SOP: Insoluble Impurities in Oils and Fats

GIFSQ — Global Institute for Food Safety & Quality

Principle

The impurities in fats and oils consist of dirt, meal and other foreign substances insoluble in kerosene and petroleum ether. The fat is dissolved away in hot kerosene and the insoluble residue is collected on a prepared Gooch crucible; the gain in weight of the crucible gives the insoluble impurities.

Apparatus required

• Gooch crucible, prepared with an approximately 2 mm thick pad of acid-washed asbestos using water, alcohol and ether in succession, dried to constant weight at 101°C ± 1°C, cooled in a desiccator and weighed
• Vacuum filtration assembly
• Oven, at 101°C ± 1°C
• Desiccator

Reagents

a. Kerosene.

b. Petroleum ether (or carbon tetrachloride) — for removing residual kerosene from the crucible.

Procedure

To the residue from the moisture and volatile matter determination, or a similarly prepared sample, add 50 ml of kerosene and heat on a water bath to dissolve the fat

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Filter through the prepared Gooch crucible using vacuum

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Wash with five 10-ml portions of hot kerosene, allowing each portion to drain before adding the next

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Wash thoroughly thereafter with petroleum ether or carbon tetrachloride to remove the residual kerosene

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Dry the crucible and its contents to constant weight at 101°C ± 1°C; cool to room temperature in a desiccator and weigh

Calculation

                        Gain in wt of crucible
% Insoluble impurities = ─────────────────────────── × 100
                           Wt of sample taken for moisture
                           determination

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.

Official and Tentative Methods, 3rd edn., American Oil Chemists’ Society, Vol. 1, Ca 4-25 (1975) — cited in the book.