Effect of Pre-Crystallization Process and Solid Particle Addition on Cocoa Butter Crystallization and Resulting Microstructure in Chocolate Model Systems

Abstract

The kinetics of cocoa butter crystallisation during solidification and resulting compactness of structure during storage for different chocolate model systems were investigated with respect to solid particle addition (sugar and cocoa particles) and pre-crystallization process (seeded/non-seeded). Confocal laser scanning microscopy (CLSM) was used to monitor microstructural evolution during solidification and image analysis were applied in order to quantify the kinetics. In order to quantify the compactness of structure during storage the migration rate of small-molecules was measured at different length scales. On the meso-scale, FRAP (Fluorescence Recovery After Photobleaching) was utilized to quantify local migration rate solely in the fat phase, whilst HPLC (High Performance Liquid Chromatography) measurements were performed to assess the global migration of same molecules on a macro scale. Both techniques were used in combination with microstructure characterization using CLSM and supported by differential scanning calorimeter melting curves for estimating cocoa butter polymorphism. During solidification, seeded samples tended to form multiple nucleation sites, inducing rapid growth of a crystal network. The non-seeded samples showed an altering structure, with some domains developing large spherical crystals while in other domains a more heterogeneous microstructure resulted. For the non-seeded samples, the impact of solid particles on the crystallization kinetics was also most pronounced. Both FRAP and HPLC analysis proved to generate relevant information of the effect of pre-crystallization and solid particles on compactness of structure during storage. FRAP- measurements gave detailed information of the hetero- or homogeneity in microstructure within the cocoa butter whilst the HPLC clearly showed the impact of solid particles. The combination of the two techniques revealed that a compact and homogeneous structure obtained through fast crystallization during solidification is required in order to retard global migration in confectionery systems.