JCAM No.105-R2
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Japan Customs Analysis Methods
No. 105
Quantitative Analysis of Crude Protein
(Issued in June 1999)
(Updated in November 2013)
1. Scope
This analysis method is applied for determination
of crude proteins in products containing proteins, such
as food products.
2. Procedure
Determination of crude proteins is performed
using an automatic Kjeldahl nitrogen analyzer. The
analyzer should be operated in accordance with the
manufacturer’s instruction.
The digestion temperature and time must be set to
conditions under which nitrogen recovery ranges from
98% to 100% when tryptophan (JIS special grade) is
used as a reference sample.
Here, conversion factors from Kjeldahl nitrogen to
crude protein are as follows:
Milk and dairy products 6.38
Wheat and unpolished flour 5.83
Rye, barley, and oat 5.83
Rice 5.95
Soy bean and its products, excluding
soy protein isolates
5.71
Others 6.25
3. References
（1）AOAC 991.20
（2）Codex Standard 175-1989
（3）FAO FOOD AND NUTRITION PAPER 77 (2003)
“Food energy – methods of analysis and conversion
factors”
（4）Standard Tables of Food Composition in Japan,
Fourth Revised (1996)