Impact of pre-crystallization process on structure and product properties in dark chocolate

Dark chocolate microstructures with different structure densities, i.e., close-packing of the fat crystal lattice, and homogeneity i.e., evenness and connectivity of the fat crystal network, were created by β_VI-seeding or conventional pre-crystallization with various degrees of temper and were evaluated with respect to storage stability. The structure characterization was conducted by measuring the strength of the cocoa butter crystal network with traction tests combined with DSC melting curves. Subsequent storage stability was evaluated with DigiEye technique for fat bloom development and gravimetrical techniques for fat/moisture migration. The two pre-crystallization processes generated significantly different structures and storage stability. Well-tempered β_VI-seeding resulted in a dense and homogenous chocolate structure directly after solidification, which was optimal in order to retard fat bloom and fat migration. However, a too high structure density generated heterogeneous structures with reduced ability to withstand fat bloom. A lower structure density exhibited optimal resistance against moisture migration.     

Oil migration in chocolate and almond product confectionery systems

Oil migration from high oil content almond confections into adjacent chocolate causes changes in product quality. The objective of this study was to quantify the oil migration from almond products to dark chocolate. Magnetic resonance imaging (MRI) was used to monitor spatial and temporal changes of liquid lipid content. A multislice spin echo pulse (MSSE) sequence was used to acquire images with a 7.8-ms echo time and a 1000-ms repetition time using a 1.03T Aspect AI MRI spectrometer. Samples were prepared as a 2-layer model system of chocolate and almond confection. Six different almond products and 1 type of dark chocolate were used. Samples were stored at 20, 25, and 30°C for a time frame of several months. Rate and extent of migration were quantified by a kinetic expression based on the linear dependence of oil uptake by chocolate and the square root of the time. Samples showed distinctly different rate and extent of oil migration, as evidenced by quantitative differences in the kinetic rate constants and equilibrium uptake for the different sample types. This work will be helpful to design formulations for almond and almond-based products in confections. PRACTICAL APPLICATION: This work will be helpful to design formulations for almond use in confections.     

Visualisation of Liquid Triacylglycerol Migration in Chocolate by Magnetic Resonance Imaging

This study has demonstrated that magnetic resonance imaging can be used to visualise the migration of liquid triacylglycerols in composite chocolate confectionery. Migration was observed between a layer of hazelnut oil filling (oil+icing sugar) and a layer of dark chocolate used as a model of composite chocolate confectionery products. In addition, low-resolution nuclear magnetic resonance measurements of the solid fat content (%) were also made. Substantial differences were observed between the migration profiles at 19 and 28°C, and in the distribution of liquid triacylglycerols across the chocolate layer after migration. It is suggested that the mechanism of migration involves both diffusion of the liquid triacylglycerols and capillary attraction of the hazelnut oil into the chocolate matrix. © 1997 SCI.     

Oil Migration in a Chocolate Confectionery System Evaluated by Magnetic Resonance Imaging

ABSTRACT: Oil migration is a common problem in composite chocolate confectionery products resulting in softening of chocolate and hardening of the filling. Spatial and temporal changes in the liquid oil content of a 2-layer peanut butter and chocolate model system were evaluated using a magnetic resonance imaging (MRI) technique. The experimental factors were chocolate particle size, milk fat content, emulsifier concentration, degree of temper, and storage temperature. The responses were migration rate and overall change in signal intensity (amount of migration). Based on analysis of variance (ANOVA), particle size, milk fat content, and storage temperature were significant factors for oil migration rates. Milk fat content and temperature were significant factors for overall change in signal intensity.     

Technofunctional barrier layers for preventing fat bloom in triple-shot pralines

The storage stability of dark chocolate with nougat fillings is mainly limited by the formation of fat bloom, which arises because of the migration of nut oil from the filling to the outside of the chocolate shell where it leads to the formation of visible cocoa butter crystals. The triple-shot technique, which allows the simultaneous deposition of three viscous fluids, was applied for the laboratory-scale manufacture of pralines with a technofunctional barrier layer to prevent blooming. Base component of the barrier layer was palm kernel oil, pure or in combination with milk fat; micro-milled sugar or skim milk powder served as disperse phase. As compared to control experiments, the formation of fat bloom was significantly reduced for selected barrier layers because of the reduced transfer of nut oil to the outside of the praline shells. These results indicate that triple-shot depositing is a promising technique for the manufacture of filled chocolate with enhanced physical shelf life.     

