NPN and NCN determination in milk according to the Dumas combustion method

Milk is a source of animal protein of high nutritional quality. The nitrogen compounds of milk can be divided in: casein proteins and non-casein nitrogen (NCN). Among this, there are soluble whey proteins (WP), enzymes and non-proteins nitrogen substances (NPN), composed of urea, amino acids, uric acid, creatine, creatinine and ammonia. Although Kjeldahl is nowadays the most common method for determining nitrogen and protein contents in foods and feeds, Dumas method, shows a high level of precision and reproducibility compared to Kjeldahl method.