Structure of chocolate clarified with synchrotron powder diffraction data   

Dr. R. Peschar, HIMS, Universiteit van Amsterdam

Most chocolate eaters will have had the surprising experience that a newly opened bar of chocolate (pure or milk) has a grayish-white layer instead of the familiar chocolate color.  Most likely, this bar has fallen victim to the development of fat bloom. The cocoa butter in chocolate is responsible for the appearance of chocolate. In most consumer chocolate the cocoa butter is in its highest but one melting form, called β(V). Storage of β(V) chocolate at too high temperatures induces a transition to the most stable β(VI) form and this transition is commonly associated with the occurrence of fat bloom. To understand the β(V) → β(VI) transition, crystal-structure knowledge of the principal components of cocoa butter is required. The mono-unsaturated triglyceride 1,3-distearoyl-2-oleoylglycerol (SOS) comprises  ~ 25% of cocoa butter and is known to play a major role in the crystallization of cocoa butter into the β forms. Good quality single crystals of SOS are extremely difficult to obtain so we resorted to crystal structure determination using synchrotron powder diffraction data. Not only the crystal structure of the β(V)-type phase of  SOS has been determined, the first-ever crystal structure of a mono-unsaturated triglyceride, but also, very surprisingly, a crystal structure model of cocoa butter in the β(V) phase itself [1].

    In the presentation the following subjects will be discussed:
           The strategy and prerequisites to solve larger molecules from powder diffraction data.
           The crystal structure determination and models of SOS and cocoa butter.
           The implications for the β(V) → β(VI) phase transition and chocolate manufacturing.

[1] R. Peschar (a), M.M. Pop (a,b), D.J.A. De Ridder (a), J.B. Van Mechelen (a), R.A.J.
          Driessen (a,c), H. Schenk (a) J. Phys. Chem. B. 108(40), 15450-15453 (2004)

          (a) Laboratory for Crystallography, Van t Hoff Institute for Molecular Sciences, Faculty of Science, University of Amsterdam 
(b )Now at:  Avantium Technologies BV, Amsterdam.
          (c) ICT dept., Faculty of Science, University of Amsterdam