Determination of ether extracts (EE) or crude fat

           In routine feed analysis, the lipids are determined as ether extract. In addition to lipids, ether dissolves plant pigments, such as chlorophyll, xanthophyll, carotene, and traces of other fat-soluble substances. Ether also removes certain essentials oils which are non-lipid products. Therefore, the term ether extract can not be accurately considered as fat but still common in use.

Principle

        Ether or petroleum ether or diethyl ether or any other fat solvent is volatilized and then condensed, the condensed sample is dropped on the sample containing the fat. The repeated volatilization and condensation extract the fat from the feed sample. It is then measured by weighing the ether extract or by calculating the decrease in weight of the sample.

Apparatus

  • Soxhlet apparatus
  • Desiccator
  • Hot air oven
  • Digital weighing balance
  • Porous thimble
  • Heating arrangement
  • Glass dish/China dish
  • Cold water arrangement

Reagents

  • Feed sample
  • Fat-soluble solvent e.g ether, alcohol, acetone, hexane, chloroform, carbon tetrachloride etc.

Procedure

          2 Gram oven feed sample is placed in a fat-free asbestos, porous thimble (made up of cellulose) and is covered with a cotton plug (fat-free) and place it in the jacket. If thimble is not available them feed sample may be wrapped in a filter paper and is placed in the sample jacket which is attached with a condenser having cold water circulation at the top for condensation and the receiving flask at the bottom containing fat solvent.
           The flask which contains a fat solvent is connected to the soxhlet apparatus and is heated, the solvent is volatilized and fumes go up via a tube in the upper part, where these are condensed due to cold water circulation. These condensed solvent drops are trickled down on the thimble, containing the feed sample, fat is dissolved and when a definite volume is attained, the solvent comes back in the receiving flask containing the fat solvent via a side tube. This volatilization and condensation is repeated until the color of the fat solvent around the thimble become colorless. This color is always due to fat-soluble pigments, (chlorophyll, xanthophyll, and carotene, etc).

Calculation

           The flask containing the dissolved fat is then removed and the content is transferred in a dry, clean, already weighed glass dish/flask/beaker,  and place it in a hot air oven for 4-5 hours for fat solvent evaporation, then the dish is taken out, place it in the desiccator for 3-5 minutes and it is again weighed. Continue this procedure until a constant weight is attained. The difference in weight would be the residue of ether extract.

                               Weight of residue
               EE %  = --------------------------  X 100
                              Weight of sample

 Or
                            Loss of weight of the sample
             EE % = -------------------------------------------- X 100
                                 Weight of the sample

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