Journal Highlight: Raman spectroscopy of the polymorphic forms and liquid state of cocoa butter

Raman spectroscopy of the polymorphic forms and liquid state of cocoa butter

European Journal of Lipid Science and Technology, 2011, 113, 992-1004
Serge Bresson, Derick Rousseau, Supratim Ghosh, Mimoun El Marssi, Vincent Faivre

Abstract: Raman spectroscopy was used to characterize the polymorphs and liquid state of cocoa butter, with emphasis placed on the evolution of the ester carbonyl stretching region (1800-1700 cm^-1), along with complementary analysis and comparison of the Raman-active C-C (1200-1000 cm^-1), C=C (1660 cm^-1), C-H (3000-2700 cm^-1) and CH₂ (1500-1250 cm^-1) vibrational modes. Unique Raman signatures were obtained for all cocoa butter polymorphs, with their identity confirmed using DSC and XRD. The ester carbonyl region permitted polymorph discrimination due to differences in the number of modes, their relative frequencies and their full-widths at half-maximum. The C-C stretching modes, which provided insight into the trans/gauche content, were polymorph-independent. C-H stretching generally increased with polymorph stability, indicating the dominance of antisymmetric C-H methylene vibrations as the cocoa butter crystal lattice became more ordered. The change in the intensities of the C-H stretching bands used to probe the order-disorder transition of forms IV, V and VI hinted at pre-melt structural changes mostly in forms IV and V. Overall, Raman spectroscopy clearly demonstrated that the different functional groups studied could be characterized independently, allowing for the understanding of their role in cocoa butter polymorphism.

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