Chocolate Surface Research Articles

Chemical Composition of Fat Bloom on Chocolate Products Determined by Combining NMR and HPLC-MS.

To reduce unwanted fat bloom in the manufacturing and storage of chocolates, detailed knowledge of the chemical composition and molecular mobility of the oils and fats contained is required. Although the formation of fat bloom on chocolate products has been studied for many decades with regard to its prevention and reduction, questions on the molecular level still remain to be answered. Chocolate products with nut-based fillings are especially prone to undesirable fat bloom. The chemical composition of fat bloom is thought to be dominated by the triacylglycerides of the chocolate matrix, which migrate to the chocolate's surface and recrystallize there. Migration of oils from the fillings into the chocolate as driving force for fat bloom formation is an additional factor in the discussion. In this work, the migration was studied and confirmed by MRI, while the chemical composition of the fat bloom was measured by NMR spectroscopy and HPLC-MS, revealing the most important triacylglycerides in the fat bloom. The combination of HPLC-MS with NMR spectroscopy at 800 MHz allows for detailed chemical structure determination. A rapid routine was developed combining the two modalities, which was then applied to investigate the aging, the impact of chocolate composition, and the influence of hazelnut fillings processing parameters, such as the degree of roasting and grinding of the nuts or the mixing time, on fat bloom formation.

Influence of PET as single-use contact material on gloss and surface properties of chocolate

Polyethylene terephthalate (PET) is a commonly used polymer in many industry sectors including confectionery industry. In the latter, PET is utilized for single-use moulds for chocolate manufacturing. Despite the broad application of PET in these areas, information regarding its influence on chocolate gloss and surface properties is not available. Meanwhile, it is already well established that fat crystal modification influence these properties (including gloss) distinctly. To bridge this disparity, this study examined how amorphous and glycol-copolymerized PET sheets influence non-pre-crystallised and pre-crystallised dark chocolate properties throughout a 28-day storage period. Polymorphic properties of cocoa butter were analysed via DSC. Non-pre-crystallised and pre-crystallised chocolate surfaces were characterised regarding colour, gloss, polarity, adhesion, roughness, and topography. While pre-crystallised chocolate shows consistent results, non-pre-crystallised chocolate experiences considerable changes in surface properties due to fat crystal transitions during storage. The findings show that the polymorphic state had a major impact on chocolate surface properties. Furthermore, results demonstrated that the type of PET had a significant impact on chocolate surface properties as well. Pre-crystallised chocolate gloss was significantly impacted by the choice of PET contact material. As a result, pre-crystallised chocolates exhibited a larger tendency to gloss inhomogeneities following amorphous PET monolayer sheet contact.

Influencing chocolate gloss inhomogeneities by the choice of surface-active substance and contact material

Gloss is an important criterion for chocolate quality and hence consumer acceptance. Gloss inhomogeneities, meaning glossy and matt spots on chocolate surfaces, remain a problem as they occur even after apparently optimal pre-crystallisation and cooling of chocolates. The presented study dealed with clarifying the complex interactions between dark chocolate with different surface-active substance (SAS) in contact with several mould materials by focusing on changes in chocolate surface properties and formation of gloss inhomogeneites. Contact materials used were polycarbonates (PC) and silicone. They varied in surface properties, specifically in roughness and surface free energy (SFE). PGPR, soy, and sunflower lecithin were used as SAS to alter the chocolate mass’ interface properties. Beside mould material’s surface properties, gloss (inhomogeneities), color, surface topography, roughness, and SFE were examined. Results showed that gloss and its inhomogeneities were significantly influenced by the contact material. Compared to PC, silicone had a significantly different impact on chocolate’s SFE and roughness. Topography images obtained by Atomic Force Microscopy revealed microstructural variations in the different gloss areas. Contact material and SAS had an impact on the microstructure as well. A statistical analysis further revealed that the contact materials' SFE and its dispersive share influence the formation of gloss inhomogeneites.

