Effect of temperature on recrystallization behavior of cocoa butter

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 1,3-distearoyl-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.     

Characterizing cocoa butter seed crystals by the oil-in-water emulsion crystallization method

Unambiguous quantitative evidence for the catalytic action of seed crystals in cocoa butter is presented. We used an ultrasound velocity technique to determine the isothermal growth of solid fat content in cocoa butter oil-in-water emulsions, in which the probability of finding a seed crystal in any one droplet was around 0.37 at 14.2°C. The upper limit for the size of seed crystals in West African cocoa butter was around 0.09 μm, the Gibbs free energy for nucleation was 0.11 mj m⁻², and the concentration of seed crystals was in the range of 10¹⁶ to 10¹⁷ m⁻³. X-ray diffraction measurements showed that emulsified cocoa butter crystallizes in the α polymorph and does not appear to transform to the β′ form within the first 25 min of crystallization. Primary nucleation events in cocoa butter emulsions are accounted for by seed crystals. Collision-mediated nucleation, a secondary nucleation mechanism, in which solid droplets (containing seed crystals) catalyze nucleation in liquid droplets, is shown to account for subsequent crystallization. This secondary nucleation mechanism is enhanced by stirring.     

The effect of shear on the crystallization of cocoa butter

This paper examines the effect of shear on the crystallization of cocoa butter using a combination of three different experimental techniques and a single crystallization temperature of 20°C. Rheological measurements were carried out to study the effect of a shear step on the crystallization kinetics of the fat. Without a shear step, little rheological change was observed at 20°C; however, with the application of a shear step the onset of significant rheological change occurred and was strongly influenced by the magnitude of the shear step. Detailed crystallographic measurements could be made with in situ X-ray experiments during flow-induced crystallization. The imposition of continuous shear changed both crystal polymorphic structure and crystallization kinetics in a systematic way. Finally, optical measurements were used to follow changes in crystal morphology as a consequence of continuous shear. These results revealed the form and kinetics of crystal growth. In general the results complemented each other, and an overall picture of the way shear influenced cocoa butter growth could be formed. The observations could be the basis for a future mathematical model of growth kinetics and provide insight into the way shear influences crystallization kinetics, morphology, and polymorphic structure.     

Real-time X-ray powder diffraction investigations on cocoa butter. I. temperature-dependent crystallization behavior

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.     

Characterization of cocoa butter substitutes,milk fat and cocoa butter mixtures

The melting properties and polymorphic behavior of binary and ternary blends of cocoa butter substitutes (CBS), cocoa butter (CB), and milk fat (MF) were studied by using pulsed nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and X‐ray diffractometry (XRD). Hydrogenated palm kernel stearin (HPKS) and hydrogenated palm kernel olein (HPKO) were chosen as the two CBS feedstock fats. Both CBS/CB binary blends displayed significant eutectic behaviors. Multiple melting peaks and eutectic effects were observed at 30–50% addition levels of CB to HPKS. The range was broader in HPKO/CB blends. Dilution effect was observed in both CBS/MF blends while slight monotectic effect was also observed in HPKO/MF blends. Ternary phase diagrams and melting curves showed that eutectic effects existed in both ternary blends and the degree of interaction depended on the content of CB and MF. XRD results showed that when pure fat component in each blend exceeded 80%, its polymorphism dominated in the ternary blends. However, when CBS/CB or MF /CB were added at a comparative content (blends D and F), both β and β′ form existed. Practical applications: Phase properties of fat blends may have significant effects on the sensory characteristics and physical properties of the final products, such as hardness, brittleness, and the bloom formation. This study evaluates the melting properties and the polymorphic characteristics of fat blends of constituents with potential use in the manufacture of confectionery products. A comprehensive analysis of binary and ternary fat blends was conducted in order to provide a guide for compound chocolate production formulation.     

Real-time X-ray powder diffraction investigations on cocoa butter. II. The relationship between melting behavior and composition of β-cocoa butter

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.     

Effects of ultrasonic irradiation on crystallization behavior of tripalmitoylglycerol and cocoa butter

Effects of application of ultrasonic power (20 kHz, 100 W) on the crystallization behavior of tripalmitoylglycerol (PPP) and cocoa butter have been examined in terms of rate of nucleation and polymorphic control. High-purity PPP (>99%) and low-purity PPP (>80%) samples were employed to mimic real fat systems, which usually have higher concentrations of minor components in addition to the main component. For both the high-purity and low-purity PPP, the application of ultrasonic power accelerated the rate of nucleation as measured by induction time for the occurrence of crystals and by the number of crystals nucleated. As for the polymorphic influences, the nucleation of both the β′ and β forms was accelerated by the ultrasound, yet the β′ form nucleation was more accelerated when the low-purity PPP samples were employed. As for cocoa butter, sonication for a short period accelerated the crystallization of Form V. The present results indicate that ultrasound irradiation is an efficient tool for controlling polymorphic crystallization of fats.     

