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EAT 1.1/FS&FF 1: Confectionery Fats, Cocoa Butter, and Related Topics on Crystallization

Chair(s): N. Widlak, ADM Cocoa, USA; R. Campos, Mars Chocolate North America, USA; and D. Rousseau, Ryerson University, Canada

The Effect of Pressure and Volume on Fat Phase Behavior: Important But Often Overlooked System Variables. R.W. Lencki, R.J. Craven, University of Guelph, Guelph, ON, Canada

A large body of scientific knowledge currently exists on the crystallization behavior of triacylglycerols (TAGs). Systems range in composition from highly-purified synthetic compounds to complex multicomponent natural fats. A typical phase diagram displays melting behavior as a function of composition and temperature, and assumes minimal contributions from pressure and volume since neither variable is measured or controlled. While this approach may be appropriate for many TAG systems, there are situations where pressure and volume may play a significant role in fat crystallization (e.g. measuring the porosity of chocolate with pressurized mercury, compression and rarefaction in ultrasound). Pressure and volume can also be a factor at high solids concentrations once a fat crystal network has formed within the sample, a situation that is commonly found in many fat systems. Under these conditions, the solid matrix can constrain the volume of the occluded liquid phase, leading to internal pressures that can, at least transiently, be significantly different from the surrounding atmosphere. In this work, thermodynamic equations developed to characterize the effect of pressure and volume on TAG solid-liquid equilibrium will be used to explain a number of industrially important fat crystallization phenomena.

Early-stage Crystallization of Cocoa Butter Influenced by Different Emulsifiers. P Podchong¹, S Sonwai¹, D Rousseau², ¹Department of Food Technology, Faculty of Engineering and Industrial Technology, Silpakorn University, Thailand, ²Department of Chemistry and Biology, Ryerson University, Toronto, Canada

The purpose of this research was to investigate the early-stage crystallization kinetics, microstructure and polymorphism of cocoa butter (CB) in the presence of 5 wt% sorbitan esters (trioleate, monoleate, tristearate, monostearate or monopalmitate) or canola oil. Microstructure was investigated via polarized light microscopy, crystallization kinetics with pulsed NMR and DSC and polymorphism with simultaneous SWAXS/DSC (Hecus S3-MicrocaliX). Sorbitan tristearate had the largest effect on CB early-stage crystallization, likely co-crystallizing with POS and SOS and accelerating its initial crystallization, but retarding its crystal growth and polymorphic transformations. This was presumably due to the molecular complementarity of the stearic acids present in the CB and surfactant. There was a lesser, though still notable, influence of both sorbitan monostearate and monopalmitate whereas sorbitan trioleate and monoleate as well as canola oil had little effect given their liquid state at all temperatures. The palmitic and stearic-based surfactants reduced CB crystal size with these same surfactants accelerating initial crystallization rate (or nucleation), but leading to lower equilibrium SFCs. DSC revealed that these surfactants primarily modified the crystallization of CB’s high-melting fraction. Overall, it was shown that sorbitan esters can significantly impact cocoa butter crystallization, though this is highly-dependent on surfactant structure.

Surfactant Complementarity and Confined Gap Shear to Control Triglyceride Crystallization and Microstructure in Oil-Continuous Systems. S. Ghosh^1,2, D. Rousseau², ¹University of Saskatchewan, Saskatoon, Saskatchewan, Canada, ²Ryerson University, Toronto, Ontario, Canada

Confined gap cooling was used to generate novel lipid microstructures and water droplet encapsulation matrices. Hydrogenated canola oil (HCO) in canola oil with or without the presence of surfactants [glycerol monooleate (GMO), polyglycerol polyricinoleate (PGPR)] was cooled from 70º to 25°C at a constant shear rate (400 s^-1) in the parallel plate geometry (500 µm gap) of a controlled-shear rheometer. Different-sized and shaped HCO crystal aggregates were observed depending on the distance from the parallel plate centreline. The lowest linear shear velocity (nearest the centerline) promoted spherulite-spherulite clustering into spheroidal aggregated masses with rough surfaces ~150 μm in length. Under mid and high-shear conditions, crystal-crystal clustering was observed around a central spherulite. The resulting spheroids had a smoothened surface and became smaller with gradually higher shear (down to ~40 μm in length at high shear). Freshly-prepared 20 wt% water-in-oil emulsions consisting of the same oil phases as above and cooled under the same shear/temperature conditions were tested for their capacity to encapsulate the dispersed phase. HCO crystal spheroids made with GMO-stabilized emulsions encapsulated nearly all dispersed water droplets whereas with PGPR-stabilized emulsions, no droplets were incorporated as all droplets remained in the continuous oil phase. Comparative bulk-cooling with an impeller-type mixer did not lead to the development of such microstructures nor any water droplet encapsulation. This demonstrated the vital requirement of a confined gap for the development of these shear-induced microstructures.

Influence of Cocoa Butter Diacylglycerols on the Isothermal Crystallization of Cocoa Butter. Nathalie De Clercq¹, Sabine Danthine², Koen Dewettinck¹, ¹Ghent University, Ghent, Belgium, ²Université Gembloux Liege, Gembloux, Belgium

In this study a multi-methodological approach was used to study the isothermal crystallization, of cocoa butter in the presence of maximum 10% cocoa butter diacylglycerols over a period of four hours. At an isothermal temperature of 20°C, CB crystallizes in a two-step process: the α crystals formed during the first step transform to β' in the second step. DSC, pNMR, oscillatory rheology, XRD and PLM were used for this purpose.

