Cocoa butter and confectionery fats. Studies using programmed temperature X-ray diffraction and differential scanning calorimetry

Physical characterization of chocolates prepared with various soybean and milk powders physical character soybean milk chocolate

The physical characterization of chocolate products is vital in manufacturing, and the chocolate's processing time and composition directly influence physical properties, such as rheology and melting. The objective of this study was to investigate the effects of processing time and the ingredient types on the physical properties of milk chocolates containing soy milk powder and soy protein isolate. Characteristics of skimmed milk chocolate (SMC) and whole milk chocolate (WMC) were compared to soy milk chocolate and soy protein chocolate (SPC). Rheological data of chocolate products were fitted to Casson, Herschel-Bulkley, and Bingham models. The highest viscosity was observed for SPC samples, whereas yield stress was the highest for SMC samples after 2 hr of processing. The increase in milk and soy fats in the formulation softened the texture and decreased the whiteness index significantly (p < .05). PSD results show that SPC had the highest D90 (40.1 μm) and the lowest specific surface area (893 m² /kg) after 6 hr of processing. SPC samples had the narrowest particle size distribution observed by the span values. X-ray diffraction analysis showed that all the samples had the desired Form V, crystal form. The differential scanning calorimetry thermogram was used to determine phase transitions and melting behaviors. At the end of processing, melting enthalpies (ΔH_melt ) were significantly lower (p < .05) in milk chocolates.

Tailoring crystallization and physical properties of palm mid-fraction with sorbitan tristearate and sucrose stearate

This paper addresses sorbitan and sucrose ester in physical transformations of palm mid-fraction (PMF). Both emulsifiers influenced the crystallization properties of PMF, mainly due to emulsifier solubility, which affects its ability to interfere with the kinetics of solution-mediated phase transformations. DSC results corroborate the polymorphism analysis, indicating that the mechanism and rate of phase transformation depend on the chemical structure and amount of each emulsifier. The addition of sorbitan tristearate (STS) and sucrose stearate (S-370) increased the crystallization speed of the PMF and caused changes in the crystallization behavior. STS favored the β'→β transition, while S-370 stabilized the β'-form. We can conclude that the presence of emulsifiers dissimilar to the composition of PMF modified its physical structure, either by increasing the liquid fraction or by reducing molecular motion, facilitating or preventing polymorphic transformations.

Characterisation of Fat Crystal Polymorphism in Cocoa Butter by Time-Domain NMR and DSC Deconvolution

The polymorphic state of edible fats is an important quality parameter in fat research as well as in industrial applications. Nowadays, X-ray diffraction (XRD) is the most commonly used method to determine the polymorphic state. However, quantification of the different polymorphic forms present in a sample is not straightforward. Differential Scanning Calorimetry (DSC) is another method which provides information about fat crystallization processes: the different peaks in the DSC spectrum can be coupled to the melting/crystallisation of certain polymorphs. During the last decade, nuclear magnetic resonance (NMR) has been proposed as a method to determine, qualitatively and/or quantitatively, the polymorphic forms present in fat samples. In this work, DSC- and NMR-deconvolution methods were evaluated on their ability to determine the polymorphic state of cocoa butter, with XRD as a reference method. Cocoa butter was subjected to two different temperature profiles, which enforced cocoa butter crystallization in different polymorphic forms. It was found that XRD remains the best method to qualitatively determine the polymorphic state of the fat. Whereas the quantitative NMR and DSC deconvolution results were not fully in line with the XRD results in all cases, NMR deconvolution showed great promise both in a qualitative and quantitative way.

Molecular Origins of Polymorphism in Cocoa Butter

Cocoa butter displays complex crystallization behavior and six crystal polymorphic forms. Although the crystal structure of cocoa butter has been studied extensively, the molecular interactions between cocoa butter triacylglycerols in relation to polymorphic transformations from metastable forms (forms III and IV) to stable crystal forms (forms V and VI) remain largely unknown. In this review, the triclinic polymorphism and melting profiles of the major triacylglycerols in cocoa butter-POP, POS, and SOS-are reviewed, and their binary and ternary phase behaviors in metastable (pseudoβ') and stable (β₂) crystal forms are discussed. We also attempt to clarify how the transformation of cocoa butter from form IV to V, as a critical step in the tempering of chocolate, is controlled by POS interactions with both POP and SOS. Moreover, we show how the crystal forms V and VI of cocoa butter are templated by crystal forms β₃ and β₁ of POS, respectively.

