Crude fat is the term used to refer to the crude mixture of fat-soluble material present in a sample. Crude fat also known as the ether extract or the free lipid content, is the traditional measure of fat in food products.
The lipid materials may include triglycerides, diglycerides, monoglycerides, phospholipids, steroids, free fatty acids, fat soluble vitamins, carotene pigments, chlorophylls, etc.
The common approach for total crude fat determination is based on the solubility of lipids in non-polar organic solvents such as hexanes, petroleum ether, or supercritical liquid carbon dioxide with or without a solvent modifier.
The two methods most commonly used to determine crude fat are wet extraction and dry extraction. Wet extraction is performed with the water remaining in the sample.
The Babcock method and the Mojonnier method both are wet extraction methods used for crude fat determinations in milk and milk products. These methods have also been applied to other products such as raw, canned, and frozen fish.
The Babcock method is one which releases the fat from the milk emulsion and measures the percentage directly in bottles calibrated for this.
The Babcock method does not determine the phospholipids in the milk products. It is not applicable to products containing chocolate or added sugar without modification of charring of chocolate and sugars by sulfuric acid.
A common dry extraction method is Soxhlet extraction method is performed with anhydrous ether. It is common crude fat determination method in many food. This technique extracts the crude fat into ether which is finally evaporated. Dry extraction is preferred when it is inconvenient to remove most of the water from a food. After extraction the solvent is evaporated, the residue weighed and reported as percent crude fat.
Three factors that affect crude fat analysis are moisture content, sample preparation, and extraction methodologies.
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