NMR Imaging of Dairy Products

Most MRI applications to dairy products are based on the sensitivity of relaxation time to chemical composition and changes in structure. It should therefore be borne in mind that for many dairy products the NMR relaxation signal is multi-exponential. This behavior is mainly explained by the chemical composition, since protons from water, fat, and protein contribute to the signal. Moreover, two phases can be observed according to the measurement temperature, i.e the liquid and solid fat. All these aspects complicate the interpretation of NMR relaxation time parameters and contrast in the MR image. Nevertheless, as the spin—spin relaxation time of protein protons and crystallized fat protons are very short, the image intensity is only dependent on the relaxation of the liquid phase, i.e the liquid fat proton and the water protons. Of course, if MRI acquisitions are performed at low temperatures where most of the fat is crystallized, the gray level intensity will describe only the water protons. This explains why most work has been done on low fat products or at low temperatures, or in high fat products such as cream and cheese, although some methods have been proposed to suppress water and fat signals selectively.