Application of kokum (Garcinia indica) fat as cocoa butter improver in chocolate

Although cocoa butter (CB) is an ideal fat for use in chocolate, it softens with heat and is not suitable for use in warm climates. CB extenders or improvers, preferably from stearic acid‐rich fats, are good candidates to increase the heat‐resistance property of CB and chocolate. In the present investigation, one such fat, kokum, is used as an improver to increase the hardness of chocolate. Kokum fat is added in various proportions replacing CB in dark and milk chocolate formulations and its effects on rheology, hardness and triglyceride composition were studied. The results revealed that up to 5% kokum fat addition by weight of the product did not significantly affect the plastic viscosity or yield stress of milk or dark chocolate. Hardness of both dark and milk chocolate increased with increase in addition of kokum fat. The solids fat content at and above 30 °C increased with increase in level of kokum fat with CB, especially at and above 15%. These physical properties are due to increase in 2‐oleodistearin triglycerides with addition of kokum fat with CB. The results revealed that kokum fat could be used up to 5% by wt of the product to increase the heat‐resistance property of chocolate so that it can be used in warm climates. Copyright © 2004 Society of Chemical Industry     

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.     

Effect of nut oil migration on polymorphic transformation in a model system

Fat migration in confectionery products can lead to significant deterioration in quality. This occurs not only through loss in texture contrast between chocolate and filling but also through the appearance of fat bloom on the surface of the chocolate. This latter aspect is often, although not exclusively, linked to the transformation of the cocoa butter β_V phase into β_VI. In this study, the influence of hazelnut oil on the polymorphic transformation of cocoa butter has been determined, showing that even small additions (1%) of nut oil can have a significant impact on the rate of transformation. Additionally, use of a model system has shown that polymorphic transformation in cocoa butter is linked to the degree of migration of nut oil from a filling. Portions of the cocoa butter close to the filling experience both greater degrees of migration and faster transformation.     

Lipid migration in two-phase chocolate systems investigated by NMR and DSC

The migration of lipids in two-phase chocolate systems (i.e. lauric acid+chocolate and peanut butter+chocolate) was analyzed by magnetic resonance and differential scanning calorimetry. Kinetics of fat migration was evaluated and the diffusion coefficient of lauric acid in chocolate was found to be dependent on migration time. This may be due to the capillary nature of fat migration in chocolate. Fat bloom characteristics were determined and related to the thermal history of samples and the presence of fat in the chocolate layer. Both lauric acid and peanut butter increased the liquid-to-solid ratio of chocolate and helped prevent fat bloom.     

The production of clusters in milk chocolate

Cluster production during conching of milk chocolate leads to defects in chocolate quality. Various conditions of conching, using two types of milk chocolate were examined. Temperature and relative humidity were the parameters that were controlled. The contents of moisture, fat, sucrose and lactose and also cluster development in milk chocolate during conching were evaluated. Representative samples in the conching tests were subjected to particle size analysis (using laser diffraction and sieve methods), X-ray diffraction analysis, polarizing microscopy and sensory evaluation.     

Fat Migration in Chocolate: Diffusion or Capillary Flow in a Particulate Solid?—A Hypothesis Paper

ABSTRACT: The exact mechanism of fat and oil migration in chocolate and chocolate coatings is still unknown. Nevertheless, the so-called "diffusion equation" derived from Fick's 2nd law has been extensively used to model the phenomenon, giving the impression that molecular diffusion is the single transport mechanism. We propose that chocolate may be microstructurally regarded as a particulate medium formed by an assembly of fat-coated particles (for example, cocoa solids, sugars crystals, and milk powder). Within this matrix the liquid fraction of cocoa fat (which increases with temperature) is likely to move under capillary forces through interparticle passages and connected pores. Based on available evidence (microstructure, kinetic data, temperature dependence of liquid fat fraction, and so on) we demonstrate that capillary forces may have an important role to play in bulk flow of liquid fat and oils. The Lucas-Washburn equation for capillary rise fits available data under most reported experimental conditions. Detailed microstructural analysis in actual products as well as data on key parameters (surface tension, contact angle, viscosity) is necessary to confirm this hypothesis. Bulk flow due to capillary effects, highly disregarded in structured foods, should be considered as a mass transfer mechanism in liquid-filled porous or particulate foods.     

