I want to determine Crude protein concentration of Cocoa husk using Kjeldahl, which estimates the protein in terms of nitrogen content using the equation N X 6.25 (Nitrogen content in amino acid is 16% and hence the factor 100/16=6.25).
Now my question is how are the Non Protein Nitrogen (NPN) taken into account for samples (such as cocoa husk) where nitrogen content in protein is not known. The Nitrogen in such cases can come from free amino-acids, peptides, Theobromine, pectin etc..
So, what should be the correction factor, because the samples (cocoa husk) when I extract protein and do protein quantification using Bradford, the protein content is 0.5 % whereas in Kjeldahl it gives a value of 7.8%.
I suggest that you consider reporting 'Kjeldahl N' without adjustment. Also when digesting make sure that the process is efficient for the N compounds present. You will need an efficient catalyst and a digest BP of close to 400 degrees C. The BP is primarily controlled by the K2SO4 concentration
I fully agree with Dr Milham.
You have to determine the NPN fraction separately eg as described in this link
http://www.sciencedirect.com/science/article/pii/S0958694616303582e
Thank you Dr. Milham and Dr. Kan.
This will help me a lot in getting the right answer to my question.
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