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.

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.

Crystallization of cocoa butter in the β phase directly from the melt is only possible by employing the memory effect of cocoa butter. Cocoa butter crystallized in the β phase, heated to the so-called maximal temperature (just above its melting end point), recrystallizes in the β phase after cooling to a crystallization temperature. The influence of the maximal and crystallization temperatures on the recrystallization behavior has been investigated for two cocoa butters. Rapid-starting recrystallization into the β(VI) phase and slow-starting recrystallization into the β(V) have been observed. It is concluded that rapid-starting recrystallization is induced by high-melting 1,3distearoyl-2-oleoyl-glycerol (SOS)-rich crystals. The two β phases were identified by X-ray powder diffraction and melting ranges. However, the X-ray powder diffraction patterns for the β phases depended on the composition of the cocoa butter and on the crystallization method used. Therefore, it was not possible to take any particular β(VI) X-ray powder diffraction pattern as a standard for the β(VI) phase of all cocoa butters.Paper no. J9843 in JAOCS 78, 919-925 (September 2001). KEY WORDS:Cocoa butter, crystallization, memory effect, seeding.Crystallization is a critical point in making chocolate and confectioneries. Poorly crystallized chocolate results in the formation of fat bloom, a grayish-white film at the chocolate surface. The chocolate seems aged and musty, which results in an increase in customer complaints to chocolate manufacturers. To obtain quality products, understanding and total control of the cocoa butter solidification process is indispensable. However, the crystallization behavior of cocoa butter is very complex, as cocoa butter may crystallize in many different polymorphic phases.Although this crystallization has been subject of thorough research for many years, no uniform nomenclature for the various phases of cocoa butter has been achieved. Vaeck (1) showed the existence of four phases and designated them by the Greek letters γ, α, β′, and β. Wille and Lutton (2) observed six different crystalline phases for cocoa butter, numbered with the Roman numbers I to VI. More recently, Van Malssen et al.(3) concluded from mechanically static solidification experiments that cocoa butter crystallizes in even more crystal modifications: a γ and an α phase, a β′ phase range, and two β phases were observed. In this chapter a combination of the nomenclature by Vaeck (1) and by Wille and Lutton (2) is used, resulting in the phases γ, α, β′, and two β phases: β(V) and β(VI). Each of the cocoa-butter phases has its own physical characteristics, such as diffraction properties, melting range, and relative stability.Since each phase gives a characteristic pattern in X-ray powder diffraction (XRPD), this technique is very well suited for identification of cocoa-butter phases (4; Fig. 1). Furthermore, in time-resolved XRPD experiments, phase transitions can be observed and monitored (3,5).The transitions from less stable to more stable phas...

The melting behavior of twelve different cocoa butter samples, in the β‐phase, has been investigated with real‐time X‐ray powder diffraction. The melting trajectory of each sample is characterized by three temperature values: a starting point, a point of maximum melting, and a point of complete melting. These points are determined by an analysis of the subsequent X‐ray diffraction patterns. A least‐squares analysis has been developed which allows the observed melting points to be related to the composition of the cocoa butter. This analysis shows that the melting behavior of cocoa butter can be described as a function of certain binary combinations of its major components.

n = even) triacylglycerols which are β′-stable, Guinier X-ray powder diffraction photographs were used to determine cell parameters and space groups. The powder diffraction patterns are consistent with a pseudo-orthorhombic unit cell with space group Ic2a. Only one axis is changing as a function of chain lengthening. The experimental results were used to propose a β′-crystal packing for triacylglycerols. In contrast to earlier proposed β′-crystal structures, the acyl chains of this structure are not tilted with respect to the methyl-end group plane. Furthermore, with only one molecule in the asymmetric unit, overall orthogonal chain packing is obtained when the intramolecular acyl zigzag planes are parallel.Paper no. J8979 in JAOCS 76, 603-609 (May 1999)KEY WORDS: Crystal packing, fat, triacylglycerol, X-ray diffraction.Polymorphism of fats and triacylglycerols (TAG) is a permanent subject of research because it may have important implications for the manufacturing of many different food products such as chocolate and margarine. Pure TAG crystallize in the different polymorphic phases α, β, and/or β′ and sometimes even several different β′-and/or β-polymorphs exist (1,2). The different polymorphic phases and their variants can be distinguished by X-ray diffraction through typical reflections in the fingerprint region of the X-ray powder diagram (d-spacings from 3.0 to 6.0 Å) (3,4). Table 1 shows the characteristics of the X-ray patterns of the different phases. Depending on the TAG type the most stable phase is either β′ or β. De Jong and Van Soest (5) showed that TAG of the type C n C n+2 C n and C n C n+4 C n+2 (n = even) are normally β′-stable. Most other types are generally β-stable. TAG mixtures also show differences in phase stability. For example, milk fat is β′-stable (6) while cocoa butter has β as the most stable phase (7,8).The phase behavior of pure TAG as well as TAG mixtures is very complex. Their phase transitions are generally irreversible and depend on experimental circumstances such as temperature and time, and their thermal history as is demonstrated by memory effects (9). Knowledge of this behavior, particularly the β′ → β phase transition is very important, especially for the chocolate industry, since unwanted phase transitions of cocoa butter may cause fat bloom, a white appearance of fat crystals on the surface. Therefore, control of these transitions determine to a large extent the quality of chocolate products.Crystal structure information of the different phases is indispensable to understand the mechanism of these transitions. Unfortunately, so far only crystal structures of β-polymorphs of pure TAG have been reported (10-15), all [β-1,2,3-tridecanoyl-glycerol, or tricaprin, or C 10 C 10 C 10 (β-CCC); β-1,2,3-tridodecanoyl-glycerol, or trilaurin, or C 12 C 12 C 12 (β-LLL); β-1,2,3-trihexadecanoyl-glycerol, or tripalmitin, or C 16 C 16 C 16 (β-PPP); and β-2-11-bromoundecanoyl-1,3-didecanoyl-glycerol, or C 10 C 11 Br C 10 (β-CL Br C)] crystallizing in space group P -1. The molecules are i...