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1.
The kinetics of isothermal crystallization of binary mixtures of cocoa butter with milk fat and milk fat fractions were evaluated
by applying the Avrami equation. Application of the Avrami equation to isothermal crystallization of the fats and the binary
fat blends revealed different nucleation and growth mechanisms for the fats, based on the Avrami exponent. The suggested mechanism
for cocoa butter crystallization was heterogeneous nucleation and spherulitic growth from sporadic nuclei. For milk fat, the
mechanism was instantaneous heterogeneous nucleation followed by spherulitic growth. For milk fat fractions, the mechanism
was high nucleation rate at the beginning of crystallization, which decreased with time, and plate-like growth. Addition of
milk fat fractions did not cause a significant change in the suggested nucleation and growth mechanism of cocoa butter. 相似文献
2.
Stefan Bolliger Yuantong Zeng Erich J. Windhab 《Journal of the American Oil Chemists' Society》1999,76(6):659-667
In the present work cocoa butter and chocolate were precrystallized by means of a newly developed shear crystallizer. The
shear crystallizer was integrated into a circular loop. The handling of precrystallized cocoa butter showed a high dependency
on the timing of applied analysis. Differential scanning calorimetry, calorimetry, rheometry, and in-line near-infrared (NIR)
were all directly influenced by the fat crystal structure. Nevertheless, for cocoa butter it was shown that mechanical energy
input (rpm) had a significant influence on viscosity, melting enthalpy, and slope at the second point of inflection of a temper
curve. Experiments with cocoa butter at constant exit temperature showed a linear increase of viscosity between 0.1 and 0.8
Pa·s in the range of 300 to 1300 rpm. Melting enthalpy increased in the same rpm interval from 0.02 to 2.5 J/g. Solidification
time (from 4.5 to 0.5 min) and slope (from 0.82 to 0.15, second point of inflection of temper curve) consequently decreased
(both with exponential approximation). For cocoa butter, slope and solidification time correlated linearly whereas solidification
time and viscosity followed a power law fit. This proved that defined relationships exist between rheological data and data
from temper curve measurements. Viscosity was linearly dependent on crystal content. By means of NIR spectroscopy good correlation
models for cocoa butter viscosity, enthalpy (crystal content), and slope values were found. For precrystallized chocolate,
analytical values such as viscosity and slope values were detected off-line and used for calibration of NIR spectroscopy. 相似文献
3.
S. Padar S. A. K. Jeelani E. J. Windhab 《Journal of the American Oil Chemists' Society》2008,85(12):1115-1126
Isothermal crystallization kinetics of unseeded and seeded cocoa butter and milk chocolate is experimentally investigated
under quiescent conditions at different temperatures in terms of the temporal increase in the solid fat content. The theoretical
equations of Avrami based on one-, two- and three-dimensional crystal growth are tested with the experimental data. The equation
for one-dimensional crystal growth represents well the kinetics of unseeded cocoa butter crystallization of form α and β′.
This is also true for cocoa butter crystal seeded milk chocolate. The sterical hindrance due to high solids content in chocolate
restricts crystallization to lineal growth. In contrast, the equation for two-dimensional crystal growth fits best the seeded
cocoa butter crystallization kinetics. However, a transition from three- to one-dimensional growth kinetics seems to occur.
Published data on crystallization of a single component involving spherulite crystals are represented well by Avrami’s three-dimensional
theoretical equation. The theoretical equations enable the determination of the fundamental crystallization parameters such
as the probability of nucleation and the number density of nuclei based on the measured crystal growth rate. This is not possible
with Avrami’s approximate equation although it fits the experimental data well. The crystallization can be reasonably well
defined for single component systems. However, there is no model which fits the multicomponent crystallization processes as
observed in fat systems. 相似文献
4.
