Why is the conversion factor from Kjeldahl nitrogen to protein different for various foods, andhow is the factor of 6.25 obtained

The conversion factor from Kjeldahl nitrogen to protein can vary for different foods due to variations in their composition and amino acid content. The factor of 6.25 is obtained through a calculation based on the average nitrogen content of proteins.

Here are the steps to obtain the factor of 6.25:

1. The Kjeldahl method is used to determine the nitrogen content in a food sample. This method involves digesting the sample with sulfuric acid and then converting the nitrogen into ammonium sulfate.

2. Since proteins contain about 16% nitrogen on average, the nitrogen content obtained from the Kjeldahl method is multiplied by a factor to convert it to protein content.

3. The factor of 6.25 is derived from the assumption that proteins contain 16% nitrogen. To calculate this factor, the percentage of nitrogen in proteins (16%) is divided by 100%.

   16% / 100% = 0.16

4. To convert the nitrogen content to protein content, the nitrogen value obtained from the Kjeldahl method is divided by the factor of 0.16.

   Nitrogen content / 0.16 = Protein content

   For example, if the nitrogen content of a food sample is 1 gram, the protein content would be:

   1 gram / 0.16 = 6.25 grams

Therefore, the factor of 6.25 is used to convert the nitrogen content obtained from the Kjeldahl method to protein content in various foods.