The presence of crystalline sugar limits the influence of emulsifiers on cocoa butter crystallization

The effects of 2 wt% emulsifier and crystalline sugar on the isothermal solidification and polymorphic behavior of cocoa butter were evaluated. The emulsifiers investigated were commercial soy lecithin, polyglycerol polyricinoleate (PGPR), citric acid esters of mono- and diacylglycerols (CITREM) and ammonium phosphatides (AP). All emulsifiers accelerated cocoa butter nucleation and growth from the melt, with PGPR showing the smallest enhancement. Lecithin and AP minimally affected the polymorphic form IV-to-V transition contrary to PGPR and CITREM, whichboth promoted the formation of form V crystals. The presence of sugar alone accelerated cocoa butter solidification while limiting the ability of the emulsifiers to do so. Sugar alone, and in the presence of emulsifier, hindered the polymorphic form IV-to-V transition. This study shows that the effects of emulsifiers on the isothermal crystallization of cocoa butter can be muted in the presence of crystalline sugar, suggesting a complex interplay dependent on emulsifier molecular structure.

Multiple β Forms of Saturated Monoacid Triacylglycerol Crystals

We have investigated the polymorphism of triacylglycerol (TAG) crystals as they affect the qualities such as shelf life, mouth feel, and texture of chocolate and other products. Saturated monoacid TAGs, like trilaurin, are considered as models for TAG crystallization; however, there is still debate about the number of their polymorphs that exist. In this study, we characterized a set of novel polymorphs, β forms of saturated monoacid TAGs, which were obtained via different pathways depending on the crystallization history, by polarized light microscopy, X-ray diffraction, and differential scanning calorimetry. Saturated monoacid TAGs were crystallized as the unstable polymorphs, the α or β’ forms first, and then they were transformed into β forms by solid–solid transformations. The β form that had transformed from β’ changed its morphology by a polymorphic transformation, while the β form made from the α form kept its spherulite morphology. The β forms obtained showed different melting points. Additional heat treatment promoted further polymorphic transformation. Four novel β forms were found for each of the saturated monoacid TAGs, trilaurin, trimyristin, tripalmitin, and tristearin. They showed similar polymorphism with the same subcell packing.

Early stages of fat crystallisation evaluated by low-field NMR and small-angle X-ray scattering

Low-field time-domain nuclear magnetic resonance (NMR; 20 MHz) is commonly used in the studies of fats in the form of solid fat content (SFC) measurements. However, it has the disadvantage of low sensitivity to small amounts of crystalline material (0.5%), thus often incorrectly determining crystallisation induction times. From spin-lattice relaxation rate measurements (R₁ ) during the isothermal crystallisation measurements of cocoa butter between 0.01 and 10 MHz using fast field cycling NMR, we learnt previously that the most sensitive frequency region is below 1 MHz. Thus, we focused on analysing our 10-kHz data in detail, by observing the time dependence of R₁ and comparing it with standard SFC_NMR and SFC determinations from small-angle X-ray scattering (SFC_SAXS ). Although not reflecting directly the SFC, the R₁ at this low frequency is very sensitive to changes in molecular aggregation and hence potentially serving as an alternative for determination of crystallisation induction times. Alongside R₁ , we also show that SFC_SAXS is more sensitive to early stages of crystallisation, that is, standard SFC_NMR determinations become more relevant when crystal growth starts to dominate the crystallisation process but fail to pick up earlier crystallisation steps. This paper thus demonstrates the potential of studying triacylglycerols at frequencies below 1 MHz for obtaining further understanding of the early crystallisation stages of fats and presents an alternative and complementary method to estimate SFC by SAXS.

