Characterization of a semisolid state in milk fat through T-2* resolved T-1 distributions by time domain nuclear magnetic resonance

The solid-to-liquid ratio is an important parameter in the study of fats. M any methods can be used: dilatometry, differential scanning calorimetry (DS C), and nuclear magnetic resonance (NMR). However, below approximately 20 d egrees C, NMR gives much lower solid-to-liquid values than DSC. This differ ence can be attributed to the presence of a semisolid state, whose T-2 valu e would be of the order of 50-200 mu s, 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 th at in milk fat samples an intermediate component state clearly exists betwe en the solid and liquid phases, constituting only about 6% of an aged milk fat. The T-2* distribution of these components in this intermediate state s hows two peaks at about 60 and 170 mu s. We have shown from the T-2* resolv ed T-1 distribution of the peak, corresponding; to a T-2* Of approximately 60 mu s, that there is in the continuity in the crystalline phase. This fir st intermediate component state does not exist in pure triglyceride or in c ocoa butter, and is scarcely present in a tristearin crystal/soy oil suspen sion. We have attributed this first intermediate component to fatty acid re sidue extremities that protrude from the crystalline phase and/or to chain ends at the edges of holes created by short chains.