Paige A. Palmieri Richard W. Hartel 《Journal of the American Oil Chemists' Society》2019,96(8):911-926
Cocoa powder quality is determined by its color, flavor, dispersion, and flow properties, which can be controlled via tempering. Design of a cocoa powder tempering profile, however, requires that the mechanism of cocoa butter crystallization in cocoa powder be fully understood. Low-fat (8–12%) and high-fat (20–24%) cocoas were sourced from two commercial manufacturers at varying degrees of alkalization and compared with two commercial cocoa butters. Unrefined paired cocoa powders and cocoa butters sampled from the hydraulic press were also evaluated. Isothermal crystallization kinetics and polymorphism of cocoa powders and cocoa butters were compared at 18, 21, and 24 °C using a direct time-domain nuclear magnetic resonance method, differential scanning calorimetry, and x-ray diffraction. Crystallization was also studied under dynamic tumbling conditions. It was found that cocoa butter in cocoa powder was nucleated by the cocoa powder matrix and transitioned to higher-stability polymorphs more rapidly than bulk cocoa butters. High-fat cocoas also exhibited enhanced crystallization kinetics relative to low-fat cocoas, showing that differences in the cocoa microstructure may influence crystallization behavior. Notably, alkalization did not significantly affect the crystallization behavior of most cocoa powders. Finally, it was found that tumbling conditions led to crystallization of βV and that caking, especially of high-fat cocoas, could be reduced by a static low-temperature hold step prior to tumbling. Overall, these results demonstrated that crystallization of cocoa butter in cocoa powder is influenced both by the intrinsic attributes of the cocoa powder as well as the conditions of the tempering process. 相似文献
5.
Kees van Malssen René Peschar Henk Schenk 《Journal of the American Oil Chemists' Society》1996,73(10):1209-1215
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. 相似文献
6.
Scott A. Hindle Malcolm J. W. Povey Kevin W. Smith 《Journal of the American Oil Chemists' Society》2002,79(10):993-1002
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. 相似文献
7.
Binary mixtures of cocoa butter and lauric fats have widespread use in chocolates and confections, yet incompatibilities between these fats can present formulation and processing constraints. This study examined the phase behavior and crystallization kinetics of cocoa butter-lauric fat model systems and chocolate-lauric fat blends. Solid fat content (SFC) profiles and isosolid diagrams confirmed eutectic and diluent interactions, indicating a softening of cocoa butter by lauric fat addition. Crystallization kinetics of model systems adhered to an exponential growth model. High lauric fat levels delayed crystal growth and reduced equilibrium SFC of cocoa butter. Coconut and palm kernel oils altered the solidification mechanisms of cocoa butter to a greater extent than fractionated palm kernel oil. Chocolate systems displayed multi-step crystal growth that contrasted with the exponential growth observed in the model systems. At high lauric fat levels (30%), crystallization onset was significantly lengthened. Blends with high lauric fat contents showed low \(G_{{\text {max}} }^{\prime }\) and did not achieve final equilibrium after 60 min of cooling, indicating incomplete crystallization. 相似文献
8.
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). 相似文献
9.
After an induction period, crystallization of cocoa butter under dynamic conditions at 26.5°C occurs in two stages, primary
and secondary. The primary stage involves nucleation, crystal growth, aggregation, and sintering. Crystals formed during the
primary stage were slightly or non-birefringent, and had long, irregular-shaped filaments. The secondary stage was initiated
by the formation of spherulites. Total crystallization time may depend upon the crystal growth rate in the primary stage and
the time that coca butters take to form the spherulitic crystals in the secondary stage. After the spherulitic crystals formed,
the crystal growth rates were rapid. Cocoa butters crystallized into two fractions during the primary and secondary stages.
The low-melting fractions had onset melting temperatures similar to those of polymorphs IV and V of cocoa butter. The high-melting
fractions, which were observed at the latter stages of crystallization, had differential scanning calorimetry endotherms with
peak maxima at approximately 34–36°C (Form VI). The concentrations of 1,3-stearoyl-2-oleoylglycerol (SOS) in the crystals
during growth were higher than those in the original cocoa butter. As crystallization progressed, crystals increased in their
proportions of SOS in the triacylglycerol fraction. Concentrations of the C18 free fatty acids were lower during early crystallization as compared to the original cocoa butter. 相似文献
10.
