Effects of processing conditions on the crystallization of cocoa butter.

摘要

This thesis is an investigation of how shear, cooling rate, and crystallization temperature affect the crystallization process and physical properties of cocoa butter. This research was executed with the objective of understanding how processing of cocoa butter affects the inclusion of lipid species onto the growing crystals, and the consequential effect on the different levels of structure of the resulting fat network such as polymorphism, microstructure and mechanical strength. Fractional attachment of different triacylglycerol molecules during the early stages of crystallization of cocoa butter was observed under static conditions. The crystalline material formed during the early stages of crystallization is enriched in highly saturated tristearin and highly unsaturated trilinolein. The outcome of the presence of such lipid species are changes in the crystal structure, as well as crystallization kinetics, microstructure and polymorphism. Cocoa butter crystallized statically has higher induction times, lower crystallization rates, is composed by a smaller number of larger crystalline microstructures, has slightly lower polymorphic transformation rates, and yields softer networks. The application of shear influences the progressive attachment of lipid species. By enhancing heat and mass transfer conditions in the melt, the initial crystals formed have a very homogeneous chemical composition. By avoiding fractionation of triacylglycerols, crystallization kinetics are accelerated. The resulting crystal networks are harder, have slightly higher melting points, and are composed of a larger number of small microstructures.