Spontaneous Pattern Growth on Chocolate Surface: Simulations and Experiments

The natural variation of temperature at ambient conditions produces spontaneous patterns on the surface of chocolate, which result from fat bloom. These metastable patterns are peculiar because of their shape and cannot be obtained by controlled temperature conditions. The formation of these spontaneous grains on the surface of chocolate is studied on experimental and theoretical grounds.Three different kinds of experiments were conducted: observation of formed patterns in time, atomic force microscopy of the initial events on the grain formation and rheology of the melted chocolate. The patterns observed in our experiments follow the trends described by the Avrami model, which considers a constant value at all spatial scales of the rate of linear growth α that governs the formation of isolated grains, starting from molecular clusters. Through NVT-ensemble computer simulations, using a Mie-segmented coarse-grained model of triacylglycerides molecules, we studied the process of nucleation that starts the pattern growth. From simulation and experiment results it is possible to derive a realistic value of α.

Fat Bloom Caused by Partial De‐Oiling on Chocolate Surfaces after High‐Temperature Exposure

AbstractFat bloom in chocolate is a substantial problem that affects its sensory properties, such as texture and appearance. This phenomenon is because of diffuse light reflection on a roughened surface of chocolate, caused by structural changes of fat crystals subjected to various temperature conditions. The purpose of this study is to characterize the fat bloom formed through gradual two‐step cooling after exposure to temperatures (35–37 °C) slightly above the cocoa butter Form βV melting point (33.8 °C). To clarify the fat bloom formation process, the structural changes in cocoa butter and on the chocolate surface, at the dynamic thermal condition for bloom formation, was investigated using X‐ray diffraction (XRD), fluorescence light microscopy, and scanning electron microscopy (SEM). The results revealed that an entirely light brown fat bloom occurred, even in the absence of the Form βVI or other polymorphic transformation. Microscopic observation showed that the light brown appearance was because of the porous structure on the chocolate surface. This porous structure was formed by liquid oil moving inside of chocolate from the surface. The formation of a coarse network and the subsequent de‐oiling, because of movement of unsolidified liquid fat into the chocolate, appeared to be the main causes of bloom formation. Therefore, a coarsened fat network and oil movement besides the conventional principles of polymorphic transformation of cocoa butter should be considered.

Portable NIR spectrometer for quick identification of fat bloom in chocolates

Cocoa butter provides desirable sensory properties to chocolates; however, the exposure of chocolate to temperature variations during transportation and/or storage can lead to changes in the polymorphic form of butter, with the appearance of a dull-white film on the chocolate surface, known as fat bloom. This study investigated the use of a portable NIR spectrometer combined with chemometric tools to discriminate milk chocolate, white chocolate, 40% cocoa chocolate, and 70% cocoa chocolate samples, which were subjected to temperature abuse for 6 hours. The PCA allowed separating the samples into three classes: control at 20 °C, chocolate subjected to 35 °C, and chocolate subjected to 40 °C, for each type of chocolate studied. The PLS-DA models provided sensibility, specificity, and accuracy values in the range of 80 to 100%, and allowed identifying the wavelengths associated with the different chocolates that most impacted the construction of the models.

Physical Chemical Properties of Shea/Cocoa Butter Blends and their Potential for Chocolate Manufacture

AbstractCocoa butter (CB) is the preferred fat for chocolates and confections. However, for technological and economic reasons, there have been strong efforts for partially replacing it. As shea butter (SB) has become an important natural source of symmetrical stearic‐rich triacylglycerols (TAG), the aim of this work was to study physical chemical behavior of blends of CB and SB and the dynamic mechanical and polymorphic behaviors of chocolates prepared with these systems as added fat. The compatibility of SB and CB blends was studied using the isosolid diagram. Data showed that softening occurred due to both dilution effects and a slight eutectic formation. Chocolates formulated with a fat phase consisting in CB, or SB, or blends with 10, 20, or 30 wt.% SB in CB showed different polymorphic behaviors during storage. The polymorphic transition from β2 to β1 occurred to a greater extent with increasing content of SB in formulation. Dynamic mechanical analysis (DMA) results agree with X‐ray findings. E′ modulus significantly increased during storage most likely due to formation of β1 form. As shown by Grazing incidence wide‐angle X‐ray scattering (GIWAXS) studies, crystals preferred growing on the chocolate surface than on bulk chocolate. However, even after a year at 18°C, chocolates had good appearance indicating that SB was a good CB extender.

