Iwao Hachiya

Seeding effects on solidification behavior of cocoa butter and dark chocolate. I. Kinetics of solidification

Effects of seeding of fat crystals on the crystallization kinetics of cocoa butter and dark chocolate were examined with a rotational viscometer. The seed crystals employed were cocoa butter, 1,3-distearoyl-2-oleoylglycerol (SOS), 1,3-dibehenoyl-2-oleoylglycerol (BOB) and 1,2,3-tristearoylglycerol (SSS). The seed powders were prepared by pulverization below —50°C, the dimensions being in a range from 20–70 μm. Particular attention was paid to the influence of polymorphism of the seed crystal. We found that all of the above seed materials accelerated the crystallization, the degree of acceleration being in a following order; SOS (β1) > cocoa butter (Form V) > SOS (a mixture ofβ’ andβ2) > BOB (β2) > BOB (pseudo-β’) > SSS (β). Precise measurements of the crystallization kinetics showed that the most influential factors in the seeding effects are the physical properties of the seed materials—above all, thermodynamic stability, and similarity in the crystal structure to cocoa butter are the most determinative.

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

Melt crystallization of the polymorphs of SOS, α,γ, pseudo-β′, β2 and β1. and of POP, α,γ, pseudo-β′2 pseudo-β1, β2andβ1was 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,β2only crystallized via a γ-melt mediation, butβ1did 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.

Seeding effects on solidification behavior of cocoa butter and dark chocolate. II. Physical properties of dark chocolate

Demolding property just after solidification, we examined the polymorphism of cocoa butter in seed-solidified dark chocolate and fat-bloom stability through two thermocycle tests between 38 and 20°C (38/20) and between 32 and 20°C (32/20). The seed crystals employed are Form VI of cocoa butter,β1 of SOS (1,3-distearoyl-2-oleoyl-glycerol), pseudo-β’ andβ2 of BOB (1,3-dibehenoyl-2-oleoylglycerol) and β of SSS (1,2,3-tristearoylglycerol). The influence of the seed concentration was also examined. The seeding of cocoa butter (Form VI) and SOSβ1 caused the crystallization of Form V of cocoa butter and exhibited better demolding. As to the fat-bloom stability, the two, seed crystals were effective through the 32/20 cycle test, but the fat-bloom occurred through the 38/20 test. The seeding ofβ2 of BOB caused better demolding, crystallization of Form V of cocoa butter, and the most preferable fat-bloom stability; particularly, the seeding of 5 wt% concentration ofβ2 of BOB completely prevented the fat-bloom after the 38/20 test, although the seeding of all of the other materials and conditions caused the fat-bloom by this thermo-cycle test. The seeding of pseudo-β’ of BOB did not prevent the fat-bloom, although the demolding property was improved. In the case of the seed of β of SSS, both the demolding and fat-bloom stability were not improved. We concluded that the seeding ofβ2 of BOB revealed the most desirable, influences on the demolding and the fat-bloom stability of dark chocolate. This conclusion suggests the usage ofβ2 of BOB as the most preferable seed material in the solidification of dark chocolate, since the crystallization rate was also enhanced by this material as described in Paper I.

Polymorphism of POS. II. kinetics of melt crystallization

Melt crystallization of four polymorphs of POS, α,δ, pseudo-β′ andβ, was examined with pure samples (>99.9%). Induction time, τ, for newly occurring crystals was measured with a polarizing microscope equipped with a temperature-controlled growth cell. Rate of crystallization, 1/τ, was obtained for each polymorph, whose identification was done with x-ray diffraction (XRD) and differential scanning calorimetry (DSC). Two modes of crystallization, melt cooling and melt mediation, were applied. From these experiments, the following conclusions were obtained: (i) The rate of melt-mediated crystallization was always higher than of simple melt cooling; (ii) the pseudo-β′ form was crystallized in a wider range of temperature than the less stable δ form; (iii) the occurrence behavior of the polymorphs differed between simple melt cooling and melt mediation; (iv) the δ form was crystallized only by simple melt cooling in a narrow range of temperature, 25.5°C∼28.3°C. This means that there is a possibility that δ may result from racemic compounds that are crystallized in a specific manner. The experimental results are discussed in comparison to 1,3-dipalmitoyl2-oleoylglycerol (POP), 1,3-distearoyl-2-oleoylglycerol (SOS) and cocoa butter.

New chocolate technology on improvement of physical properties

To control and improve crystallization of Form V of cocoa butter, which is a main ingredient in the fat phase of chocolate, and fat bloom stability, we developed a new crystal seeding method using a crystal powder of the β2 form of BOB (2-oleoyl-1, 3-dibehenoylglycerol). The BOB β2 seeding can easily control the preferable polymorphic crystallization instead of a tempering process used in the chocolate industry. BOB β2 has a triple chain length structure and subcell packing of T//, which is same as Form V of cocoa butter. In addition, BOB β2 does not melt at higher temperature than the melting point of chocolate because its melting point is 51.4°C. From this reason, the 5% seeding of BOB β2 completely prevents the fat bloom formation on the surface of chocolate products even after heating at 38°C. The application of this method is practically used in the domestic chocolate industry.