alcohol
  2. Chloroform
  3. Filter paper
  4. Potassium bisulfate
  5. Concentrated hydrochloric acid
  6. Furfural solution
  7. Test tubes
  8. Test tube holder
  9. Water bath
  10. Dropper
  11. Stirrer
  12. Bunsen burner

Apparatus Setup:

Tests of Oils and Fats

Procedure:

Preparation of Reagent:

Huble’s reagent – Mix equal volumes of 7% mercury chloride in alcohol with 5% solution of iodine in 96% of alcohol.

(a) Solubility Test:

  1. Take three test tubes which contains 5ml of given sample solution to be tested.
  2. Add 5ml of water to the first test tube and observe the solution.
  3. To the second test tube add 5ml of alcohol.
  4. To the third test tube add 5ml of chloroform.
  5. Observe the change in solubility of the given sample.
  6. If it is soluble in water then fat is absent, if its sparingly soluble in ethanol then fat is present and same for chloroform.

(b) Translucent Spot Test:

  1. Take the sample to be tested, press a little in the folds of the filter paper.
  2. On folding if there is the appearance of greasy spot indicates the presence of oils or fats.
  3. The spot grows larger on heating and drying the filter paper.

(c) Acrolein Test:

  1. Take the sample to be tested in a test tube.
  2. Add few crystals of potassium bisulfate to it.
  3. Heat the mixture and observe the change in odor.
  4. If there is pungent irritating odor then the presence of fate or oil is confirmed.

(d) Baudouin Test:

  1. Take 5ml of melted ghee in a test tube.
  2. Add 5ml of concentrated hydrochloric acid and 2-3% of furfural solution in alcohol to it.
  3. Keep it aside for 5 to 10 minutes.
  4. If there is the appearance of rose red colour then the given ghee contains vanaspati.

(e) Huble’s Test:

  1. Take two test tube and add 3ml of chloroform in each.
  2. Add cottonseed oil in one and linseed oil in the second test tube.
  3. Shake the mixture well and add 3 drops of Huble’s reagent in each test tube.
  4. The violet colour of iodine fades away in linseed oil test tube while the colour does not fade away in cottonseed oil.
  5. This shows that linseed oil is more unsaturated than cotton seed oil.

Observations and Inference:

Solubility test

If the sample is miscible with chloroform and immiscible with water the fat presence is confirmed.

Translucent spot test

If there is presence of translucent spot then the presence of fats is confirmed.

Acrolein test

If there is a pungent irritating odor then the presence of fats or oil is confirmed.

Results and Discussion:

The given sample contains __________ (fats/oils)

Precautions:

  1. Handle the chemicals with care. Not to inhale chloroform since it has anaesthetic effect.
  2. Use droppers to take the reagents from the bottle.
  3. While performing the experiment use hand gloves and lab aprons.

Viva questions:

1. What are fats?

Ans: Fat is an essential component of our diet and is important for good health. There are various types of fats, some of which are healthier than others. Fat, along with carbohydrates and protein, is one of three major macronutrients.

2. What is the difference between oils and fats?

Ans: Fats are molecules consisting of a chain of fatty acids with a glycerol head. There are several different types of fats determined by the number of carbon atoms in the chain of fatty acids and how many double bonds there are in the chain and where the bonds of figures are. Oils consist of a combination of different concentrations of fats.

3. How is the unsaturation in fats and oils determined?

Ans: The unsaturation in fats and oils is determined by Houble’s drop method.

4. What is the name of the compound formed when fats or oils reacts with potassium bisulfate?

Ans: Acrolein is the compound formed when fats or oils reacts with potassium bisulfate.

5. Name the test used to test the presence of unsaturation in fats and oils.

Ans: Huble’s test is used to test the presence of unsaturation in fats and oils.

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