Soxhlet Extraction Method- Estimation Of Fat In Food

Fat plays an important role in many foods. Fat contribute to the flavour of food as well as it gives texture and also mouthfeel to the food. It is an important component which gives us maximum energy. Approximately 9 Kcal energy per gram. Extra intake of fat mostly leads to obesity and below the level lead to malnutrition. It nourishes the body with all the essential fatty acid that body can not synthesise and also help in building the body.

Hence there comes the need to measure the amount of fat present in food, so that we will have an idea of its amount and accordingly we can manage our diet. It also helps in extracting all the oil present in food.

There are two ways to find out the fat present in food, either by acid hydrolysis or by solvent extraction. The solvent extraction method is more pronouncedly known as Soxhlet method. It came into the scene in 1897. This method is widely used in almost all food industries and primarily used in oil extraction industries.


Lipid in food present in various forms like monoglycerides, diglycerides, triglycerides and sterol and free fatty acid and phospholipid and carotenoids and fat-soluble vitamins. Lipid is soluble in organic solvent and insoluble in water, because of this, organic solvents like hexane, petroleum ether have the ability to solubilize fat and fat is extracted from food in combination with the solvent. Later the fat is collected by evaporating the solvent.Almost all the solvent is distilled off and can be reused.


Primarily solvents like hexane and petroleum ether are in use due to their low boiling point. In addition to it, the solvent possesses following properties:

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1. Distribution Coefficient: This is the ratio (at equilibrium) of the concentration of solute in the extract and raffinate phases.

2. Selectivity (Separation Factor): If there are more than one solutes, then we have to for the appropriate solvent due to the chances of intermixing.

3. Insolubility of Solvent: The solvent should have low solubility in the feed solution.

4. Recoverability: The solvent should be thermally stable at the distillation temperature due to its volatility.

5. Density: Density should be lower than water.

6. Interfacial Tension: The larger the interfacial tension, the more difficult the dispersion of one liquid in the other will be.

7. Chemical Reactivity: The solvent should be stable chemically and inert.

8. Non-toxic


Soxhlet Extraction Method


First of all, we have to dry the product and remove moisture in order to facilitate entry of the organic solvent, because moisture restricts the entry of organic solvent. Then size reduction is there to increase the surface area and due to it, there is larger exposed surface. After this, we go for acidic hydrolysis which helps in breaking of protein fat emulsion and increases the availability of fat for the solvent. Furthermore, we can collect the solvent by distillation.


  • Weighing balance
  • Soxhlet apparatus
  • Drying oven
  • Thimble
  • Heating mantle
  • Glass rod
  • Desiccator with silica gel
  • Petroleum ether (Boiling temperature 60°-80°c)
  • Cotton plugs

 Soxhlet Extraction Method

Apparatus Used For Soxhlet Extraction Method


  1. First of all, rinse all the glass apparatus by petroleum ether and dry it in the oven at 102°c and after removing it keep in the desiccator.
  2. Weigh 5 gram of grounded and dried sample and place it in the thimble.
  3. Place the thimble in the soxhlet extractor.
  4. Take a 150ml round bottom flask and clean it and fill the flask with 90 ml petroleum ether.
  5. Place the whole setting on a heating mantle and allow the petroleum ether to boil.
  6. Continue the extraction process for several hours, almost 6 hours.
  7. Remove the condensing unit from extraction unit and allow the sample to cool down. Finally, it removes all the lipid.
  8. Collect almost all the solvent after distillation.
  9. Place the sample in the oven and after removing it place in the desiccator.
  10. Take the weight of the sample.
  11. As a result, we get a defat sample.
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Empty thimble= w1

Thimble with sample= w2

Weight of sample= p

Then crude fat percentage ig= (w2-w1) ⁄ p × 100

This method is an efficient method to extract all the fat present in the food. Hence it is used in oil extraction units for better recovery of oil. This method is also applied to the deoiled cake which is collected from screw impellers rather than high-pressure expression. It is also used in the analysis of fat present in the sample.


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