Rizvi S S, Josephson R V
J Dairy Sci. 1975 Oct;58(10):1521-3. doi: 10.3168/jds.S0022-0302(75)84745-X.
Nonprotein nitrogen in pooled sweet (Cheddar and Dagano) and acid (cottage) wheys was estimated by currently proposed dialysis and chemical precipitation methods. Kjeldahl nitrogen analyses of (a) membrane retentates after water dialysis, and (b) 12% trichloroacetic acid plus .2% phosphotungstic acid filtrates indicated that nonprotein nitrogen values vary significantly with the method of sample preparation. Membrane porosity influence nonprotein nitrogen values for molecular weight cut-offs of 3500, 6000 to 8000 and 12,000 to 14,000. Dialyzable nitrogen values with all membranes were lower than 12% trichloroacetic acid soluble nitrogen for both wheys and higher than the 12% trichloroacetic acid + .2% phosphotungstic acid soluble nitrogen for all but the 3500 molecular weight cut-off membrane. The dialyzable nonprotein nitrogen fraction was heterogeneous but more that 80% was less than 3500 in molecular weight.
采用目前推荐的透析法和化学沉淀法，对混合甜型（切达干酪和达加诺干酪）和酸性（农家）乳清中的非蛋白氮进行了测定。对（a）水透析后的膜截留物和（b）12%三氯乙酸加0.2%磷钨酸滤液进行凯氏定氮分析表明，非蛋白氮值会因样品制备方法的不同而有显著差异。膜的孔隙率对截留分子量为3500、6000至8000以及12000至14000的非蛋白氮值有影响。对于两种乳清，所有膜的可透析氮值均低于12%三氯乙酸可溶性氮，且高于除截留分子量为3500的膜之外的所有膜的12%三氯乙酸 + 0.2%磷钨酸可溶性氮。可透析非蛋白氮部分是异质的，但超过80%的分子量小于3500。
