Cocoa butter (CB), the main fats and oils component of chocolate, shows six polymorphs; form I -VI, differ in melting point, thermodynamic stability and density. Among them, the form V is the most favored in chocolate production. There are methods such as tempering and seed crystal addition for efficiently crystallizing CB into form V in a short time. Based on previous studies, the most frequently used method to get form V is Tempering by temperature control. In the seed crystal addition method, “seed crystals” with a crystal structure like that of form V crystals are added to the CB melt from outside, the entire melt is crystallized into form V. In this study, we aim to clarify the crystallization process of CB by tempering and seed crystal addition using the multifaceted polymorphic evaluation method involving TEM and synchrotron radiation X-ray diffraction (SR-XRD) measurements.
In the seed crystal addition method, CB was melted at 55°C for 10 minutes, then cooled to 28°C while stirring. Form V and Form VI seed crystals were added, and the polymorphic transition around the seed crystals was observed for 2 to 3 hours at 20°C using TEM. In the tempering process, the crystallization process of CB in the form V during the melt-mediated transition was observed. Using TEM with a liquid cell, approximately 30 electron diffraction patterns of CB were measured under each condition. Additionally, using SR-XRD, the crystallization process of CB after seed crystal addition was measured for one hour at 20°C to observe the time-dependent changes.
In SR-XRD, regardless of the form of seed crystal, a direct transition from form II to form V observed. However, TEM revealed that adding form V seed crystals resulted in form IV topotactic growth on form II substrate, while adding form VI seed crystals resulted in heterogeneous nucleation due to seed crystals. The results of the crystallization process of CB by tempering will be shown on the day.