To the question: What apparatus or technique is used to know the nutritional value of food?
Several devices or techniques are used, from a simple calculator (or head for subtraction and multiplication) to gas chromatography equipment, to determine the percentage of saturated, monounsaturated and polyunsaturated fats. But let's go in parts, because the nutritional information of the food is analyzed by its components:
- Humidity: Amount of water that contains a food. It is determined by taking homogeneous sample of the food and keeping it at 103ºC until constant weight.
- Fats: On the one hand, the content is analyzed, by means of soxhlet extraction of the dry residue, and on the other, a transmethylation and subsequent analysis of the methyl esters of fatty acids is carried out by gas chromatography.
- Proteins: A kind of digestion of the food is carried out to release all the nitrogen (Kjeldahl's method) and the released nitrogen is subsequently determined. There are some factors of conversion of nitrogen to protein according to the food.
- Fiber: There are procedures to determine fiber, the part of foods that are polysaccharides that can not be assimilated.
- Dry residue: A homogeneous sample of the food is calcined to determine everything that is not "calcinable" carbon.
- Carbohydrates: Subtract 100 from all the above (here comes when you understand the joke of the calculator).
- Energy: By means of factors known to multiply by the content of carbohydrates, fats and proteins, the metabolic energy is calculated (yes, again with calculator).