Moisture and sucrose transfer in fractionated palm kernel (PKO) based films immersed in liquid solutions

The effects of addition of sucrose, lecithin, and cellulose on unsteady state diffusivity and steady state permeability of moisture through fractionated palm kernel oil (PKO)-based films were studied under liquid-induced moisture migration at a water activity gradient of 1.0 and at a temperature of 25 °C. Addition of sucrose, cellulose, and lecithin into the fat films decreased the diffusivity of moisture, but increased the permeability of moisture due to the high moisture sorption capacity of these hydrophilic components.The effect of sucrose concentration and the presence of sugar ester in the aqueous phase on the diffusivity and permeability of moisture through the fat-based film were also studied. For pure PKO films, sucrose concentration of the aqueous phase and presence of sugar ester in the aqueous phase had no effect on the diffusivity and permeability. For fat-based films containing sucrose, with increasing sucrose concentration of the aqueous phase, the diffusivity increased but the permeability decreased. Presence of sugar ester at 0.3% in the aqueous phase significantly increased permeability of the fat-based films containing sucrose.The mass transfer coefficient for sucrose leaching from the fat based films into the aqueous phase increased with sucrose content in the film. The rate of sucrose leaching out from the fat film into 0.3% sugar ester solution was higher than that into pure water. The diffusivity of sucrose in the fat film leaching out into the aqueous phase increased with sucrose content in the fat films.     

Automated image analysis tool for migration fat bloom evaluation of chocolate coated food products

Migration fat bloom remains a major problem in the production of coated confectionary products where a layer of chocolate is added around a filling or other fat containing substrate. Fat bloom quantification is typically done by a human panel scoring samples in time using a low resolution discrete scale. In view of developing a mechanistic model for migration fat bloom, it is important to have a higher resolution. In this paper, a new, high resolution quantitative method based on image analysis is developed. The method is able to detect both the evolution of fat bloom in terms of the disappearance of gloss and the development of “whitish” portions at the chocolate surface. It was successfully applied to distinguish the difference in fat bloom development rate between samples containing different fat concentrations (0, 3 and 6g/100g) coated on fillings containing different amounts of fat (25 and 75g/100g). In the 25g/100g filling fat case, blooming occurred at a very late stage and was caused by the disappearance of gloss. In the 75g/100g filling fat case the development of a “whitish” surface was responsible for the change in acceptability. The newly developed image analysis method is a solid alternative for the panel procedure.     

TEXTURAL CHANGES IN CHOCOLATE CHARACTERIZED BY INSTRUMENTAL AND SENSORY TECHNIQUES

Cocoa butter has a distinct texture due to unique interactions of polymorphic lipid structures. Part of chocolate's appeal is smooth mouthfeel; as fat or sugar bloom forms, textural change is perceived. Correlation of instrumental and sensory texture analysis has not been conducted in stored chocolate. The objective of this study was to analyze texture and color of dark and milk chocolate stored under conditions leading to fat and/or sugar bloom by instrumental and sensory measurements. Milk and dark chocolate was stored 5 weeks at various temperatures and relative humidity (RH), followed by instrumental and sensory texture analysis. All attributes, except springiness, were significantly affected by treatments. According to partial least squares linear regression, instrumental hardness, cohesiveness, chewiness and gumminess modeled sensory hardness. The 30.0C incubator experienced temperature fluctuations, resulting in severe fat bloom. Temperature fluctuations during storage had more influence on texture perception than storage at high temperatures or high RH.

PRACTICAL APPLICATIONS

This research serves as an initial study on textural aspects of chocolate quality upon storage that is the first report to correlate instrumental textural analysis of chocolate to sensory evaluation. Storage temperature and humidity of chocolate greatly impacts consumer texture perception, which is valuable information to small chocolate handlers and manufacturers who have noted to us that many of the larger companies may have this information – but it is not widely available. It also sets the stage for more detailed studies on texture and flavor of chocolate during storage. Although many storage studies on chocolate exist, those that intertwine studies of quality from both an instrumental and a sensory standpoint are lacking.     