Fat bloom formation on model chocolate stored under steady and cycling temperatures

In this study, two temperature cycling ranges, 20–29 °C and 20–32 °C, were used to promote bloom development on model chocolate, and control samples were stored at a constant 20 °C. Bloom formation was characterised based on visual inspection and surface colour analysis, while fat polymorphic transformation was monitored, and surface microstructure was examined. The control samples were highly bloom resistant and may exhibit solid-state polymorphic transformation. However, melt-mediated polymorphic transformation occurred under cycling temperatures; separated fat crystals formed on the chocolate surface under 20–29 °C cycling, while surface roughening occurred under 20–32 °C cycling, leading to differing bloom appearance. Additionally, the liquid fat content was higher when the temperature was cycled to 32 °C, than to 29 °C, and accordingly, bloom formation was also quicker. The pumping and capillary effects under the cycling temperatures led to fat migration to the chocolate surface, differing from the potential mechanism in the control samples.

Influence of supercritical fluid extract of Cinnamomum zeylanicum bark on physical, bioactive and sensory properties of innovative cinnamaldehyde-enriched chocolates

In the current investigation, the potential utility of cinnamaldehyde obtained from cinnamon (Cinnamomum zeylanicum) bark powder in enhancing the antioxidant capacity of dark chocolates was evaluated. To this end, the effects of conventional solvent extracts (CSE) and supercritical fluid extracts (SFE) on total phenolic contents, physical and sensory attributes of cinnamaldehyde-enriched chocolates were determined over the course of 60 days of storage. The addition of 0.5% nutraceutical<sub>SFE</sub> and 1% nutraceutical<sub>CSE</sub> extracts significantly increased the total phenolic contents of the chocolates to 15.62 ± 0.35 mg GAE/g and 13.31 ± 0.26 mg GAE/g in T<sub>2</sub> and T<sub>1</sub>, respectively. In terms of texture (hardness), 0.5% extract resulted in softer chocolates (64.87 ± 2.41 N) as compared to the control (70.91 ± 2.83 N). At storage termination, colorimetric results revealed a whitening of the chocolate surface that resulted in incremental increases in L* and b*, whereas a* exhibited a declining trend. Moreover, the sensory results showed a better hedonic response for the enriched products. Taken together, cinnamaldehyde enrichment is beneficial for both the functional as well as oxidative stability of chocolates. Chocolate, as the most commonly craved food product, is gaining much attention from the manufactures as a potential vehicle for the delivery of functional health benefits. In this study, we used cinnamaldehyde and maltitol (sugar replacer) to prepare functional chocolates with a special emphasis on diabetic patients, an approach that will open new horizons for innovative product development. We also optimised and characterised the extraction conditions for bioactive components using green extraction technology, i.e. a supercritical fluid extraction technique which is cost-effective and environmentally friendly.

Oil migration in hazelnut paste/chocolate systems using magnetic resonance imaging

Oil migration in confectionery products results in undesired quality changes of confections such as fat bloom. Oil migration and the resulting bloom formation in chocolate could be an important quality defect in a confectionery product. This study addressed to evaluate mass transfer of liquid oil on two-layer chocolate model systems prepared from hazelnut paste over different dark chocolate formulations by utilizing magnetic resonance imaging (MRI). Through the use of MRI, it becomes easier to predict the rate of migration and the effect of different ingredients on bloom formation. For five chocolate formulations stored at 30 °C over a time frame of 22 days, experimental data acquired through MRI were modeled using a Fickian-based mathematical model to calculate diffusion coefficient (D). Using two different equations for boundary condition at upper chocolate surface, two models were evaluated and logistic type boundary model was shown to fit exhibit a better fit. In addition, associated constants (C0, β, t0) for time dependent upper boundary conditions were determined. Average diffusivities of all samples varied in the order of 10−11 m2/s. This study addressed the potential use of MRI for visualization and quantification of migration for different chocolate formulations.

