Shear-Induced Crystal Formation and Transformation in Cocoa Butter

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• 作者：Stefan Padar ; Yvonne E. Mehrle ; Erich J. Windhab
• 刊名：Crystal Growth & Design
• 出版年：2009
• 出版时间：September 2, 2009
• 年：2009
• 卷：9
• 期：9
• 页码：4023-4031
• 全文大小：897K
• 年卷期：v.9,no.9(September 2, 2009)
• ISSN：1528-7505

文摘

We investigated shear-induced crystal formation and phase transformation of cocoa butter for a wide range of temperatures and shear rates. By simultaneously monitoring the wide-angle X-ray scattering pattern and the viscosity evolution, we characterized different crystallization events. The initial formation of polymorph form α and the transformation into the β_V polymorph was confirmed up to 24 °C. We quantified the acceleration of phase transformation by shear in cocoa butter. We also demonstrated that the same crystallization events are found in a highly concentrated model suspension at low macroscopic shear, which represents the flow conditions of chocolate in a temperer. There is strong evidence for fraction formation and compositional changes during growth of the crystallites. This led to the proposition of phase III being a mixture of cocoa butter in form α and a fraction of trisaturated triacylglycerols in form β′. Moreover, we investigated the gradual formation of a β_VI-like diffraction pattern during conditioning of β_V crystals under shear. Changes similar to single components transforming into their most stable form were an indication of local accumulation of higher melting triacylglycerols for the experimental conditions used.