alexa Indirect and direct determination of the casein content of milk by Kjeldahl nitrogen analysis: collaborative study.
Chemical Engineering

Chemical Engineering

Journal of Analytical & Bioanalytical Techniques

Author(s): Lynch JM, Barbano DM, Fleming JR

Abstract Share this page

Abstract The classic method for determination of milk casein is based on precipitation of casein at pH 4.6. Precipitated milk casein is removed by filtration and the nitrogen content of either the precipitate (direct casein method) or filtrate (noncasein nitrogen; NCN) is determined by Kjeldahl analysis. For the indirect casein method, milk total nitrogen (TN; Method 991.20) is also determined and casein is calculated as TN minus NCN. Ten laboratories tested 9 pairs of blind duplicate raw milk materials with a casein range of 2.42-3.05\% by both the direct and indirect casein methods. Statistical performance expressed in protein equivalents (nitrogen x 6.38) with invalid and outlier data removed was as follows: NCN method (wt\%), mean = 0.762, sr = 0.010, sR = 0.016, repeatability relative standard deviation (RSDr) = 1.287\%, reproducibility relative standard deviation (RSDr) = 2.146\%; indirect casein method (wt\%), mean = 2.585, repeatability = 0.015, reproducibility = 0.022, RSDr = 0.560\%, RSDR = 0.841; direct casein method (wt\%), mean = 2.575, sr = 0.015, sR = 0.025, RSDr = 0.597\%, RSDR = 0.988\%. Method performance was acceptable and comparable to similar Kjeldahl methods for determining nitrogen content of milk (Methods 991.20, 991.21, 991.22, 991.23). The direct casein, indirect casein, and noncasein nitrogen methods have been adopted by AOAC INTERNATIONAL.
This article was published in J AOAC Int and referenced in Journal of Analytical & Bioanalytical Techniques

Relevant Expert PPTs

Relevant Speaker PPTs

Recommended Conferences

Relevant Topics

Peer Reviewed Journals
 
Make the best use of Scientific Research and information from our 700 + peer reviewed, Open Access Journals
International Conferences 2017-18
 
Meet Inspiring Speakers and Experts at our 3000+ Global Annual Meetings

Contact Us

 
© 2008-2017 OMICS International - Open Access Publisher. Best viewed in Mozilla Firefox | Google Chrome | Above IE 7.0 version
adwords