Phase behavior and extended phase scheme of static cocoa butter investigated with real-time X-ray powder diffraction

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     

Real-time X-ray powder diffraction investigations on cocoa butter. III. Direct β-crystallization of cocoa butter: Occurrence of a memory effect

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.     

Phase transitions and polymorphism of cocoa butter

The polymorphism and phase transitions of cocoa butter (CB) have been reexamined separately by differential scanning calorimetry (DSC) and X-ray diffraction as a function of temperature (XRDT) at scanning rates between 0.1 to 5°C/min and 0.1 to 2°C/min, respectively. A new instrument, which allowed simultaneous DSC and XRDT recordings from the same sample by taking advantage of the high-energy flux of a synchrotron, was employed for characterization of the intermediate phase transitions. These techniques allowed us to confirm the existence of the six polymorphic forms of CB (called I to VI) by in situ characterization of their formation in the DSC + XRDT sample holder. A detailed study of Form I structure led us to propose a liquid-crystal organization in which some of the chains displayed sharp long-spacing lines (d₀₀₁=52.6±0.5 Å) and a β′ organization (4.19 and 3.77 Å), while the others remained unordered with broad scattering (maxima at about 112 and 36.5 Å). The organization of this liquid crystalline phase is compared to that of fat and oil liquids. This liquid crystalline phase progressively transformed on heating into a more stable phase (Form II, α type, d₀₀₁=48.5±0.5 Å and short-spacing at 4.22 Å). Form III was only observed in a sharp temperature domain through its specific short-spacings. The existence of the six species has been essentially related to the crystallization of monounsaturated triacylglycerols (TAG), while trisaturated species were found partly solid-soluble in these six polymorphic forms. An insoluble fraction crystallized independently of the polymorphism of the monounsaturated TAG in a separate phase with long-spacings that were either of the α (49.6±0.5 Å) or β (44.2±0.5 Å) form. In mixture with Form V, this fraction melts and solubilizes in the liquid phase at 37.5°C. Isolation of these high-melting crystals shows a melting point of about 50°C. High-performance liquid chromatography analysis of this fraction confirmed an increase from 3.0 to 11.3% of saturated TAG and their association with part of the 1,3-stearoyl-2-oleoylglycerol preferentially to 1-palmitoyl-2-oleoyl-3-stearoylglycerol and (1,3-palmitoyl-2-oleoylglycerol).     

Effect of the addition of hardfats on the physical properties of cocoa butter

Fully hydrogenated oils, also known as hardfats, are currently employed in a limited number of applications in the food and chemical industries. The use of these compounds has been proposed for the improvement or standardization of the physical properties of lipid systems, showing great potential for use in the production of chocolate, confectionery, and similar products. This work evaluated the addition of different hardfats on the physicochemical properties of cocoa butter (CB). Fully hydrogenated oils with significantly different chemical composition, obtained from palm kernel oil (FHPKO), palm oil (FHPO), cottonseed oil (FHCO), soybean oil (FHSO), and crambe oil (FHCrO), were evaluated for their fatty acid and triacylglycerol compositions. Blends of CB/hardfats, at concentrations of 1, 3, and 5% w/w were studied by determining the melting point, solid fat profiles, microstructure, and consistency. Hardfats FHPO, FHCO, FHSO e FHCrO proved to be effective additives to modulate the physical properties of CB. Major changes on the physical properties of CB were performed by the FHSO. FHPKO was found unsatisfactory as a modifier of the CB. Practical applications : The use of hardfats as crystallization additives in products containing CB is here recommended for technological adjustments of CB formulations in relation to attributes like heat resistance and hardness, often necessary when commercialized in regions of warm climates or with large variation in temperature. The hardfats may act as potential modulators of CB crystallization, aiming to obtain higher quality products and significant cost reduction of industrial processing.     

Polymorphic transitions of cocoa butter affected by high hydrostatic pressure and sucrose polyesters

Form V to Form VI transitions of cocoa butter (CB) were investigated by varying the temperature between 28 and 21°C during storage. High hydrostatic pressure (HHP) treatments of CB melt at 60 or 21°C did not affect the rate of Form V to Form VI transitions in CB crystallized in Form V during temperature fluctuations. The HHP treatments with 100, 300, or 600 MPa of CB crystallized in Form V crystals did not alter the rate of Form V to Form VI transitions of CB. The addition of sucrose polyesters to CB melts altered the rate of Form V to Form VI transitions of CB and was dependent on the FA chain lengths and hydrophilelipophile balance (HLB) values of the SPE. The addition of most SPE to CB melts promoted the polymorphic transitions; however, sucrose polyester S-170 containing FA of chain length similar to CB with small HLB values inhibited Form V to Form VI transitions of CB for 10 temperature fluctuation cycles. Therefore, HHP treatments can be applied to foods containing high fat with little effect on the polymorphic transitions, and selected SPE may be used to retard adverse polymorphic transitions.     