Seed crystals isolated from Ivory Coast cocoa butter were shown to differ in chemical and thermal characteristics from solidified
Ivory Coast butter. Higher concentrations of complex lipids in the seed crystals have led to speculation on the role these
polar molecules play in lipid crystallization events. Phospholipids separated from lipid seed crystal isolates were twelve-fold
more concentrated than the original cocoa butter. Seed crystals contained 3.99% phospholipids while cocoa butter samples contained
0.34%. Phosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, lysophosphatidylcholine,
phosphatidylserine, and phosphatidic acid were identified in cocoa butter with phosphatidylcholine (37.7%), phosphatidylglycerol
(27.3%) and phosphatidyl-ethanolamine (15.6%) being the major phospholipid constituents. Two phospholipids not previously
reported in cocoa butter were identified as phosphatidylglycerol and diphosphatidylglycerol based on co-migration of standards.
Cocoa butter and its seed crystals contained the same phospholipid entities; however, individual phospholipids differed significantly
in concentration. Phosphatidylethanolamine (30.4%) and phosphatidylcholine (30.2%) were the major phospholipids in seed crystal
samples. Fatty acid composition of cocoa butter and seed crystal phospholipids were found to be similar, with the exception
of myristic, stearic and oleic acids. Myristic acid was three-fold higher in phosphatidylglycerol and phosphatidylethanolamine
in the seed crystals, whereas stearic acid was significantly lower in the seed crystals when compared to the cocoa butter.
Concentrations of oleic acid were twice as high in seed crystal phosphatidylethanol-amine and almost four times as high in
seed crystal phosphatidylcholine than in corresponding cocoa butter samples. The possible role phospholipids play in seed
crystal development and in crystallization events is discussed. 相似文献
11.
As a first approach to modeling the crystallization behavior of cocoa butter, the binary system of its two major components,
1-palmitoyl-2-oleoyl-3-stearoyl-s n-glycerol (POS) and 1,3-distearoyl-2-oleoyl-s n-glycerol (SOS), was studied. Differential scanning calorimetry, coupled with polarized light microscopy, was used to determine
the phase diagrams of the various polymorphic forms (the most metastable sub-α and α, intermediate δ and β′, and stable β).
Associated theoretical phase diagrams were also built. The presence of a solid solution for β and the ideal behavior of α
were confirmed. Kinetics of isothermal solidification as a function of temperature were studied for three compositions of
the POS-SOS system. Results were displayed as time-temperature-transformation (TTT) diagrams and crystal morphology maps.
Dependence of the crystallization kinetics on composition of the binary system was interpreted in terms of nucleation and
growth mechanisms. The asymmetry of the POS molecule induces a slower growth rate of the mixture when the concentration of
this triacylglycerol is increased. Solidification kinetics during continuous cooling were studied at various cooling rates
for the system POS-SOS 25:75. Experimental results were compared with numerical predictions of a solidification model based
upon TTT data and an additivity principle. The calculated and measured volume fractions of the different phases formed and
times of onset and finish of the solidification were in good agreement. 相似文献
12.
Seed crystals which formed during early stages of cocoa butter solidification have been isolated and determined to have extremely
high melting points. The melting points of the seed crystals generally exceeded 60°C, in contrast to cocoa butter, which melts
between 30–35°C. In addition, the melting point of the seed crystals decreased as a function of crystal growth time. Evidence
suggests that the high-melting seed crystal is not an additional polymorphic form of cocoa butter, but rather a distinct crystalline
entity. Consequently, a unique compositional make-up is suspected as being responsible for the elevated melting point. A technique
to separate seed crystals from the molten cocoa butter mass has been developed. The procedure has been shown not to alter
the thermal and compositional properties of the isolated seed crystals. 相似文献
13.
