Total nitrogen was calculated with Kjeldahl method, I found different equations and factors
''Total nitrogen content of shrimp waste was determined using the Kjeldahl method. Separately, pure chitin was prepared to determine its nitrogen contribution allowing to estimate the crude protein content by multiplying nitrogen content attributed to proteins by the factor of 6.25''
''Total nitrogen and chitin nitrogen were estimated by the Kjeldahl method.Corrected protein was obtained by subtracting CN from TN and multiplying by 6.25, the Kjeldahl conversion factor for meat protein, assuming that protein has 16% nitrogen.''
(TN-CN)*6.25=11.25 protein content
‘’Total nitrogen present in shrimp shell protein hydrolysate was determined using the Kjeldahl method. Total protein was estimated by multiplying total nitrogen content in chitin by the factor of 6.25.’’
TP=TNC*6.25=10.625 protein content
protein (N 4.38) according to Crisan and Sands (1978),
3.7*4.38=16.21 protein
When protein is determined on the basis of total nitrogen content, a Kjeldahl factor of N x 4.38 (FAO, 1972) is commonly used (Levai, 1989), also on other edible fungi (Vetter and Rimoczi, 1993). The correction of the Kjeldahl factor from 6.25 to 4.38, however, is not based on strict analytical data but on common agreement.
3.7*4.38=16.21 protein
’Protein%=(N total % - C% x N% chitin) x f
where N Kjledahl is the total nitrogen content in the sample, C chitin is the chitin content in the sample, Nchitin is the nitrogen content in the chitin at complete acetylation (6.33%), and f is the remaining nitrogen to protein conversion factor (6.25)’’
P=(3.7-C x 1.7)x 6.25
For many years, the protein content of foods has been determined on the basis of total nitrogen content, while the Kjeldahl (or similar) method has been almost universally applied to determine nitrogen content (AOAC, 2000). Nitrogen content is then multiplied by a factor to arrive at protein content.
http://www.fao.org/3/Y5022E/y5022e03.htm
Following the nitrogen determination, crude protein content is calculated using a conversion factor. The original, and still frequently used, conversion factor 6.25 is based on an assumption that the general nitrogen content in food proteins is 16% and that all nitrogen in foods is protein-bound.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5789268/
For many years, the protein content of foods has been determined on the basis of total nitrogen content, while the Kjeldahl (or similar) method has been almost universally applied to determine nitrogen content (AOAC, 2000). Nitrogen content is then multiplied by a factor to arrive at protein content.
http://www.fao.org/3/Y5022E/y5022e03.htm
Several reliable methods for quantifying protein have been developed to simplify the process. These methods include Warburg-Christian, Lowry Assay, and Bradford Assay (all of which rely on absorbance properties of macromolecules). Bradford assay method is uses a dye to bind to protein.
https://en.m.wikipedia.org/wiki/Protein_methods
Chinaza Godswill Awuchi Thank you, I totally agree, furthermore, what about material contain aminosugar? we used the same factor 6.25?
Dear Yehya Boureghda
It depends on the method you are using. Method matter a lot in protein determination. Kindly check this article for different methods of protein analysis and the applicable conversion factor.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5789268/
Chinaza Godswill Awuchi I think that most available and easy method is Kjeldahl method, anyway, thank you for the useful information.
kind regards
Yehya Boureghda
The conversion factor depends entirely on the end use. If you quote protein based on N you must give the factor used.
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