A complete isothermal phase-transition scheme of cocoa butter under static conditions is presented, based on time-resolved X-ray powder diffraction experiments. In contrast to what is known from literature, not only β V, but also β VI can be obtained directly through transformation from β′. Another remarkable result is that β′ exists as a phase range rather than as two separate phases. Within this β′ phase range no isothermal phase transitions have been observed. More detailed information concerning the observed cocoa butter polymorphs was obtained by determination of melting ranges, using time-resolved X-ray powder diffraction. Also standard X-ray powder diffraction patterns of the γ, the α, and the two β phases and parts of the β′ phase range have been recorded. The observed phase behavior of cocoa butter has been explained based on the concept of individual crystallite phase behavior of cocoa butter Paper no. J8719 in JAOCS 76, 669-676 (June 1999).Polymorphism, the occurrence of various solid phases (Table 1), of cocoa butter has a large impact on the product quality of chocolate and confectioneries. Obviously, intimate knowledge of the (isothermal) phase behavior of cocoa butter is of utmost importance to optimize production processes and to maintain product quality. An enormous amount of research has already been performed in the field of melting and crystallization of cocoa butter, its constituents, and related compounds (1-6). Typically, the work in this field is based on differential scanning calorimetry (DSC) experiments, often supplemented by X-ray powder diffraction (XRD). Recently Loisel et al. (7) used this combination to examine nonisothermal phase behavior of cocoa butter. The subcell of fat crystals (8-10) gives rise to a diffraction pattern between 3 and 5 Å that is unique for each different solid phase (1). Nevertheless, ambiguities and contradictions in the description of the polymorphism of cocoa butter still exist in literature (11). Like DSC, time-resolved X-ray diffraction (tr-XRD) (12) is a suitable technique to investigate solid-solid and liquidsolid-liquid phase transitions, but it has the advantage over DSC of giving unambiguous phase information. In previous work tr-XRD has been used to investigate the primary crystallization behavior of cocoa butter (13), the melting behavior of β-cocoa butter as function of the cocoa butter composition (14), and the occurrence of a memory effect (15). Results obtained so far have led to the current study on the isothermal phase behavior of static cocoa butter. As a main result of this study, a cocoa butter phase scheme covering all isothermal phase transitions in the temperature range from -20 to 40°C and a time range of 10 d can be presented. A standard XRD pattern has been recorded for each identifiable solid phase in this scheme. This enables determinations of differences, if any, between the various β′ and β subphases. In addition, the melting ranges of the various solid phases have been established.In the memory-effect studies, it was proposed ...

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The crystallization behavior of cocoa butter has been investigated by means of real‐time X‐ray powder diffraction. Two procedures have been followed: cooling from 60°C at a constant rate until maximum solidification has taken place; and cooling from 60°C in 2 min to a constant solidification temperature. It appears that all polymorphic forms of cocoa butter, with the exception of the β form, can be formed from liquid. The solidification temperature appears to be the most important crystallization parameter.

The crystal structure of the beta polymorph of tripalmitin (1,2,3-trihexadecanoylglycerol, beta-PPP) has been determined by single-crystal X-ray diffraction. The molecules crystallize in space group P1; in an asymmetric tuning-fork conformation. This structure and the already-known crystal structures of beta-tricaprin (beta-CCC) and beta-trilaurin (beta-LLL) could be matched in an overlap model. Apart from a difference in chain length, the three structures are almost identical. The overlap model can be used to predict the crystal structure of the other members of the C(n)C(n)C(n)-type (n = even) TAG series reasonably accurately. This is demonstrated by predicting the crystal structure for beta-trimyristin (beta-MMM) and successively comparing the experimental and calculated X-ray powder diagrams.

Direct β‐crystallization of different samples of cocoa butter has been investigated. The influence of the thermal history of cocoa butter on its phase behavior is defined as a memory effect. The chemical composition of cocoa butter has been related to the occurrence of the short‐term β‐memory effectvia statistical analysis of the results. We explain how this effect can be attributed mainly to stearic acid and its related triacylglycerols. The total phase behavior of cocoa butter is discussed on the basis of the results obtained from the series of three papers of which this is the last.