Evaluation of a Rapid Method for the Determination of Urea in Cow’S Milk

Abstract

A rapid method for the determination of urea in milk was evaluated. The method employed was a urease/glutamate dehydrogenase procedure where the decrease in absorbante of NADH is monitored spectrophotometrically at 340 nm. The repeatability expressed as a coefficient of variation, was 1.4 % and 0.8 % for whole milk and skim milk, respectively. The accuracy of the method for urea determinations in whole milk was satisfactory (coefficient of variation, 2.6 %). Adding the preservative bronopol (0.02%) to the milk or freezing of the milk samples for one week did not alter urea levels significantly (P > 0.05). The storage of preserved whole milk in a refrigerator for 14 days, however, increased milk urea levels measured by 3.1 % (P < 0.001). It was concluded that the method evaluated is simple, rapid (40–50 samples/h) and yields reliable results also when whole milk is used. Since the determination of milk urea may be useful in assessing the feeding of energy and protein, the method is suitable for integration in the existing milk recording system in Sweden.