Iwao Hachiya Tetsuo Koyano Kiyotaka Sato 《Journal of the American Oil Chemists' Society》1989,66(12):1757-1762
Effects of seeding of fat crystals on the crystallization kinetics of cocoa butter and dark chocolate were examined with a
rotational viscometer. The seed crystals employed were cocoa butter, 1,3-distearoyl-2-oleoylglycerol (SOS), 1,3-dibehenoyl-2-oleoylglycerol
(BOB) and 1,2,3-tristearoylglycerol (SSS). The seed powders were prepared by pulverization below —50°C, the dimensions being
in a range from 20–70 μm. Particular attention was paid to the influence of polymorphism of the seed crystal. We found that
all of the above seed materials accelerated the crystallization, the degree of acceleration being in a following order; SOS
(β
1) > cocoa butter (Form V) > SOS (a mixture ofβ’ andβ
2) > BOB (β
2) > BOB (pseudo-β’) > SSS (β). Precise measurements of the crystallization kinetics showed that the most influential factors in the seeding
effects are the physical properties of the seed materials—above all, thermodynamic stability, and similarity in the crystal
structure to cocoa butter are the most determinative. 相似文献
14.
José Vila Ayala Gijs Calliauw Imogen Foubert Koen Dewettinck Bill Dyer Wim De Greyt 《Journal of the American Oil Chemists' Society》2007,84(11):1069-1077
Natural and alkalized cocoa butters were bleached and subsequently steam refined in a continuous packed column at temperatures
ranging between 160 and 220 °C. None of the processes evaluated gave rise to any detectable formation of trans fatty acids, interesterification or polymerization. For the pressures and steam injection rates used, packed-column steam
refining required a minimum temperature of 170 °C to achieve acceptable taste. Bleaching was highly effective in preventing
darkening at high steam-refining temperatures, as well as in removing alkaloids, such as theobromine and caffeine, before
steam refining. The impacts on the crystallization properties of cocoa butter were studied using DSC and P-NMR. The more significant
changes in crystallization kinetics and equilibrium values can be reliably predicted on the basis of FFA removal from the
butter. 相似文献
15.
Werner Landmann N. V. Lovegren R. O. Feuge 《Journal of the American Oil Chemists' Society》1961,38(9):466-469
Several cocoa butter-like fats, which had been prepared by fractional crystallization of the reaction product obtained on interesterifying highly-hydrogenated cottonseed oil and a triolein product or olive oil, were characterized and compared with cocoa butter. The fats, as obtained by fractional crystallization from acetone solutions, contained varying amounts of glycerides melting above 37°C., an undesirable feature which caused the fats to thicken too much when used in chocolate type compositions under the same conditions employed with cocoa butter. The higher-melting glycerides could be removed by filtration, or their proportions could be decreased by changing the fractionation temperatures. The fats melted mostly over the same temperature range associated with cocoa butter, and the best of the fats resembled cocoa butter closely over the temperature range 0° to 30°C. The cocoa butter-like fats resembled cocoa butter in hardness at all test temperatures. The fats were reasonably compatible with cocoa butter, that is, in mixtures of the two, one did not cause extensive premelting of the other. According to their cooling curves, the cocoa butter-like fats did not supercool as cocoa butter does. The former contain not only the 2-oleodisaturated glycerides of cocoa butter but also positional isomers of these glycerides. When the fats were molded under the same conditions employed with cocoa butter, linear shrinkage was only about one-third that of cocoa butter. 相似文献
16.
Miguel A. Bootello Rafael Garcés Enrique Martínez-Force Joaquín J. Salas 《Journal of the American Oil Chemists' Society》2011,88(10):1511-1519
Fractionation of fats and oils makes it possible to generate products with specific properties from natural fats that contain
a variety of triacylglycerol (TAG) species. High-oleic high-stearic (HOHS) sunflower oils contain high levels of saturated
fatty acids, mainly stearate, on a high-oleic background. Accordingly, HOHS oils could be a source of disaturated TAGs appropriate
for cocoa butter equivalent formulations. We examined the kinetics of HOHS oil crystallization, paying special attention to
the influence of crystal seeding and temperature on the process and the composition of the final fractions. This oil was fractionated
at 18 °C, and seeding increased the amount of disaturated TAGs recovered in the precipitate from 23% to up to 30%. The experimental
data collected were fitted using the models of Gompertz and Avrami to study how well these models fitted the data and their
utility in predicting the progress of crystallization. At seeding additions above 0.25% there was a change in the crystallization
mechanism that improved the process of fractionation. The effect of temperature was also studied, showing important increases
in the maximum rates of crystallization when fractionations were carried out at lower temperatures. Finally, the melting profiles
of the fractions enriched in saturated fatty acids were studied, showing amounts of solids intermediate between the initial
oil and cocoa butter. 相似文献
17.
