The Spinsolve Ultra benchtop NMR spectrometer can be easily used to look at some of the main components in milk, like water, fat, and lactose. Milk contains around 87% of water, therefore the water signal dominates the spectrum and overlaps with the signal of some of the other components in the sample. Running a PRESAT experiment to suppress the water peak allows one to resolve the lactose and fat signals to perform an accurate quantification. Figure 1 shows the results of such measurements carried out on eight different commercial milk brands.
Figure 1: 60 MHz 1H NMR spectra of eight milk samples measured on Spinsolve 60 Ultra with solvent suppression (left). Plots on the right show their contents of fat (top) and lactose (bottom) calculated with the help of calibration curves.
Fat and lactose content obtained by NMR are in very good agreement with the values stated on the respective label of the products (Table 1). Water content in milk can be then calculated from the spectrum measured without solvent suppression, taking into account the fat and lactose content determined first from the PRESAT measurement.
Table 1: Fat and lactose content calculated for different brands of milk and compared to the values stated on the labels.