Phase Transition Stability of Cocoa Butter Emulsions

The impact of tempering-crystallization on microstructure and stability of water-in-cocoa butter (w/o) emulsions was analyzed using differential scanning calorimetry (DSC). The type and volume fraction of the disperse phase, and cooling rate during DSC analysis were systematically varied. Freshly prepared emulsions were additionally characterized by microscopy and laser diffraction. Fresh cocoa butter emulsions were composed of small and well dispersed droplets of an average size of 2.24 mu m and 1.96 mu m for water and 50 % sucrose solution as disperse phase, respectively. The thermograms revealed that the dissolved sugar lowered freezing and melting temperature and, dependent on volume fraction, the dispersion in the oil phase led to a change in solidification behavior. The temperature at the solidification peaks gives qualitative information about droplet size whereas width and number of exothermic events are related to particle size distribution (mono/polydispersity and mono/multimodality) and microstructure. Emulsions with water as dispersed phase show a clear shift of the freezing peaks of the disperse phase which points on modified emulsion microstructure because of droplet coalescence, which is more pronounced at higher volume fraction and lower cooling rate. Emulsions with sucrose solution as dispersed phase showed the greatest stability, wherein the volume fraction and the cooling rate does not matter. The results allow conclusions about the mechanisms of crystallization processes in cocoa butter emulsions resulting as network crystallization.