|MadSci Network: Chemistry|
"Crude fat" or "fat" is a somewhat difficult test to perform. One traditional way is to chop up the food and then extract it with an organic solvent. The solvent is then driven off under heat and the remaining "fat" weighed. Dividing this number by the weight of the sample gives the % fat in the food. Examples include the Soxhlet and Goldfisch methods. These methods are considered the "gold standard" for measuring fat. Another way is to release the fat by acid hydrolysis (digestion with acids). The fat goes to the top and is measured in a calibrated tube attached to the special bottle used. Examples include the Babcock and Gerber methods. You can also extract with an organic solvent and then use a high-accuracy hydrometer to measure the specific gravity of the extract. This method is not used much any more because of health and ecological problems with solvents. Nowadays, food companies typically use techniques based on instrumental methods. For example, near-infrared absorption is used on several types of foods to get moisture, fat and protein simultaneously. Differential nuclear magnetic resonance absorption (similar to hospital MRI techniques) is used to measure "fat" directly. The equipment for these tests is fairly expensive, costing about $20,000-$40,000. Another method is to measure moisture, protein and salt and subtract from 100% to get fat. This works for foods with no carbohydrate content, such as meat.
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