Phase behavior of cocoa butter in a two-step isothermal crystallization

Different analytical techniques (differential scanning calorimetry, pulsed nuclear magnetic resonance, and real-time X-ray diffraction using synchrotron radiation) were used to study the isothermal cocoa butter crystallization at temperatures between 19 and 23 degreesC. In this temperature range, the crystallization was shown to consist of two steps. In the first step, part of the melt crystallizes into the a polymorph, while in the second step a crystals transform into beta' crystals via a solid-solid transition. This second step starts before the melt-to-a transition is complete if crystallization is conducted at low temperatures. In the late stage of this solidification process, the a crystallization stops and only the polymorphic transition from alpha into beta' is observed. No beta' crystals are formed directly from the melt after the conversion has come to an end since an isosbestic point appears in the small-angle X-ray scattering patterns during the late stage of solidification that lasts until the very end of the beta' crystal formation.