Phase transitions in polymorphic materials probed using space-resolved diffusing wave spectroscopy

We use space-resolved dynamic light scattering in the highly multiple scattering regime (Photon Correlation Imaging Diffusing Wave Spectroscopy, PCI-DWS) to investigate temperature-induced phase transitions in polymorphic materials. We study paraffin wax as a simple model system and chocolate, a prototypical example of fat-based products exhibiting complex, history-dependent phase transitions. We find that microscopic dynamics measured using PCI-DWS show remarkable, non-monotonic behavior upon heating: they transiently accelerate when crossing phase transition and slow down above the transition temperature. Sub-micron resolution measurements of the local drift of the sample surface reveal that the speed-up of the dynamics is due to the strain field induced by the change in density at transition temperature. The transition temperatures obtained from PCI-DWS are found to be in excellent agreement with those inferred from complementary differential scanning calorimetry and X-ray scattering experiments, thereby validating PCI-DWS as a new, powerful tool for the characterization of phase transitions in complex soft matter. Finally, we demonstrate the unique possibilities afforded by space-resolved DWS by investigating the spatially heterogeneous response of poorly manufactured or composite chocolate samples.

Delaying fat bloom formation in dark chocolate by adding sorbitan monostearate or cocoa butter stearin

Two formulations of dark chocolate were developed by adding cocoa butter stearin (CBSt) or sorbitan monostearate (SMS) and compared to a standard formulation in order to investigate fat bloom formation over time. Fat bloom was monitored by Whiteness Index (WI), melting behavior and polymorphism determinations, in bars stored during 90 days at 20 °C and under oscillating temperature between 20 and 32 °C. All samples stored at 20 °C did not develop fat bloom and the required β(V) form was maintained. Under oscillating storage condition, samples with CBSt (6.0%, w/w) and SMS (0.15%, w/w) delayed the surface fat bloom formation by at least 45 and 15 days, respectively, compared to standard chocolate, observed visually and through WI increments. The β(V) to β(VI) polymorphic transition correlated well with the WI, and also with changes in DSC thermograms, confirming the higher effectiveness of specific triacylglycerol (mainly StOSt) in delaying bloom formation.

Isothermal Crystallization Behavior of Cocoa Butter at 17 and 20 °C with and without Limonene

Differential scanning calorimetry and real-time X-ray diffraction using synchrotron radiation were used to elucidate isothermal cocoa butter crystallization at 17 and 20 °C in the absence and presence of different limonene concentrations. At 17 °C, a three-step crystallization process was visible for pure cocoa butter, whereby first an unknown structure with long spacings between a 2L and 3L structure was formed that rapidly transformed into the more stable α structure, which in turn was converted into more stable β' crystals. At 20 °C, an α-mediated β' crystallization was observed. The addition of limonene resulted in a reduction of the amount of unstable crystals and an acceleration of polymorphic transitions. At 17 °C, the crystallization process was accelerated due to the acceleration of the formation of more stable polymorphic forms, whereas there were insufficient α crystals for an α-mediated β' nucleation at 20 °C, resulting in a slower crystallization process.

Tracking Structural Changes in Lipid-based Multicomponent Food Materials due to Oil Migration by Microfocus Small-Angle X-ray Scattering

One of the major problems in the confectionery industry is chocolate fat blooming, that is, the formation of white defects on the chocolate surface due to fat crystals. Nevertheless, the mechanism responsible for the formation of chocolate fat blooming is not fully understood yet. Chocolate blooming is often related to the migration of lipids to the surface followed by subsequent recrystallization. Here, the migration pathway of oil into a cocoa butter matrix with different dispersed particles was investigated by employing microfocus small-angle X-ray scattering and contact angle measurements. Our results showed that the chocolate powders get wet by the oil during the migration process and that the oil is migrating into the pores within seconds. Subsequently, cocoa butter is dissolved by the oil, and thus, its characteristic crystalline structure is lost. The chemical process provoked by the dissolution is also reflected by microscopical changes of the surface morphology of chocolate model samples after several hours from the addition of oil to the sample. Finally, the surface morphology was investigated before and after oil droplet exposure and compared to that of water exposure, whereby water seems to physically migrate through the particles, namely cocoa powder, sucrose, and milk powder, which dissolve in the presence of water.