Direct measurement of phase transitions in milk fat during cooling of cream - a low-field NMR approach

Low-field H-1 nuclear magnetic resonance (NMR) transverse relaxation (T-2) was measured during cooling (31-4 degrees C) of cream with low or high content of long-chain fatty acids (FA). Distributed analysis of the T-2, relaxation data revealed marked differences in the T-2 relaxation characteristics of the liquid fat population (10-100 ms), which was ascribed to differences in the size of the fat globules in the two types of cream. Principal component analysis (PCA) of the obtained T2 relaxation decay data showed clear shifts in NMR relaxation behavior at 17 and 22 degrees C for cream with low or high content of long-chain FA, respectively. Differential scanning calorimetric measurements on the creams revealed that these shifts took place at the onset of crystallization of fat. Consequently, the present study demonstrated that low-field NMR can be used to measure phase transitions in cream. (c) 2004 Elsevier Ltd. All rights reserved.