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 ...
The crystallization behavior of milk fat was investigated by varying the cooling rate and by isothermal solidification at various temperatures while monitoring the formation of crystals by differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD). Three different polymorphic crystal forms were observed in milk fat: γ, α, and β′. The β-form, occasionally observed in previous studies, was not found. The kind of polymorph formed during crystallization of milk fat from its melted state was dependent on the cooling rate and the final temperature. Moreover, transitions between the different polymorphic forms were shown to occur upon storing or heating the milk fat. The characteristic DSC heating curve of milk fat is interpreted on the basis of the XRD measurements, and appears to be a combined effect of selective crystallization of triglycerides and polymorphism.Milk fat is one of the main constituents of milk and determines the specific properties of butter and cream. It is also an important ingredient in many bakery and confectionery industry applications. The various applications require different properties of milk fat, which in turn requires improved functionality control. The functional properties of milk fat are strongly related to the amount and type of milk-fat crystals at the temperature of application. The crystalline part of the fat determines to a large extent the firmness of products in which fat is present as the continuous phase, such as butter and butter oil, and the stability of products containing an emulsion of milk fat, such as cream. Milk fat has a broad melting range due to a large number of triglycerides with a wide range of chain lengths and degrees of saturation. Moreover, the phase behavior is complicated because of the polymorphism of the solid phase.Polymorphism of the crystallized phase is a general feature of triglycerides. The different polymorphic forms can be identified by X-ray diffraction (XRD). The polymorphic forms are characterized by the d-spacings (short-spacings) of the crystal lattices (typically between 3 and 6 Å) as observed in XRD patterns, which correspond to the distances associated with the lateral packing of the fatty acid hydrocarbon chains. Polymorphs with similar packing of the fatty acid hydrocarbon chains were found for pure tristearin (1), and for natural oils and fats (2), including milk fat (3). The d-spacings are characteristic for the type of polymorph, and this has led to the nomenclature given by Larsson (4) that is now widely accepted. Table 1 lists the d-spacings of the polymorphs of triglycerides (2). In general, the stable polymorph of triglycerides is either a β′-or a β-crystal form. The density of the β-crystal form is higher than that of the β′-crystal form, and this leads to more severe packing constraints for the first form as compared with the latter (5). As a result, asymmetrical triglycerides, i.e., triglycerides of the SSU or UUS type, in which the single unsaturated (U) or saturated (S) fatty acid resides in either the sn-1 or ...
In X-ray crystallography, a least-squares structure refinement is used to two purposes: to prove the correctness of the proposed model and to improve it. In electron crystallography, the same tool would be desirable. However, the standard programs for least-squares structure refinement used in X-ray diffraction may give wrong results using electron diffraction data because the kinematically calculated diffracted intensity is not valid for the interaction of electrons and crystals thicker than about 20 A for strong scatterers. In this paper, a new approach is presented that overcomes this problem and in addition takes into account all the advantages contained in dynamic scattering. The multislice method, well known in high-resolution electron microscopy (HREM), was combined with a least-squares algorithm, resulting in the multislice least-squares (MSLS) procedure. Experiments show that the atomic positions obtained by the new procedure are of the same accuracy as those obtained from single-crystal X-ray diffraction. However, the size of the single crystals used is much smaller (diameters down to +100 A). Also, light-atom positions can be determined with high precision by using data sets from crystal areas with different thicknesses. The multislice refinement gave good results up to 150 to 400A depending on the composition of the crystal, with R values based on the intensities of less than 5%. An additional advantage of the approach is that some extra quantities (e.g. crystal thickness, crystal orientation) can be refined at the same time. Acta Co'stallographica Section A
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.