Peculiarities of diffraction gratings application on chocolate surface

Peculiarities of diffraction gratings application on chocolate surface

Changes in contact angle providing evidence for surface alteration in multi-component solid foods

Chocolate blooming, one of the major problems in the confectionery industry, is the formation of visible white spots or a greyish haze on the surface of chocolate products due to large sugar or fat crystals on the surface. This leads to aesthetic changes and deterioration of taste and thus large sales losses for the confectionery industry due to consumer complaints. Chocolate blooming is often related to migration of lipids or sugar molecules to the chocolate surface, where they recrystallize with an associated polymorphic change of crystal structure on the surface. The wetting behaviour from contact angle measurements gives further insight into surface properties and is needed to determine surface energies and to evaluate possible migration mechanisms and preferred pathways. Therefore, an equilibrium contact angle is needed which is not directly accessible and is influenced by surface texture and interaction between solid and test liquid. In this study, the surface of cocoa butter and conventional chocolates was characterized by measuring the contact angle with the sessile drop protocol. The influence of roughness, test liquid and pre-crystallization of the samples as well as the storage temperature were investigated. In case of no pre-crystallization, a change in surface properties due to storage at 20 °C was detected, whereas samples stored at 30 °C showed the same wetting behaviour as fresh samples. This is associated with polymorphic transformation from thermodynamically less stable crystals to more stable configurations.

Controlling the stability of chocolates through the incorporation of soft and hard StOSt‐rich fats

The presented study investigates the functionality of hard and soft StOSt‐rich fats in plain and hazelnut‐based filled dark chocolates. Blends of cocoa butter (CB) with different StOSt‐rich fats, namely Vietnamese mango fat (VMF), Indian mango fat (IMF), its stearin (IMFst) and olein fraction (IMFol) were selected for application in these chocolate products based on their phase and crystallisation behaviour. It was shown that a fat phase formulation with CB/VMF 70/30 and CB/IMFst 70/30 increased the heat resistance of dark chocolate and maintained similar chocolate quality attributes (colour, hardness, melting and flow properties) compared to the CB reference. Furthermore, these fat blends increased the fat bloom stability following oil migration, as shown by visual assessment by a trained panel, cryo‐SEM imaging and oil migration monitoring by HPLC‐ELSD. In addition, the fat blend CB/IMFol 90/10, suitable for chocolate applications under non‐tropical conditions, was shown to retard oil migration fat bloom as well. Distinct mechanisms for the observed phenomena were proposed. Furthermore, the different steps of fat bloom development, starting from the appearance of oil blisters to the presence of crystals (∼30 μm) on the chocolate surface were captured using cryo‐SEM.Practical applications: (i) heat resistant chocolate with increased fat bloom stability was developed; (ii) fat boom development in filled chocolates can be delayed tuning the TAG composition and (iii) a cost‐effective source of mango fat was provided with several technical applications for the tropics.By tuning the TAG composition, several compatible fat blends of cocoa butter (CB) and mango fats (MF) are obtained. In comparison to the CB reference chocolate, the fat phase formulation with hard StOSt‐rich fats (CB/VMF 70/30 and CB/IMFst 70/30) increases the heat resistance of dark chocolate likely without inducing a waxy mouthfeel. Furthermore, both hard and soft StOSt‐rich fats increase the stability towards oil migration fat bloom, as observed by cryo‐SEM imaging. Explanations are proposed based on TAG composition.

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.

Oil migration: Novel approaches to a familiar problem

Oil migration in chocolate and chocolate‐coated confections is a familiar yet poorly understood phenomenon that results in undesirable product changes including softening of chocolate coatings and fat bloom on the chocolate surface. Understanding the mechanism behind oil migration would benefit manufacturers as it would aid in maximizing product shelf life and reducing consumer rejection, but current models prove too simplistic to account for the complex nature of chocolate. This review briefly summarizes recent works attempting to move beyond a simple diffusion‐based model by employing new modeling or experimental techniques.

