Fourier Transform Infrared Spectroscopy (FTIR) for MUN analysis in normal and adulterated Milk

Abstract

The objective of this study was to evaluate the CombiScope FTIR equipment based on Fourier Transform Infrared methodology (FTIR), to assess the content of milk urea nitrogen (MUN) in Brazil. Repeatability and reproducibility of CombiScopeTM FTIR (Delta Instruments), and comparison with an enzymatic automated method (Chemspec® 150; Bentley Instruments) were tested to measure raw milk urea nitrogen (MUN). Additionally, MUN levels stability after storage of raw milk samples at 4ºC, and 20ºC for up to 15 days, and capability and precision to detect extraneous urea added as an adulterant to the milk were evaluated by FTIR equipment. There was a high correlation coefficient for the analysis of MUN by FTIR equipment, when compared with the automated enzymatic method, with no significant difference between both. MUN concentration in raw milk remained stable at temperatures of 4ºC for up to 15 days of storage, but after 3 days of storage at 20ºC there was an increase in the MUN levels. The CombiScope FTIR equipment proved to be a reliable method for analysis of MUN content in raw milk. However, results for MUN were not linear with the amount of extraneous urea added to raw milk, having a significant difference for samples when 40mg/dL of urea was added to milk.