Characterization of a semisolid state in milk fat through T2 resolved T1 distributions by time domain nuclear magnetic resonance

The solid-to-liquid ratio is an important parameter in the study of fats. Many methods can be used: dilatometry, differential scanning calorimetry (DSC), and nuclear magnetic resonance (NMR). However, below approximately 20°C, NMR gives much lower solid-to-liquid values than DSC. This difference can be attributed to the presence of a semisolid state, whose T₂ value would be of the order of 50-200 μs, and which should give an NMR signal of 14 to 88.5% of the total signal of this phase at a time when the signal of the liquid phase is measured. Thus, such a state is seen partially as a liquid by NMR. In a previous study using time domain NMR, we have shown that in milk fat samples an intermediate component state clearly exists between the solid and liquid phases, constituting only about 6% of an aged milk fat. The T₂* distribution of these components in this intermediate state shows two peaks at about 60 and 170 μs. We have shown from the T₂* resolved T₁ distribution of the peak, corresponding to a T₂* of approximately 60 μs, that there is in the continuity in the crystalline phase. This first intermediate component state does not exist in pure triglyceride or in cocoa butter, and is scarcely present in a tristearin crystal/soy oil suspension. We have attributed this first intermediate component to fatty acid residue extremities that protrude from the crystalline phase and/or to chain ends at the edges of holes created by short chains.