Influence of cocoa butter diacylglycerols on migration induced fat bloom in filled chocolates

As migration induced fat bloom remains one of the major quality issues in composite chocolate products, this study investigated whether cocoa butter based DAGs could delay or prevent this phenomenon. A model system consisting of a plastic cylinder with filling and chocolate was utilized for this purpose. Using an automated image analysis procedure, the surface of the chocolate was examined at regular time intervals to detect the presence of fat bloom crystals. The chocolate was cut into different layers and analyzed by HPLC and DSC to monitor the oil migration. It was noticed that the quality characteristics of the plain chocolates only slightly changed during the 1‐year storage period. DSC thermograms demonstrated that the oil migration was a triggering factor for the re‐crystallization to βVI crystals, protruding through the chocolate surface resulting in a grayer and duller appearance. The model based on Fickian diffusion with a constant diffusivity failed to accurately describe the migration of oil into chocolate. Non‐Fickian behavior occurs as besides migration, interaction between oil and cocoa butter can also play a major role. It was concluded that the presence of DAGs did not delay oil migration, nor prevented the appearance of migration induced fat bloom.The performance of the DAG chocolates containing up to 7.5% DAG on fat base, on the occurrence of fat bloom was evaluated. A model system consisting of a plastic cylinder with filling and chocolate was utilized for this purpose, plain chocolates were used as reference. The figure shows peak area of the main melting peak as determined by DSC, of the top layer as function of storage time for the plain chocolate (a) and chocolates with filling (b) (legend represents the % DAG on fat base). It could be concluded that oil migration from the filling was a triggering factor for the re‐crystallization to βVI crystals, protruding through the chocolate surface resulting in a grayer and duller appearance.

Ethylcellulose solvent substitution method of preparing heat resistant chocolate

In the present study a structuring technique was developed to produce chocolate which resists deformation at temperatures above 40°C. It was hypothesized that by adding ethylcellulose (EC) solubilized in ethanol (EtOH) to chocolate and evaporating the EtOH an organogel could be formed in situ with the fat phase of the chocolate. Heat resistant chocolate (HRC) was produced by mixing a 20% EC in EtOH solution with molten chocolate. The EtOH was evaporated and the resulting chocolate was incubated at 40°C for 2h and tested for hardness. The effect of various EC viscosities (4, 10, 20, 22, and 45cP) and concentrations ranging from 1.0 to 2.2% on different types of chocolates was studied. Milk chocolate containing 1.9% EC had a hardness of 26.0N whereas the control chocolate was too soft to be tested. Further experiments revealed that white and dark chocolates had hardnesses of 29.5 and 10.5N, respectively. The hardness of the chocolate was dependent on the chocolate formulation and concentration of EC, and independent of EC viscosity. It was observed that the addition and evaporation of EtOH from the compound milk chocolate samples led to an increase in the lightness of the chocolate surface if the EtOH was evaporated at temperatures of 40°C or higher. Addition of EC to chocolate represents a new strategy for the manufacture of HRC. Future work should focus on determining the mechanism by which heat resistance is achieved in these chocolates.

Study of the porous structure of white chocolate by confocal Raman microscopy

AbstractConfocal Raman microscopy has been shown to be a useful technique for investigation of white chocolate surfaces. The appearance of protrusions and pores, and the distribution of fat, sucrose, and milk powder at and below the surface of white chocolate pralines were investigated using confocal Raman microscopy. Raman horizontal and depth scans showed that the protrusions and pores continue at least 10 µm into the chocolate shell and that some protrusions and channels mainly consist of fat, while some consisted of a fat layer, leaving a hollow space underneath. Further, the pores and their continuing channels consisted of nothing but air. These findings indicate that the protrusions might be connected to channels where we suggest a pressure driven convective flow of liquid fat from within the chocolate matrix that, depending on temperature, moves up to the surface or goes back into the matrix, leaving an empty pore with a shell of fat at the surface, which in some cases collapse and leaves a hollow pore and channel. Therefore, these findings support that the protrusions could be connected to oil migration in chocolate and, thus, further to fat bloom development.Practical applications: Confocal Raman microscopy can be used to investigate the local distribution of different components in white chocolate. This technique offers the possibility to acquire the local distribution of different components within the sample, with a resolution down to the optical diffraction limit. Further, the analysis can be performed at ambient conditions, without requiring any special sample preparation or marker molecules. The results obtained by using this technique suggest that specific surface imperfections on chocolate could be part of a network of pore structures at and beneath the chocolate surface, which could be related to oil migration and thus, to fat bloom formation.

