Structure of chocolate clarified with
synchrotron powder diffraction data
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 .
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.
 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