Kjeldahl nitrogen analysis as a reference method for protein determination in dairy products

Measurement of total nitrogen by Kjeldahl analysis is the historical reference method for determination of the protein content of dairy products and is used for both calibration and validation of alternative methods for protein determination. Accurate evaluation of alternative methods is not possible if there is large uncertainty regarding the reference values. When Kjeldahl analysis is used to establish reference values, the performance of the Kjeldahl testing must be verified and within established expectations. Advice is given for Kjeldahl system optimization, evaluation of test results, and trouble-shooting. Techniques for successful Kjeldahl nitrogen analysis of dairy products other than milk are discussed.