Polymorphism in cocoa butter

Aronhime, J.S. and Garti, N. (1988). Solidibcation and polymorphism in cocoa butter and the blooming problems. In N. Garti and K. Sato (Eds.), Crystallization and polymorphism of fats andfatty acids. Marcel Dekker, pp. 363-394. 

Schlichter-Aronhime, J., and N. Garti, Solidification and Polymorphism in Cocoa Butter and the Blooming Problem, in Crystallization and Polymorphism of Fats and Fatty Acids, edited by N. Garti and K. Sato, Marcel Dekker Inc., New York, 1988, pp. 363-393. 

Rossi, A., K.J. Roberts, M. Wells, M. Polgreen, and I. Smith, Polymorphism in Cocoa Butter Under Shear, in Confectionery Science II, Proceedings of an International Symposium, edited by G.R. Ziegler, Penn State University, University Park, PA, 1999, pp. 121-132. 

Mechanical, as opposed to viscosity, measurements on fats are comparatively rare. Often this is due to the brittle nature of the materials, for example chocolate. However, one approach is to observe the major transitions using the Triton materials pocket or constrained layer damped beam method. At present, however, absolute values of moduli cannot be obtained. Nevertheless, transitions between polymorphs in cocoa butter were measurable. 

Control of the polymorphic forms in cocoa butter is further compHcated by the presence of other fats such as milk fat. The fat in a chocolate can be likened to the mortar between the bricks in a mason s wall. The soHd particles in a weU-conched chocolate bed down better than the soHds in a coarsely refined and poorly mixed one (30). 

Fessas, D., Signorelli, M. and Schiraldi, A. (2005). Polymorphous transitions in cocoa butter -a quantitative dsc siuAy.Joumal Of Thermal Analysis And Calorimetry, 82(3) 691-702. 

Additionally, more than one subtype within the main polymorphic grouping has been identified in some fats. For example, six different polymorphic forms have been identified in cocoa butter, although there is stiU some debate whether they are all truly unique polymorphs (Table 2). Two p and two p forms have been identified for cocoa butter. These polymorphs have slightly different melting points, but they have X-ray spectra that fit within the definition of that polymorph. 

As for cocoa butter various modifications exist for hard fat, but their consequences are much less pronounced [8fj. Therefore, control of temperature during melting and cooling comes far less precise than in cocoa butter. Nevertheless, the polymorphism of hard fat is responsible for some physical processes including the process of secondary hardening (ageing) as described in Sect. 11.4.8. It is hardly possible yet to trace back this process to certain phase transitions. 

Table 2 Melting Ranges of the Different Solid Phases (Polymorphic Forms) Found in Cocoa Butter... 

Tempering. The state, or physical stmcture, of the fat base in which sugar, cocoa, and milk soHds are suspended is critical to the overall quaHty and stabiHty of chocolate. Production of a stable fat base is compHcated because the cocoa butter in soHdified chocolate exists in several polymorphic forms. Tempering is the process of inducing satisfactory crystal nucleation of the Hquid fat in chocolate. 

From DSC measurements it was deduced that the crystallinity of a freshly micronized sample is about 80% and that it crystallizes in the stable polymorphic form P2. Under the operating conditions mentioned, the PGSS process caused no degradation of cocoa butter and the product was a powder with a narrow and very controllable size-distribution. 

Ollivon, M., Loisel, C., Lopez, C., Lesieur, P., Artzner, F., Keller, G. 2001. Simultaneous examination of structural and thermal behaviours of fats by coupled X-ray diffraction and differential scanning calorimetry techniques application to cocoa butter polymorphism. In, Crystallization and Solidification Properties of Lipids (N. Widlak, R. Hartel, S. Narine, eds.), pp. 34-41, AOCS Press, Champaign, IL. 

The complexity of chocolate manufacture arises from the polymorphic nature of its constituent fats, which can come in at least five crystal forms, each with an individual melting point. Cocoa butter is chemically a multicomponent mixture of triglycerides and trace compounds (Davis and Dimick 1986). Approximately 85% of the composition consists of just three triglycerides POP ( 20%), POS ( 40%) and SOS ( 25%), where palmitic (P), oleic (O) and stearic (S) are the fatty acids attached to the glycerol base. The precise composition depends on factors such as growing conditions and therefore can vary between batches, especially from different geographic regions (Chaiseri and Dimick 1989). 

It was found that is a function of temperature but the model was found to give a better fit than analytical expressions like the Avrami model or the modified Gompertz model (Kloek, Walstra and Van Vliet 2000). The main advantage of this model is that as it is formulated as a differential equation, it can be used to predict isothermal as well as dynamic crystallization. However, this model does not consider the polymorphism of the material which is a critical point in the crystallization of cocoa butter. Another contribution is the model of Fessas et al. (Fessas, Signorelli and Schiraldi 2005) which considers all the transitions possible between each... 

Bricknell, J. and Hartel, R. W. (1998). Relation of fat bloom in chocolate to polymorphic transition of cocoa butter. Journal of the American Oil Chemists Society, 75(11) 1609-1615. 

An awareness of crystal-packing characteristics and polymorphism helps one to understand incompatibility problems of different fats. Polymorphism has several industrial implications in use of fats as shortenings, margarines, and cocoa butter. 

Proper control of the crystalline microstructure leads to products with the desired textural properties and physical characteristics. For example, tempering of chocolate prior to molding or enrobing is designed to control crystallization of the cocoa butter into a large number of very small crystals that are aU in the desired polymorphic form. When controlled properly, the cocoa butter crystals in chocolate contribute to the desired appearance (shine or gloss), snap, flavor release, meltdown rate upon consumption, and stability during shelf life (fat bloom). Similar... 

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