1H nuclear magnetic resonance relaxometric characterization of fat and water states in soft and hard cheese

Abstract

The aim of this work was to study the spin–spin (T2) relaxation components of one hard cheese and three soft cheeses to characterize fat and water states. NMR signals were measured at 6 °C with a 0·47 T NMR device. The transverse relaxation decay was fitted using the Marquardt method. The T2 relaxometric behaviour of the cheeses under consideration was characterized by four relaxation components. To understand the chemical composition of each NMR component, we studied anhydrous milk fat extracted from each cheese analysed. At 6 °C, the fat was 60% crystalline. In cheese, the solid fat was found mainly in the shorter relaxation component with a T2 of 17 μs. The intensity of the NMR relaxation with a T2 > 1 ms was explained by the amount of water, liquid fat and proteins, and the associated relaxation time varied as a function of the process used. The composition of each relaxation component was confirmed by the temperature effect and the influence of the fat content on the NMR cheese signal. NMR relaxometry was able to provide information on water behaviour (i.e. the quantity and level of interactions with proteins) and on the solid[ratio ]liquid ratio of anhydrous milk fat in the cheese.