Answer :
The Kjeldahl method measures nitrogen to estimate crude protein content because proteins typically contain 16% nitrogen. A multiplication factor of 6.25, derived from the average nitrogen percentage in proteins, is used to convert nitrogen content to crude protein. This method is widely used despite its limitation of potentially including non-protein nitrogen in its calculations.
The Kjeldahl method for determining crude protein relies on measuring the nitrogen content of a sample because proteins are made up of approximately 16% nitrogen. To convert the nitrogen content to an equivalent crude protein amount, we multiply by 6.25, as this is based on the average nitrogen percentage in proteins. For example, if a feed sample shows 7.0 g of nitrogen, the crude protein content is calculated by multiplying this figure by 6.25, resulting in 43.75 g of crude protein.
The Kjeldahl Analysis Procedure
This analysis is accurate and involves converting the organic nitrogen into ammonium sulfate using sulfuric acid, followed by a series of steps including neutralization, distillation, and titration. However, it may inaccurately measure non-protein nitrogen sources like urea or nucleic acids present in the sample, therefore, overestimating the protein content.
The reason we use the specific multiplication factor is because proteins, on average, are composed of 16% nitrogen by weight (100/16 = 6.25). So, when we determine the nitrogen content of a sample and want to know the total protein content, we use this multiplication factor to estimate the amount of protein that would contribute the measured amount of nitrogen.