Arjen van Langevelde René Driessen Wim Molleman René Peschar Henk Schenk 《Journal of the American Oil Chemists' Society》2001,78(9):911-918
Depending on the maximum temperature before cooling, cocoa butter recrystallizes in the β(V) and/or β(VI) phase. In order to obtain structural information on the seed material initiating this recrystallization process, experiments with cocoa butter were performed at a small-angle X-ray scattering station. Crystallization of cocoa butter at various crystallization temperatures provided long d-spacing values (d>45 Å) that can be attributed to the polymorphic phases. From the recrystallization experiments it is concluded that the seeds initiating rapidstarting recrystallization have an 1,3-distearoyl-2-oleoylglycerol-dominated triple chain-length packing. Furthermore, the β(VI) phase of cocoa butter seems to adopt a similar packing. The seed crystals that initiate the slow-starting recrystallization and result in the β(V) phase are likely to be different from those giving the β(VI) phase. 相似文献
18.
D. Rousseau S. M. Hodge M. T. Nickerson A. T. Paulson 《Journal of the American Oil Chemists' Society》2005,82(1):7-12
Hydrogenated cottonseed oil (HCSO) is commonly used as a β′-stable fat in margarines and shortenings. In the present study,
the crystallization behavior of HCSO is altered via dilution, agitation, tempering regime, and the addition of an emulsifier [polyglycerol polyricinoleate (PgPr)]. Key properties
assessed include crystal morphology (with polarized light microscopy), polymorphic behavior (with X-ray diffraction), and
crystallization kinetics (with DSC). It is demonstrated that on considerable dilution with canola oil (4% w/w), HCSO can be
crystallized in the β′ or β polymorph with associated changes in crystal morphology, depending on tempering regime. Crystallization
from the melt to 25°C results in the β′-form, as there is insufficient supercooling to form the β polymorph but enough to
form the metastable β′. With cooling from the melt to 5°C, there is adequate supercooling for the δ polymorph to form, with
the presence of the canola oil facilitating the transformation toward this stable phase. Static vs. crystallization under
agitation does not lead to visible changes in either polymorphic behavior or crystal morphology. However, there is extensive
secondary nucleation and growth as a result of crystals breaking off accreting agglomerates. The presence of PgPr, added as
a crystal modifier, does not affect the final crystal polymorph or morphology, except under one set of conditions—crystallization
from the melt to 5°C with agitation, whereby it considerably alters crystallization behavior. 相似文献
19.
Effects of ultrasonic irradiation on crystallization behavior of tripalmitoylglycerol and cocoa butter 总被引:2,自引:2,他引:0
Kaoru Higaki Satoru Ueno Tetsuo Koyano Kiyotaka Sato 《Journal of the American Oil Chemists' Society》2001,78(5):513-518
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. 相似文献
20.
A new monitoring device for the nonisothermal crystallization of thermoplastic polymers, polyethylene, polypropylene, polystyrene, and polyamide, is developed utilizing a quartz crystal resonator, and its performance is evaluated by comparing the measurements with the results of DSC thermoanalysis and microscopic observation. The experimental results of four different polymers indicate that the variation of resonant freency of the quartz crystal resonator is a good means to monitor the crystallization process. Though the measurements of melting and crystallization are close to the DSC outcome, more deviation is observed with the new device. The change in crystalline morphology during the crystallization process is also detected from the slope changes of the frequency decrease. In comparison with the microscopic observation of polymer films, it is found that the processes of nucleation and crystal growth in nonisothermal crystallization can be explained with the variation of the resonant frequency of the quartz crystal resonator. In addition, crystallization kinetics is modeled with the Avrami equation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献