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Title: A Conceptual Model for Shear-Induced Phase Behavior in Crystallizing Cocoa Butter

Abstract

We propose a conceptual model to explain the quantitative data from synchrotron X-ray diffraction experiments on the shear-induced phase behavior of cocoa butter, the main structural component of chocolate. We captured two-dimensional diffraction patterns from cocoa butter at crystallization temperatures of 17.5, 20.0, and 22.5 {sup o}C under shear rates from 45 to 1440 s{sup -1} and under static conditions. From the simultaneous analysis of the integrated intensity, correlation length, lamellar thickness, and crystalline orientation, we postulate a conceptual model to provide an explanation for the distribution of phases II, IV, V, and X and the kinetics of the process. As previously proposed in the literature, we assume that the crystallites grow layer upon layer of slightly different composition. The shear rate and temperature applied define these compositions. Simultaneously, the shear and temperature define the crystalline interface area available for secondary nucleation by promoting segregation and affecting the size distribution of the crystallites. The combination of these factors (composition, area, and size distribution) favors dramatically the early onset of phase V under shear and determines the proportions of phases II, IV, V, and X after the transition. The experimental observations, the methodology used, and the proposed explanation are of fundamentalmore » and industrial interest, since the structural properties of crystalline networks are determined by their microstructure and polymorphic crystalline state. Different proportions of the phases will thus result in different characteristics of the final material.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
929965
Report Number(s):
BNL-80569-2008-JA
TRN: US0806675
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Crystal Growth and Design; Journal Volume: 7; Journal Issue: 7
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; COCOA PRODUCTS; CORRELATIONS; CRYSTALLIZATION; DATA; DIFFRACTION; DISTRIBUTION; INTERFACES; FATS; KINETICS; LAYERS; LENGTH; MICROSTRUCTURE; NUCLEATION; ORIENTATION; SEGREGATION; SHEAR; SIZE; SYNCHROTRON RADIATION; THICKNESS; X-RAY DIFFRACTION; national synchrotron light source

Citation Formats

Mazzanti,G., Guthrie, S., Marangoni, A., and Idziak, S. A Conceptual Model for Shear-Induced Phase Behavior in Crystallizing Cocoa Butter. United States: N. p., 2007. Web. doi:10.1021/cg050467r.
Mazzanti,G., Guthrie, S., Marangoni, A., & Idziak, S. A Conceptual Model for Shear-Induced Phase Behavior in Crystallizing Cocoa Butter. United States. doi:10.1021/cg050467r.
Mazzanti,G., Guthrie, S., Marangoni, A., and Idziak, S. Mon . "A Conceptual Model for Shear-Induced Phase Behavior in Crystallizing Cocoa Butter". United States. doi:10.1021/cg050467r.
@article{osti_929965,
title = {A Conceptual Model for Shear-Induced Phase Behavior in Crystallizing Cocoa Butter},
author = {Mazzanti,G. and Guthrie, S. and Marangoni, A. and Idziak, S.},
abstractNote = {We propose a conceptual model to explain the quantitative data from synchrotron X-ray diffraction experiments on the shear-induced phase behavior of cocoa butter, the main structural component of chocolate. We captured two-dimensional diffraction patterns from cocoa butter at crystallization temperatures of 17.5, 20.0, and 22.5 {sup o}C under shear rates from 45 to 1440 s{sup -1} and under static conditions. From the simultaneous analysis of the integrated intensity, correlation length, lamellar thickness, and crystalline orientation, we postulate a conceptual model to provide an explanation for the distribution of phases II, IV, V, and X and the kinetics of the process. As previously proposed in the literature, we assume that the crystallites grow layer upon layer of slightly different composition. The shear rate and temperature applied define these compositions. Simultaneously, the shear and temperature define the crystalline interface area available for secondary nucleation by promoting segregation and affecting the size distribution of the crystallites. The combination of these factors (composition, area, and size distribution) favors dramatically the early onset of phase V under shear and determines the proportions of phases II, IV, V, and X after the transition. The experimental observations, the methodology used, and the proposed explanation are of fundamental and industrial interest, since the structural properties of crystalline networks are determined by their microstructure and polymorphic crystalline state. Different proportions of the phases will thus result in different characteristics of the final material.},
doi = {10.1021/cg050467r},
journal = {Crystal Growth and Design},
number = 7,
volume = 7,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • No abstract prepared.
  • Modifications of a benchtop NMR instrument were made to apply temperature control to a shearing NMR cell. This has enabled the determination in situ of the solid fat content (SFC) of cocoa butter under shearing conditions. The cocoa butter was cooled at 3 C/min to three final temperatures of 17.5, 20.0, and 22.5 C with applied shear rates between 45 and 720 s-1. Polymorphic transitions of the cocoa butter were determined using synchrotron X-ray diffraction with an identical shearing system constructed of Lexan. Sheared samples were shown to have accelerated phase transitions compared to static experiments. In experiments where formmore » V was confirmed to be the dominant polymorph, the final SFC averaged around 50%. However, when other polymorphic forms were formed, a lower SFC was measured because the final temperature was within the melting range of that polymorph and only partial crystallization happened. A shear rate of 720 s-1 delayed phase transitions, likely due to viscous heating of the sample. Pulsed NMR is an invaluable tool for determining the crystalline fraction in hydrogen containing materials, yet its use for fundamental and industrial research on fat or alkanes crystallization under shear has only recently been developed.« less
  • Polymethylmethacrylate (PMMA) spheres suspended in benzyl alcohol are found to swell to more than two times that of their dry radius and have been observed to undergo an equilibrium phase transition from liquid to crystalline structure with increasing concentration. The width of the coexistence region is found to be narrower by nearly half compared to simulation results for hard sphere systems. Comparison of the measured freezing point and fractional density change upon melting with those calculated from soft sphere simulations are consistent with a purely repulsive interparticle potential on the order of 1/r{sup 20}. Analysis of powder pattern scattering profilesmore » from samples in the crystallized region of the equilibrium phase diagram indicates crystallites made up of a registered random stacking of hexagonal close packed planes, similar to that found in monodisperse suspensions of hard spheres. With the application of oscillatory shear, nonequilibrium microstructures similar to those found in model hard sphere systems have been observed in these suspensions.« less