Determination of total fat content by Soxhlet extraction method

Materials and Apparatus required

Soxhlet extractor, round-bottomed flask, heating mantle, thimble, glass beads, mortar and pestle, analytical balance, Sample

Chemicals

n-hexane ( CH₃(CH₂)₄CH₃ ) or  low-boiling petroleum ethers

Principle

Soxhlet extraction is a continuous solid / liquid extraction invented in 1879 by Franz von Soxhlet. A solid which contains the material to be extracted is placed in what is called a thimble. A thimble is made out of a material which will contain the solid but allow liquids to pass through. A lot like filter paper. The thimble containing the material is placed in the Soxhlet extractor. An organic solvent like hexane or low-boiling petroleum ethers is then heated at reflux. As it boils its vapors rise up and are condensed by a condenser. The condensed solvent then fills up the thimble. After it fills with enough solvent it automatically siphons back down into the container of organic solvent. This process takes place over and over again until all the material to be extracted from the solid in the thimble is now extracted into the organic solvent.

                The Soxhlet method is one of the most popular methods used for lipid extraction from the natural products and foodstuffs.

Procedure

1.     Take sample of the food material.

2. Place an analyzed sample into a mortar and crush the mixture into fine pieces in a mortar and pestle.
3. Weigh about 40 g (±1 mg) of prepared sample and write down (m₀)_.
4. Transfer the mixed sample to thimble.
5. Add 3-5 glass beads into the clean and dry extraction flask and weigh it on the analytical balance with ±1 mg accuracy.
6. Write down the weight in the notebook (m₁).
7. Place the flask in the heating mantle and pour carefully about 350 ml of n-hexane.
8. Join the Soxhlet extractor with the flask.
9. Place the thimble with the sample into the chamber of the extractor.
10. Join the condenser with the extractor.
11. Join the rubber tubing with the condenser – cooling water should enter through the lower fitting and exit through the upper fitting.
12. Turn on the cooling water flow and begin heating the flask with a mantle.
13. Extract the sample for approximately 2 – 2.5 hours to collect the extract in n-hexane.
14. Adjust heat as necessary to achieve about 10 flushes per hour.
15. After extraction disconnect the condenser and Soxhlet extractor and round-bottom flask.
16. Cool down the flask and weigh it on the analytical balance with ±1 mg accuracy.
17. Write down the result in the lab-book (m₂).

Calculations

Total fat content, H, expressed in grams per 100 g of sample (or in percentage) could be calculated from the following formulae:

where:

m₀ – is the initial mass of the analyzed sample,

m₁ – is the mass of the clean extraction flask containing the glass beads,

m₂ – is the mass of the extraction flask containing the extracted lipid and the glass beads after solvent evaporation and cooled down to room temperature.

All the masses are expressed in grams [g].

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