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Determination of the Total Nitrogen in Stored Milk by Nesslerization and by the Macro-Kjeldahl Methods

Department of Food Technology, University of Illinois, Urbana

ABSTRACT

The total nitrogen in milk can be determined by direct Nesslerization of the digested sample. Hetrick and Whitney (5) reported that this method for whole milk yielded results that averaged 2.5% lower than those obtained by the Kjeldahl-Gunning-Arnold method.

The direct Nesslerization method was used in this laboratory for determining the nitrogen distribution in sterilized milk held at different temperatures. The data showed unexplained variations in the total nitrogen of milk preheated to 140 and 180° F., sterilized at 305° F., homogenized and stored at 40, 70, and 100° F. Since there was no information in the literature to explain these variations, it was decided to compare the Nesslerization with the modified Macro-Kjeldahl method, which is the same as the official one (1) except for the following modifications: 5 ml. of milk was pipetted instead of weighed; 85 ml. of a mixture of sodium as determined by the modified Macro-Kjeldahl method gave consistent results, but the direct Nesslerization method gave varying results.