Molecular origins of cocoa butter triclinic polymorphism

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Mirzaee Ghazani, Saeed
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University of Guelph

This thesis is a comprehensive study of the solid-state properties of the main triglyceride molecular species in cocoa butter, namely 1,3-dipalmitoyl-2-oleoyl-glycerol (POP), 1-palmitoyl-2-oleoyl-3-stearoyl-glycerol (POS) and 1,3-stearoyl-2-oleoyl-glycerol (SOS). Two new triclinic crystal polymorphic forms (β3 and β2) of POS were discovered. Small and wide-angle powder x-ray diffraction patterns of these β3 and β1 crystal polymorphs of POS were identical to those of crystal forms V and VI in cocoa butter, while those of SOS and POP were not. Moreover, we also discovered that the crystal structure of CB in its meta-stable form IV and its transformation to form V was controlled by POS. The ternary phase behavior between POP, POS and SOS in their triclinic crystal polymorphic form was determined herein. POP:POS mixtures displayed a strong eutectic region. Also, POP addition always led to a decrease in the melting point of mixtures, while the opposite was true for SOS. A novel molecular structure was also identified with a melting point of 40 oC at 40:40:20 (w/w/w) POP:POS:SOS. In this work we showed that a novel algal butter was compatible with cocoa butter and could be used as an alternative for high SOS exotic butters in the design of CBEs. Additionally, we showed the the potential for synthesizing a CBM, a coco butter mimetic, for full replacement of CB in chocolate. The CBM was synthesized from natural fat fractions using a simple single step enzymatic conversion method. Since POS showed critical functionality in crystal polymorphism and melting behavior in ternary mixtures with POP and SOS, we recommend the inclusion of POS in the design of CBEs.

Cocoa butter, crystallization, POS molecule, Polymorphism, Enzymatic interesterification, Crystal structure, CBE