Food Lipids: Chemistry, Nutrition, and Biotechnology

Table 3 Nomenclature and Melting Point (�C) of Cocoa Butter Polymorphs
Wille and
Lutton [47]
Form mp
I
II
III
IV
V
VI
17.3
23.3
25.5
27.3
33.8
36.3
Lovegren
et al. [49]
Form mp
VI
V
IV
III
II
I
13.0
20.0
23.0
25.0
30.0
33.5
Hicklin
et al. [50]
Form mp
I
II
III
IV
V
VI
17.9
24.4
27.7
28.4
33.0
34.6
Davis and
Dimick [78]
Form mp
I
II
III
IV
V
VI
a From StOSt X-ray diffraction data and PStP X-ray diffraction data.
13.1
17.1
22.4
26.4
30.7
33.8
Hernqvist
[51] a
sub-�
�
�� 2
�� 1
�
�
Larson
[27]
�� 2 or �
�
� � �
��
� 2
�
morphs as determined by several groups. The definitions of cocoa butter polymorphs
follow several conventions [27,47,51]. Consistency throughout this chapter requires
the Wille and Lutton ‘‘I through VI’’ system [47] if thermal data are referenced, and
the Hernqvist [13] system if X-ray data are referenced. When appropriate, only the
Wille and Lutton system is used.
2. Polymorphic Formation and Transformation in Pure Cocoa Butter
A good description of the procedures necessary to form the six cocoa butter polymorphs
is available [50]. The microscopic analyses used in this work also provide
insight into the crystal habit of the forms. Each crystal formation procedure required
a different method of tempering. Other than rapid cooling of the melt to 0�C or
lower, no reference was made by any of the authors regarding the rate of cooling.
Neglect of this crystallization parameter or the assumption that the crystallization
temperature was most important is one explanation for the lack of reference to cooling
rate. In fact, van Malssen et al. [52] found that crystallization temperature, not
rate, determined which form would crystallize from the melt. However, their data
indicate a possible discrepancy. They stated at 0.25�C/min cooling, �� crystals formed
between 22�C and 26�C. At a cooling rate of 1�C/min, the � form crystallized at less
than 23�C. Further, at a cooling rate of 6�C/s, both � and � (sub-�) forms crystallized
at less than 3�C. These authors’ observation of no � crystallization after 10 days at
28�C is supported by recent real-time X-ray data, which showed no direct crystallization
of � (form VI) from cocoa butter melts [53]. As discussed above, cocoa
butter transforms monotropically, from the least stable to the more stable polymorphs.
Figure 8 depicts the polymorphic development in cocoa butter.
One unique consequence of the polymorphism of cocoa butter is called fat
‘‘bloom.’’ Investigations of bloom formation were published as early as 1937 [54].
Bloom occurs in chocolate, where it appears as a thin coating or scattered white
patches on the surface. Neville et al. [55] attempted to describe the mechanism of
bloom formation in terms of physical expansion of melting fat pushing higher melting
solid fat to the surface. Full [56] presented a good review of the current understanding
of bloom. Three possible mechanisms of bloom formation have been described
[57] and are listed in Table 4. Schlichter-Aronhime and Garti [58] argued
that because bloom results from a form IV to V conversion and from a V to VI
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.