Polymorphism of POP and SOS. II. kinetics of melt crystallization

Abstract

Melt crystallization of the polymorphs of SOS, α,γ, pseudo-β′, β₂ and β₁. and of POP, α,γ, pseudo-β′₂ pseudo-β ₁, β₂andβ ₁was examined using pure samples (99.9%). Induction time τ for newly occurring crystals in the melt phase was measured with a polarizing microscope equipped with a temperature-controlled growth cell. Rate of crystallization, 1/τ, was obtained for each polymorph of POP and SOS whose identification was done with X-ray diffraction and differential scanning calorimetry (DSC). Two modes of crystallization, melt-cooling and melt-mediation, yielded approximately the same results for POP and SOS: (a) The rates of crystallization were always higher in less stable than in more stable forms,β ₂only crystallized via a γ-melt mediation, butβ ₁did not occur by the melt crystallization; (b) the rate of meltmediated crystallization was always higher than the simple melt-cooling as examined at the same crystallization temperature; (c) the occurrence behavior of the polymorphs differed between the simple-cooling and meltmediation. The results were related to the solidification behavior of the polymorphs of cocoa butter.