Temperature dependent Raman and X-ray diffraction studies of anhydrous milk fat

Abstract

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 (1800-1700cm^-1) and the comparative study of the Raman-active CC (1660cm^-1) and CH (3000-2700cm^-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. CH stretching signals increased with polymorph stability, indicating the dominance of antisymmetric CH methylene vibrations as the anhydrous milk fats crystal lattice became more ordered. The change in intensity of the CH stretching bands as a function of temperature was used to probe the order-disorder transition.

Keywords: Anhydrous milk fats; Crystallization; DSC; Liquid state; Polymorphism; Raman spectroscopy; X-ray diffraction.