Dynamic crystallization of cocoa butter. I. characterization of simple lipids in rapid- and slow-nucleating cocoa butters and their seed crystals

Six cocoa butters with different crystallization induction times and their seed crystals were analyzed for simple lipid composition. The rapid-nucleating cocoa butter samples had higher concentrations of 1-palmitoyl-2-oleoyl-3-stearoylglycerol and 1,3-stearoyl-2-oleoylglycerol (SOS), and lower concentrations of the diunsaturated triacylglycerols, 1-palmitoyl-2,3-oleoylglycerol and 1-stearoyl-2,3-oleoylglycerol, as well as higher stearic acid concentrations within their diacylglycerol fractions when compared to the slow-nucleating samples. At the early stages of crystallization, under agitation conditions at 26.5°C, cocoa butters solidified into two fractions, high-melting and low-melting. The low-melting fractions were composed of polymorphs IV and V of cocoa butter, as indicated by the onset melting temperatures of the endotherms from differential scanning calorimetry. The high-melting fractions, which had wide melting ranges, had peak maxima of 38.5–52.2°C. Seed crystals isolated at the early stage of crystallization were characterized by high concentrations of complex lipids, saturated triacylglycerols, saturated fatty acid-rich diacylglycerols, and monoacylglycerols. The rapid-nucleating seed crystals had higher concentrations of SOS when compared to their respective cocoa butters. The slow-nucleating seed crystals did not exhibit this characteristic.     

Synthesis of cocoa butter equivalent by lipase-catalyzed interesterification in supercritical carbon dioxide

With supercritical carbon dixoide as a reaction medium, the syntheses of cocoa butter equivalent by interesterification with various lipases were investigated. The study showed that among those five lipases tested, lipase IM-20 from Mucor miehei was the most effective and specific in synthesizing this cocoa butter equivalent product by interesterification. The yields of cocoa butter equivalent are affected by pressure, substrate oil composition, solubility and co-solvent. The best reaction conditions were: reaction pressure at 1500 psi, triglyceride with high content of POP (P, palmitate; O, oleate) and POO, reaction medium with 5.0% water, and reaction temperature at 50°C. The major component of cocoa butter, POS (S, stearate), can be increased by 6.0% by adding a small amount of carbon dioxide. The yield and melting point of the purified cocoa butter equivalent are 53.0% and 34.3°C, respectively.     

Production of cocoa butter substitutes <Emphasis Type="Italic">via</Emphasis> two-stage static fractionation of palm kernel oil

As are traditional fractionation technologies, static dry fractionation is a highly reliable technology for the consistent production of good-quality palm kernel stearin (PKS) for use as cocoa butter substitute (CBS) after total hydrogenation. A new process route now permits the production of unhardened yet high-quality CBS. Also an increase in total stearin yield can be achieved, via a successful refractionation of palm kernel olein. DSC analysis together with pilot static fractionation trials on the palm kernel olein indicates that a cooling water temperature that is too low (e.g., 17°C) may result in the quick formation of unstable crystals that are possibly later converted to a more stable form. The resulting mixture of crystals with a possibly different polymorphic structure is easily squeezed through the filter cloth during filtration, whereas a slower, but more homogeneous co-crystallization occurs at higher temperature (18°C or higher) and results in a much more stress-resistant slurry. Polarized light microscopy analysis confirmed that crystal size is not the only determining factor for a successful filtration. The total two-stage static fractionation of palm kernel oil (PKO) [iodine value (IV) 18] on a pilot scale results in the following three end products: PKS IV 5 (yield: 29%, for direct use as CBS), PK olein IV 27 (yield: 58%), and PKS IV 7 (yield: 13% for use as CBS after full hydrogenation). The unhardened PKS IV 5 has outstanding melting and crystallization properties, comparable to traditional hydrogenated stearin fractions. Therefore, rather than the higher stearin yield, the reduced hydrogenation capacity is most probably the most important benefit of the two-stage static fractionation process.     

Rheometry and polymorphism of cocoa butter during crystallization under static and stirring conditions

In this work the association between polymorphism and the crystal network structure developed by the TAG of cocoa butter (CB) was investigated under static and stirring crystallization conditions using a dynamic mechanical spectrometer. The results obtained showed that parameters obtained through oscillatory rheometry (i.e., phase shift angle, δ) followed the polymorphism of CB during static crystallization. Although standard DSC was not capable of differentiating the α to β′ phase transformation from the direct β′ crystallization from CB melt, δ rheograms measured these two processes separately. Additionally, through oscillatory rheometry, we followed the dimensionality of the crystal network during CB crystallization. Within this context, the pre-exponential term (In γ) from the weak-link regime equation for colloidal dispersions was much more sensitive than the fractal dimension (D) to differences in crystal size, spatial distribution of the crystal network, and melting temperature of the β′ phase of CB. On the other hand, torque measurements obtained during CB crystallization under stirring conditions showed a shear rate effect that favored TAG development in the β phase at temperatures of 19, 22, and 26.5°C, particularly at shear rates of 120 and 400 rpm. In contrast, under static conditions CB did not develop in the β phase at any of the crystallization temperatures investigated (i.e., 18 to 26.5°C).