AOAC Official Method 998
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4FE74402F524401DAC84C68917332054 |
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0.02 |
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1 |
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日期： |
2024-7-30 |
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33.2.66,AOAC Official Method 998.07,Casein Nitrogen Content of Milk,Kjeldahl Method,Indirect Method,First Action 1998,Final Action 2001,(Applicable to fresh raw milk. Casein N content will decrease with,milk storage time due to casein breakdown even at 4°C. Casein content,of heat-treated milk will be artificially high because of whey,protein denaturation.),Results of the interlaboratory study supporting the acceptance of,the method:,sr = 0.015; sR = 0.022;RSDr = 0.560%;RSDR = 0.841%; r = 0.041;,R = 0.062 (calculated on a protein equivalent basis: N × 6.38).,sr = 0.0023; sR = 0.0034; RSDr = 0.560%; RSDR = 0.841%;,r = 0.0064; R = 0.0096 (calculated on a percent N basis).,Results of interlaboratory study are based on results from 10 collaborating,laboratories with statistical outliers removed from the,data sets.,A. Principle,Total N and noncasein N contents of milk are determined separately.,Difference between these 2 determinations is casein N content,of milk.,B. Determination,(a) Total nitrogen.—Determine as in 991.20 (see 33.2.11).,(b) Noncasein nitrogen.—Determine as in 998.05 (see 33.2.64).,C. Calculation,Subtract noncasein N content from total N content of milk to obtain,casein N. Multiply results by 6.38 to express casein on a protein,basis.,References: J. AOAC Int. 81, 763(1998).,International Dairy Federation (1964) Determination,of the casein content of milk. Int. Dairy Fed. Stand.,No. 29, Int. Dairy Fed., Brussels, Belgium.,Rowland, S.J. (1938) The determination of the nitrogen,distribution in milk. J. Dairy Res. 9, 42–46.,Revised: March 2002,. 2002 AOAC INTERNATIONAL……
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