Thermal and Mechanical Properties of Cocoa Butter Crystallized under an External Laminar Shear Field

Abstract

In this work, the effects of laminar shear on nanoscale structure and physical properties of triglyceride crystal networks were quantified. Cocoa butter (CB) was crystallized in the presence and absence of an external shear field. Samples were crystallized under a shear rate of approximately 340 s–1 in two different ways, by using a continuous Couette-type laminar shear crystallizer and by using a standard paddle mixer. Using different analytical methods and physical models, the mechanical strength and thermal properties of the crystallized CB were characterized. Cocoa butter crystallized under an external shear field had a stronger network with higher breaking force, Young’s, and storage modulus than statically crystallized samples. The sheared samples also had a smaller crystallite size (300 nm length, 130 nm width). Here we also show that the arrangement of the crystalline component influences the material’s strength. The Young’s modulus was increased by about 30% in samples that exhibited crystalline alignment. Moreover, higher average peak melting temperature (∼0.8 °C) and full width at half maximum of the thermogram curves, fwhm, (∼0.9 °C) were observed for the statically crystallized samples. In the presence of crystalline alignment, the melting point of cocoa butter was decreased slightly, about 0.5 °C. This work demonstrates the substantial effects of laminar shear applied during crystallization of cocoa butter on its functional properties including melting, hardness, and rigidity.