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Determination of crude fat in foods by soxhlet extraction method

OBJECTIVES

To determine crude fat in foods by Soxhlet extraction method

INTRODUCTION

The crude fat content can be conveniently determined in foods by extracting the dried and ground material with petroleum ether or diethyl ether in Soxhlet extraction apparatus.

PRINCIPLE

Extraction of the crude fat is carried out either with petroleum ether or diethyl ether in a Soxhlet unit followed by volatilization of the solvent after extraction and determination of the mass of the residue.

REQUIREMENTS

Apparatus -Soxhlet apparatus

Reagents – Diethyl Ether — anhydrous or Petroleum ether (bp. 60-80°C)

PROCEDURE

Extract 2 g of the ground material in a continuous extraction apparatus with ether for 18 hours.

Remove the ether by distillation, followed by blowing with a stream of air, with the flask on a boiling water bath and dry in an oven at 110 ± 1°C till the loss in mass between two successive weighings is less than 2 mg.

Shake the residue with 2 to 3 ml of ether at room temperature, allow to settle and decant the ether.

Repeat the extraction until no more of the residue dissolves.

Dry the flask again until the loss in mass between two successive weighing is less than 2 mg. Record the final mass.

CALCULATION

Where,
M1 = mass, in g, of the Soxhlet flask with the extracted fat,
M2 = mass, in g, of the empty Soxhlet flask, and
M = mass, in g, of the material taken for the test.

RESULTS AND INFERENCE

Results of fat content should be reported to the nearest 0.1% (m/m). The difference between two single and independent results found by two analysts working in different laboratories on identical test material should not exceed :

≥ 10% (m/m) = 1% of fat content

4-10% (m/m) = 0.06% of fat content

1-4% (m/m) = 0.04% of fat content

≤1% (m/m) = 0.03% of fat content

The method is suitable for the determination of free fat content (crude fat) and may contain certain impurities soluble in ether. The method is only applicable to the food products having low moisture content.

PRECAUTIONS

  • The fat/oil obtained after drying should be clear and free from any particles. If the presence of particulate matter observed in the fat, the fat should be dissolved in petroleum ether again and filtered into other conical flask and dried.
  • If the charring of fat is observed during drying, discard the fat and repeat the experiment

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