Temperature dependent Raman and X-ray diffraction studies of anhydrous milk fat
Résumé
Raman spectroscopy was used to characterize the polymorphs and liquid state of anhydrous milk fat, with emphasis placed on the thermal evolution of the ester carbonyl stretching modes (1800-1700 cm(-1)) and the comparative study of the Raman-active C=C (1660 cm(-1)) and CeH (3000-2700 cm(-1)) vibrational modes. Specific Raman signatures in the crystalline phase were found and attributed to the coexistence of two groups of triglycerides. This was confirmed using differential scanning calorimetry and X-ray diffraction methods. In the ester carbonyl band, the effect of changing temperature on both the number of modes and new defined intensity ratios was studied and enabled polymorph discrimination. C-H stretching signals increased with polymorph stability, indicating the dominance of antisymmetric C-H methylene vibrations as the anhydrous milk fats crystal lattice became more ordered. The change in intensity of the C-H stretching bands as a function of temperature was used to probe the order-disorder transition.