The effect of shear on the crystallization of cocoa butter

Abstract

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.Cocoa butter (CB) is a semisolid fat that exhibits brittleness below 20°C, begins to soften in the region of 28-32°C, and melts completely below body temperature (1). CB is predominantly composed of three monounsaturated TAG-POP, POS and SOS (where P = palmitate, O = oleate, and S = stearate)-which make up approximately 82% of its components (2). It also contains minor concentrations of MAG, DAG, phospholipids, glycolypids, sterols, FFA, and fat-soluble vitamins. The TAG composition of CB from cocoa beans grown in different areas varies slightly according to differences in genetics, climate (temperature, rainfall, and sunlight), and agricultural practices.CB, which itself is tasteless (1), is a key ingredient in chocolate. It typically corresponds to approximately one-third of the chocolate composition. Because of this, the crystallization of CB plays an essential role in controlling the physical and thermal properties of chocolate products. The crystallization behavior of CB is, however, very complex owing to polymorphism, i.e., the ability of the fat to exist in different crystalline forms with different types of crystal packing and thermodynamic stabilities (3). It is now generally accepted that CB can exist in six polymorphs, which in order of increasing thermodynamic stability are termed Form I-Form VI (4). Only Form V is used by the confectionery industry as the optimal polymorph for CB in chocolate (5). This is because Form V is a stable polymorph with a melting range that is high enough to allow chocolate to be stored at room temperature, and low enough that chocolate becomes a smooth liquid when it is heated in the mouth. Form V provides chocolate products with snap (ability to break apart easily), good demolding p...

Blending of mango kernel fat and palm oil mid-fraction to obtain cocoa butter equivalent

“…4). At 1 h of crystallization, the diffraction pattern of the fat showed mainly the diffraction peaks of form IV (β′) with two additional peaks at 3.79 Å, 3.95 Å and a peak with low scattering intensity of form V (β) at 4.55 Å, indicating that CB had partially transformed into form V. The phase transition of CB during quiescent crystallization from forms II to IV bypassing form III (β′) has been observed before (Sonwai and Mackley 2006). The crystallization behavior of MIX was very similar to that of CB (Fig.…”

Influence of shear flow on polymorphic behavior and microstructural development during palm oil crystallization

“…This can be easily understood in terms of supercooling: The larger the supercooling (thus the lower the temperature), the higher is the driving force, and thus the earlier the crystallization will start. The increase in viscosity of the sample during crystallization can be related to an increase in the amount of fat crystals present and thus to the degree of crystallinity [10]. However, viscosity is not only a result of increasing amounts of solids present in the liquid, but is also influenced by the crystal size distribution as well as the interactions between the different crystals.…”

“…Mazzanti et al [7][8][9] used time-resolved X-ray scattering to assess the influence of various shear rates on the crystallization of palm oil (with shear ranging from 45 to 2880 s -1 ), cocoa butter, milk fat and stripped milk fat. Sonwai and Mackley [10] and MacMillan and Roberts [11] used the same technique to elucidate the effect of various shear rates on the polymorphic transitions in cocoa butter. Dhonsi and Stapley [12] and Toro-Vazquez et al [13] used a rheological approach to study cocoa butter crystallization under continuous shear, while Garbolino et al [14] equipped a rheometer with ultrasonic sensors to asses the effect of shear on crystallization of a confectionery fat.…”

“…Dhonsi and Stapley [12] and Toro-Vazquez et al [13] used a rheological approach to study cocoa butter crystallization under continuous shear, while Garbolino et al [14] equipped a rheometer with ultrasonic sensors to asses the effect of shear on crystallization of a confectionery fat. These experiments were all carried out with continuous shear throughout the whole experiment, except for the study of Sonwai and Mackley [10]. They applied a steady shear step (50-1500 s -1 ) for a short period (250 s) after which the sample was further monitored by means of a dynamic time sweep.…”

Effect of Shearing on Crystallization of Palm Oil-Based Fat Blends

“…Syringe-extrusion method In the syringe-extrusion method, a 2-mL glass syringe was filled with a mixed fat blend and held at 80℃ before cooling. For rapid cooling, the syringe filled with the fat blend was covered with iced water for 2 min, held at 5℃ for 1 h, and then sheared by extruding 1995, Mazzanti et al, 2003, Mazzanti et al, 2005, Sonwai and Mackley, 2006, De Graef et al, 2009, Tarabukina et al, 2009; however, most of the research was focused on the effect of shearing on initial crystallization behavior. Commercially distributed fat food products are required to maintain their quality over weeks to months.…”