Chemical analysis of milk urea nitrogen (MUN).
By Francesco Bonicolini (cdr laboratories).


MILK UREA NITROGEN (MUN) is strongly influenced by the ratio between the digestible raw proteins and the energy of foodstuffs. Consequently, its content can constitute the basis for evaluating the suitability of a determined diet for dairy cattle for the purpose of obtaining a good quality product with high protein content.
Considering the low correlation that exists between the urea content in milk and the animal's characteristics, such as breed and age, it is possible to develop a monitoring system that uses milk urea nitrogen as an indicator of the efficiency of the feeding programs on dairy cattle farms [1, 2, 3, 4].
The test of milk urea nitrogen thus is of considerable importance for dairy farms, for the institutes assigned to the control and for dairy industry research laboratories.
Following a change in the requirements of consumers, who more and more prefer the protein component of milk with respect to the fat component, a price system has been developed that has reduced the economic weight of the fat component in favor of the proteic one.
The analysis of the protein content of milk is carried out by measuring the nitrogen present in the sample; however, high concentrations of urea in milk determine an increase in this parameter, which can mistakenly be considered proteic nitrogen. The analysis of the UREA makes it possible to distinguish the urea content from the true protein content in the milk.
Therefore, an analyzer capable of carrying out the chemical analysis of milk urea nitrogen is of great interest to companies that deal with the transformation and packaging of milk and its by-products, to institutes assigned to the control and to dairy industry research laboratories.
Recent studies have shown that high concentrations of MILK UREA NITROGEN have negative effects on cheese making processes. In particular, high concentrations of urea are the direct or indirect cause of numerous problems, such as an increase in coagulation time, the formation of a more fragile and less structured curd, premature development of irregular fermentations, and a more intense proteolysis. With the analysis of MUN, it is possible to avoid possible problems in cheese making processes [5, 6, 7, 8, 9].
An analyzer like CDR FoodLab capable of carrying out the urea test on milk is used with considerable profit in dairies.

[2] CARLSSON J., BERGSTROEM J., PEHERSON B. (1995). Variation with breed, age, season, yield, stage of lactation and herd in the concentration of urea in bulk milk and individual cow's milk. Acta Vet. Scand., (suppl.1), 36, 245.

[3] TEDESCO D., DELL'ORTO V., BALDI A., CHELI F., FERRARI C., PINOTTI L. (1998). Variazione del tenore in urea del latte nei primi 150 giorni di lattazione in bovine Frisone. Atti SISVET, 52, 463.

[4] GIARDINO R. (1996). L'urea nel latte: perché. Il latte-ARAL

[5] MARIANI P., BONATTI P., SANDRI S. "Contenuto di urea, pH, acidità titolabile e caratteristiche di coagulazione del latte di singoli allevamenti" ind. Latte 28, (1), 1 39, (1992).

[6] PECORARI M., MARIANI M.S., CALZOLARI M. G., TEDESCHI G. "Il contenuto di urea nel latte: variazioni e rapporti con i parametri tecnologici" Sc. Tec. Latt. Cas., 44, (3), 144 (1993)