Monitoring Tempered Dark Chocolate Using Ultrasonic Spectrometry

Ultrasonic spectrometry was used to distinguish between properly tempered and untempered commercial dark chocolate. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to characterize the polymorphic state of tempered and untempered chocolate, results that were correlated to those of ultrasonic spectrometry. Four different kinds of dark chocolate samples with different amounts of sugar (7.5–50 %), fat (30–50 %), and cocoa mass (70–90 %) were subjected to two different tempering protocols. The tempering was achieved using cocoa butter seeds under static cooling from 50 to 14 °C. The ultrasonic generator and analyzer SIA-7 (V.N. Instruments) was used to monitor the crystallization process. The instrument generated a chirp signal with a bandwidth of 0.5 to 3 MHz and was set to work in a four-pathway configuration with two transducers and a center frequency of 2.25 MHz. Spectrometric analysis was carried out with chocolate samples containing 2, 4, and 6 % solid fat content (SFC). The SFC was obtained from DSC measurements. Ultrasonic signals for attenuation, reflection, and velocity were compared between tempered and untempered chocolates. It was shown that seed-tempered chocolate with 30 % sugar and 47.5 % fat attenuated 2.5 MHz of ultrasonic waves by 0.8, 1.7, and 2.0 dB/cm at 2, 4, and 6 % SFC, respectively. On the other hand, untempered chocolate attenuated the ultrasound signal by 3.5, 3.6, and 4.3 dB/cm. Furthermore, it was found that ultrasound reflection signals were stronger and ultrasonic velocity was higher in chocolates with high sugar content.     

Effect of cocoa butter structure on oil migration

Oil migration from a high oil content filling into adjacent chocolate causes changes in product quality. The objective of this study was to quantify the oil migration from a cream filling system into cocoa butter, which provided a model for the behavior of chocolate-enrobed confectionery products with a soft, creamy center. Magnetic resonance imaging (MRI) was used to monitor spatial and temporal changes of liquid lipid content. A multislice spin echo pulse sequence was used to acquire images with a 7.8 ms echo time and a 200 ms repetition time using a 1.03 T Aspect Imaging MRI spectrometer. Samples were prepared as a 2-layer model system of cocoa butter and model cream filling. Three methods were used to prepare the cocoa butter: static, seeded, and sheared. Samples were stored at 25 °C for a time frame of 56 d. The rate of oil migration was quantified by a kinetic expression based on the linear dependence of oil uptake by cocoa butter and the square root of the time. Samples showed distinctly different rates of oil migration, as evidenced by quantitative differences in the kinetic rate constant. Practical Application: This work will be helpful to elucidate the influence of crystallization process and structural properties such as crystal nanostructure and crystal habit on the migration of oil through a crystalline fat matrix.     

The application of Borneo tallow in dark chocolate shell

Dark chocolate shells, formulated using cocoa butter (CB shell), and fat blends containing 15% Borneo tallow (IP) in cocoa butter (CBIP shell), were filled with truffles formulated using white chocolate (W truffle), milk chocolate (M truffle) and dark chocolate (D truffle). Anhydrous milk fat (AMF) content of the W truffles, M truffle and D truffle were 26·3%, 13·7% and 9·2%, respectively. Degree of tempering was determined using a tempermeter. The chocolates were kept at ambient temperature (25·5±0·5°C) for 3 months. Physical changes of chocolate shells and centres were monitored using DSC and a texture analyser. Results showed that the CBIP shell had to be tempered at 32·5%, ie 1°C higher than the normal CB shell. Physical measurements indicated the occurrence of fat migration. The presence of IP reduced the effect and increased the bloom resistance of the chocolate. © 1998 SCI.     

The role of nonfat ingredients on confectionery fat crystallization

Confections such as chocolate and biscuit fillings are composed of a continuous fat phase that contains dispersed nonfat ingredients such as sugar and cocoa powder. Research on fat crystallization and rheology in confections often extrapolates crystallization and textural properties from bulk to mixed systems while overlooking the important role of composition or particle interactions. For example, in chocolate processing the fat phase aids dispersed phase lubrication and fluidity whereas the dispersed particles assist in fat crystallization by providing many nucleation sites. In confections with a high dispersed phase volume fraction, fat crystallization may be hindered due to reduced triacyglycerol mobility, confinement, and increased tortuosity. This is further complicated in systems with slow crystallizing fats such as palm oil whose crystallization is exceptionally sensitive to composition and processing. This review breaks down the physical chemistry of fat-based confections and discusses the impact of different nonfat ingredients towards fat crystallization and rheology. The behavior of palm oil is further highlighted as it is becoming increasingly popular as a confectionery ingredient. Lastly, ingredient-ingredient interactions and their role in fat crystallization are described along with force spectroscopy as a novel tool to characterize such phenomena. Force spectroscopy utilizes atomic force microscopy to measure intermolecular forces as a function of distance but remains largely unexplored in the area of food science.