Influence of Monopalmitin on the Crystallization Behaviour of Palm Oil. Stefanie Verstringe¹, Sabine Dhantine², Frédéric Depypere¹, Veerle De Graef¹, Koen Dewettinck¹, ¹Ghent University, Ghent, Belgium, ²University of Liege, Gembloux, Belgium

Emulsifiers, present by nature or added on purpose, are known to affect the crystallization and thus also the macroscopic properties of fats. Effects on all crystallization levels (nucleation, crystal growth, polymorphic transitions, network formation, sintering) as well as on fat crystal size and morphology are reported. However, research on the influence of emulsifiers on the crystal size and crystal morphology, microstructural development and macroscopic properties of crystallized fat systems is still in its infancy. Therefore, a multi-methodological analytical approach was used in this research to gain more insight into the effect of monopalmitin on the palm oil crystallization behaviour. The blends were crystallized at different temperatures ranging from 15 to 28°C. pNMR and DSC were applied to characterize the primary crystallization behaviour. Next to primary crystallization, microstructural development and macroscopic properties were evaluated by oscillatory rheology. Polarized light microscopy was used to follow the development of the fat crystal networks. XRD measurements were used to elucidate the polymorphic behaviour of the blends. From the results, it can be concluded that a monopalmitin concentration as low as 1% already has a clear effect on the palm oil crystallization behaviour.

Characterization by Rheo-NMR and Modeling of a Crystallizing Triglyceride Mixture. M. Li, G. Mazzanti, Dalhousie University, Halifax, NS, Canada

Shear flow affects the solid content (SC) and nanoparticle size of fats. Binary mixtures of pure Trialurin and Trimyristin in a ratio of 7:3 were diluted to 60% in non-crystallizing Triolein. 40%7L3M was cooled at 10°C/min from the melt at 60°C down to several temperatures between 12°C and 24°C. The samples were crystallized at each temperature either statically or under shear rates of 800, 80, and 8s^-1. The sample cell combined a rheometer with a nuclear magnetic resonance (NMR) spectrometer to measure SC values. Viscosity and total mechanical energy delivered were precisely measured by the rheometer. The measurements were compared to common equations describe the dependency of viscosity on solid volume fraction, to understand the effect of orientation of the crystallites at higher shear rates. Most of the results were described accurately by the Arvami model whereas in some of them the presence of two regimes was observed, where diffusion controlled growth dominated the later times. The small values of the intrinsic viscosity were observed at high shear rate showing that the particles were small in size compare to low shear rate, which supports the hypothesis that shear reduces the particle size.

Rheo-NMR Study of the Structural Consequences of Shear Variation during the Crystallization of Milk Fat. G. Mazzanti^1,2, ¹Dalhousie University, Halifax, NS, Canada, ²Institute for Research in Materials, Halifax, NS, Canada

The effect of shear variations on the crystallization of milk fat was investigated using Rheo-NMR. Previous Rheo-XRD experiments had demonstrated that the variation in applied shear rate during crystallization had modified the size of the final nanoplatelets in different fats (G. Mazzanti et al., Cryst. Growth Des., 11 (10), 4544–4550). To further investigate the structural consequences of this size modification, milk fat samples were crystallized under two continuous and two discontinuous shear profiles, at a common temperature. The crystallizing colloidal suspensions displayed a shear thinning time-dependent rheological behavior, consistent with the expected. The final solid fraction was affected by the type of shear profile applied. It was correlated to the Rheo-XRD integrated intensity values, demonstrating the effect on the proportionality factors that nanopolatelet aggregation/segregation and orientation have under shear. At the end of the shear profile the structures were allowed to set and were monitored during a short period of time using oscillatory Rheo-NMR. The four profiles resulted in different visco-elastic time-profiles of the materials. These properties were consistent with the modification of solid content and the Rheo-XRD observations of nanoplatelets size change.

Use of Time-resolved X-ray Diffraction to Monitor the Difference in Phase Transformation Trajectories of Tags Containing Oleic and Stearic Acids, as a Function of Symmetry and Cooling Rate. Laziz Bouzidi, Suresh S. Narine, Trent Centre for Biomaterials Research, Departments of Physics & Astronomy and Chemistry, Trent University, Peterborough, Ontario K9J 7B8, Canada

The thermal and polymorphic evolutions associated with crystallization of pure triacylglycerols (TAGs) with Oleic and Stearic Fatty Acids were monitored using a laboratory X Ray Diffractometer, allowing time-resolved X-ray diffraction at both wide and relatively small angles as a function of temperature (XRDT). These measurements were performed in combination with high sensitivity differential scanning calorimetry (DSC) carried out at two widely different cooling rates in the −90 to +90°C range. It was found that the combination of these techniques allowed the thermal monitoring of TAG polymorphism even at relatively high cooling rates of 3°C/min. The formation of α, β′ and β phases, and their transitions were followed simultaneously by DSC and XRDT, facilitating the identification of the thermal events recorded. The large influence of molecular symmetry on crystallization and evolution of polymorphism of TAGs with Oleic and Stearic Fatty Acids was demonstrated, and has significant implications for the crystallization of cocoa butters sourced from different geographies and altitudes with varying TAG symmetries involving oleic and stearic acids.

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