Raman spectroscopy of the polymorphic forms and liquid state of cocoa butter

AbstractRaman spectroscopy was used to characterize the polymorphs and liquid state of cocoa butter, with emphasis placed on the evolution of the ester carbonyl stretching region (1800–1700 cm−1), along with complementary analysis and comparison of the Raman‐active CC (1200–1000 cm−1), CC (1660 cm−1), CH (3000–2700 cm−1) and CH2 (1500–1250 cm−1) vibrational modes. Unique Raman signatures were obtained for all cocoa butter polymorphs, with their identity confirmed using DSC and XRD. The ester carbonyl region permitted polymorph discrimination due to differences in the number of modes, their relative frequencies and their full‐widths at half‐maximum. The CC stretching modes, which provided insight into the trans/gauche content, were polymorph‐independent. CH stretching generally increased with polymorph stability, indicating the dominance of antisymmetric CH methylene vibrations as the cocoa butter crystal lattice became more ordered. The change in the intensities of the CH stretching bands used to probe the order–disorder transition of forms IV, V and VI hinted at pre‐melt structural changes mostly in forms IV and V. Overall, Raman spectroscopy clearly demonstrated that the different functional groups studied could be characterized independently, allowing for the understanding of their role in cocoa butter polymorphism.Practical applications: Fat bloom is the unwanted, uncontrolled re‐crystallization or polymorphic transition of CB form V crystals into form VI normally caused by the migration of lower‐melting fats (e.g. in centre‐filled products) and/or temperature fluctuations during storage. In its mildest form, it appears as an overall dulling of the chocolate surface. In its extreme form, the appearance of the chocolate deteriorates significantly with the development of distinct white patches. Though forms V and VI can be clearly distinguished via XRD, we present evidence that Raman spectral characterization of the ester carbonyl stretching (1800–1700 cm−1), CC (1200–1000 cm−1), CC (1660 cm−1), CH (3000–2700 cm−1) and CH2 (1500–1250 cm−1) vibrational modes yields distinct liquid–solid and polymorph‐dependent differences in CB. From a practical standpoint, the unique signatures associated with forms V and VI offer novel possibilities in the study of fat bloom formation, such as the development of predictive tools.

Investigation of Chocolate Surfaces Using Profilometry and Low Vacuum Scanning Electron Microscopy

AbstractIn this study we establish the use of optical non‐contact profilometry combined with low vacuum scanning electron microscopy (LV SEM) for the investigation of lipid surfaces. We illustrate, by using profilometry, a methodology for investigation of chocolate surface topology as a function of time, in the same area of interest. Both qualitative and quantitative data analysis has been performed for profilometry data. Further, relating these results to LV SEM images provides complementary topological information and hence a useful toolkit for the study of the chocolate surface prior and post fat bloom formation. For the demonstration of the successful combination of these two analytical techniques, white chocolate pralines were stored at two temperature‐controlled conditions (at 18 °C, and cycled between 15 and 25 °C). Surface properties were then investigated during 36 weeks of storage. The surface images and the roughness parameters indicated distinct development of surface characteristics for the two storage conditions. From the results it is suggested that some imperfections, in the form of pores or protrusions, could play a role in fat bloom development and that there may be different main mechanisms of fat migration taking place for the different storage environments. In the present work, a positive correlation of profilometry data to chocolate surface characteristics and early bloom development has been established. There are indications that early prediction of fat bloom can be possible, however further work needs to be done to quantify prediction of fat bloom.