Which statement correctly relates to Kjeldahl–based total protein determination?

Which statement correctly relates to Kjeldahl–based total protein determination?

• A. It measures peptide bonds
• B. It measures refractive index
• C. It uses UV absorption by aromatic residues
• D. It quantifies nitrogen content

Answer: (D)

The key idea here is that Kjeldahl-based total protein determination centers on measuring how much nitrogen is present in a sample to estimate how much protein there is. The process digests the sample to convert all organic nitrogen into a measurable form (ammonium) and then quantifies that nitrogen by distilling and titrating. From the measured nitrogen content, protein is estimated by applying a conversion factor, reflecting the typical proportion of nitrogen in proteins (about 16% nitrogen, so a common factor is 6.25, though the exact factor can vary for different food types). This method does not rely on peptide bonds, refractive index, or UV absorption by aromatic residues, which are used in other protein assessment approaches. The reason the nitrogen-quantification approach is the best answer is that Kjeldahl’s core purpose is to determine total nitrogen and then convert that to protein amount, rather than directly measuring bonds, optical properties, or UV characteristics.

The key idea here is that Kjeldahl-based total protein determination centers on measuring how much nitrogen is present in a sample to estimate how much protein there is. The process digests the sample to convert all organic nitrogen into a measurable form (ammonium) and then quantifies that nitrogen by distilling and titrating. From the measured nitrogen content, protein is estimated by applying a conversion factor, reflecting the typical proportion of nitrogen in proteins (about 16% nitrogen, so a common factor is 6.25, though the exact factor can vary for different food types).

This method does not rely on peptide bonds, refractive index, or UV absorption by aromatic residues, which are used in other protein assessment approaches. The reason the nitrogen-quantification approach is the best answer is that Kjeldahl’s core purpose is to determine total nitrogen and then convert that to protein amount, rather than directly measuring bonds, optical properties, or UV characteristics.