Molecular Composition Dynamics and Structure of Cocoa Butter

Abstract

The present study endeavors to understand how small changes in the composition of cocoa butter affect its crystal habit, crystallization behavior, microstructure, and mechanical properties. Such compositional variations were attained by blending cocoa butter with 1 and 5% 1,2,3-tristearoyl-glycerol (SSS) or 1,2,3-trilinoleoyl-glycerol (LLL). Structural parameters such as crystallization kinetics, crystal structure, microstructure, and mechanical strength were obtained via differential scanning calorimetry (DSC), pulsed nuclear magnetic resonance (pNMR), X-ray diffraction (XRD), polarized light microscopy (PLM), and texture analysis. Changes in the triacylglycerol (TAG) profile of cocoa butter affected its crystal structure and therefore its functionality. The high melting saturated SSS becomes rapidly undercooled, reducing cocoa butter’s onset crystallization times and temperatures. SSS molecules are spatially bigger (i.e., straighter) relative to cocoa butter’s symmetric monounsaturated TAG (the unsaturated oleic acid in the sn-2 position introduces a kink into the TAG structure), and hence infringe upon the order of the crystal domain, reducing the crystal−melt interfacial tension, and delaying polymorphic transformations. On the other hand, the limited molecular compatibility between cocoa butter’s TAGs and the fully unsaturated low melting LLL prevents it from co-crystallizing with the bulk of cocoa butter’s TAGs, only slightly affecting the crystallization behavior, increasing the liquid fraction, having no impact on crystal structure yet accelerating polymorphic transformations into the stable β form.