Performance evaluation of an enzymatic spectrophotometric method for milk urea nitrogen

Abstract

Our objective was to determine the within and between laboratory performance of an enzymatic spectrophotometric method for milk urea nitrogen (MUN) determination. This method first uses urease to hydrolyze urea into ammonia and carbon dioxide. Next, ammonia (as ammonium ions) reacts with 2-oxoglutarate, in the presence of reduced nicotinamide-adenine dinucleotide phosphate (NADPH) and the enzyme glutamate dehydrogenase (GlDH), to form l-glutamic acid, water, and NADP + . The change in light absorption at 340 nm due to the conversion of NADPH to NADP+ is stoichiometrically a function of the MUN content of a milk sample. The relative within (RSD r ) and between (RSD R ) laboratory method performance values for the MUN enzymatic spectrophotometric method were 0.57% and 0.85%, respectively, when testing individual farm milks. The spectrophotometric MUN method demonstrated better within and between laboratory performance than the International Dairy Federation differential pH MUN method with a much lower RSD r (0.57 vs. 1.40%) and RSD R (0.85 vs. 4.64%). The spectrophotometric MUN method also had similar method performance statistics as other AOAC International official validated chemical methods for primary milk component determinations, with the average of all RSD r and RSD R values being <1%. An official collaborative study of the enzymatic spectrophotometric MUN method is needed to achieve International Dairy Federation, AOAC International, and International Organization for Standardization official method status.

Interpretable machine learning reveals microbiome signatures strongly associated with dairy cow milk urea nitrogen

“…In addition, Portnoy et al. 13 measured MUN in 14 herds and found that MUN concentrations ranged from 11 to 23 mg/dL. In the measurement of MUN, Bittante 14 studied different breeds of dairy cows (Total 115819) and found that the mean value of MUN was 21.1 mg/dL.…”

Patterns of Fourier-transform infrared estimated milk constituents in early lactation Holstein cows on a single New York State dairy

“…The typical standard deviation of the differences among the reference chemistry and instrument-predicted values for the 14-sample calibration set was <0.015 g/100 g of milk for each parameter. Milk urea nitrogen (mg/100 g of milk) and milk-predicted blood nonesterified fatty acids ( mpbNEFA ), mBHB, and mACE (expressed as mmol/L) were measured by FTIR using a PLS model developed by Delta Instruments using parameter version numbers #502, #1603, #1601, #1602, respectively ( Bach et al, 2019 , 2021 ) and calibrated using reference chemistry values from an enzymatic MUN assay ( Portnoy et al, 2021 ).…”