Microstructure and mechanical properties related to particle size distribution and composition in dark chocolate

Composition in dark chocolate was varied and the effects determined on microstructure, using light microscopy, and mechanical properties of molten and tempered chocolates, using a TA.HD Plus Texture Analyser. Compositional parameters were particle size distribution (PSD) (D₉₀ of 18, 25, 35 and 50 μm), fat (25%, 30% and 35%) and lecithin (0.3% and 0.5%) contents. Micrographs revealed wide variations in sugar crystalline network structure and inter-particle interaction strengths related to PSD and fat level. Samples containing 25% fat had more crystal agglomerates, well flocculated with greater particle-to-particle interaction strengths than those with higher (30% and 35%) fat contents. Increasing the D₉₀ to 35–50 μm caused broadening of the PSD, with particles becoming coarser, which were similar at all fat levels. Mechanical analysis showed that PSD, fat and lecithin content significantly influenced firmness of molten chocolate and hardness of solid (tempered) chocolate with significant interactions among factors. Particle size was inversely correlated with firmness (1235–173 g) and hardness (7062–5546 g). Greatest effect of PSD was with 25% fat and 0.3% lecithin. With higher fat and lecithin contents, the PSD influence was reduced. It was concluded that PSD, fat and lecithin contents and their interactions were central to mechanical properties of dark chocolates.     

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.     

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.     

Comparison of rheological models for determining dark chocolate viscosity

Parameters in chocolate rheology, namely shear viscosity and yield stress, are important in manufacture and directly influenced by product particle size distribution (PSD) and composition. The Casson model was the standard confectionery industry strategy to quantify rheological properties of molten chocolate until in 2000, the International Confectionery Association recommended the use of interpolation data to describe viscosity. The two strategies are compared and correlated in defining rheological properties of molten dark chocolates prepared using different PSD, fat and lecithin content. Rheological parameters were determined using a shear rate-controlled rheometer and data examined using correlation, regression and principal component analyses to establish their inter-relationships. Correlation and regression analyses showed high correlation ( r  = 0.89–1.00) and regression coefficients ( R ² = 0.84–1.00). The newer International Confectionery Association technique gave higher correlation and regression coefficients than the Casson model, but multivariate principal component analysis showed that the two models were highly related and either could effectively quantify dark chocolate viscosity parameters.     

Functionality of inulin and polydextrose as sucrose replacers in sugar‐free dark chocolate manufacture – effect of fat content and bulk mixture concentration on rheological,mechanical and melting properties

Inulin and polydextrose are key bulk sugar replacers and have been utilised extensively as functional ingredients due to their fibre and prebiotic claims. This study investigated effects of fat content and bulk mixture concentrations of inulin and polydextrose on rheological properties, mechanical and melting characteristics of sugar‐free dark chocolates sweetened with steviol glycosides. Sucrose was replaced with polydextrose and inulin (0:100, 25:75, 50:50, 75:25, 100:0) at different fat contents (27%, 30% and 33%). Reducing fat content from 33% to 27% had similar effects on the sugar‐free dark chocolates as it did on reference chocolate. Increasing inulin concentrations with simultaneous reduction in polydextrose resulted in consistent increases in Casson plastic viscosity and decreases in Casson yield stress regardless of the fat content. These were explained by microstructural examination of the sugar replacers, which revealed wide variations in network structure. Understanding these factors would help reduce energy load from fat in sugar‐free chocolate confectionery.     

Rapid instrumental methods and chemometrics for the determination of pre‐crystallization in chocolate

Three rapid instrumental methods for the determination of the pre‐crystallization stage in six types of chocolate were studied. The methods were near‐infrared (NIR) spectroscopy, fluorescence spectroscopy and tri stimulus colour measurements. The chocolates were tempered into five categories: two levels of under‐tempered, two levels of over‐tempered and one level of well‐tempered chocolate. A temper meter was used as the reference method. NIR and fluorescence data were orthogonalized before modelling in order to remove the chocolate type characteristics. NIR spectroscopy was capable of discriminating between the five tempering groups when the principal component analysis (PCA) model was used on all chocolate types. A partial least squares discriminant analysis on the NIR spectra with the three main tempering groups (over‐, well‐, and under‐tempered) as the dependent variable showed perfect separation of the groups. Using fluorescence spectroscopy it was possible to separate the chocolates into the three main tempering groups in a PCA model, while the colour measurements did not reflect the degree of pre‐crystallization.     

Effects of particle size distribution and composition on rheological properties of dark chocolate

Control of chocolate viscosity is vital to its quality and production cost, and directly influenced by solids particle size distribution (PSD) and composition. Effects of PSD and composition on rheological properties of molten dark chocolate were investigated by varying PSD [D₉₀ (90% finer than this size) of 18, 25, 35 and 50 μm], fat 25, 30 and 35% and lecithin (0.3 and 0.5%) using a shear rate-controlled rheometer. PSD, fat and lecithin content significantly affected all rheological parameters, with significant interaction among factors. Increasing particles size gave significant reductions in Casson plastic viscosity, Casson yield value, yield stress, apparent viscosity and thixotropy, with greatest effect with 25% fat and 0.3% lecithin, which reduced with increasing fat and lecithin contents. Statistical analysis revealed that fat exerts the greatest effect on the variability in all the rheological properties followed by PSD and lecithin. PSD, fat and lecithin could be manipulated to control dark chocolate rheology, influencing quality whilst reducing production cost.     

Fat Bloom and Chocolate Structure Studied by Mercury Porosimetry

The structure of dark chocolate samples was analyzed by mercury porosimetry in order to determine whether the formation of fat bloom was related to the presence of pores. The influence of cocoa butter concentration and tempering conditions on porosity were determined by using samples containing 29.5 or 31.9% fat, which were under, well or over-tempered. All Mercury porosimetry analysis confirmed the presence of a porous structure in all chocolates. Empty spaces represented about 1% of the whole volume of a well-tempered chocolate containing 31.9% cocoa butter but made up about 4% of the over-tempered chocolate. A well-tempered chocolate with only 29.5% cocoa butter showed the presence of about 2% empty spaces. From these observations and gas permeability a possible model for the microscopic structure was developed.     

Influence of tempering and fat crystallization behaviours on microstructural and melting properties in dark chocolate systems

Particle size distribution (PSD) and temper influences on dark chocolate fat crystallization were studied using differential scanning calorimetry (DSC) and microscopy to establish relationships with their melting properties and microstructure. Variations in PSD had no influence on crystallinity of products at all temper regimes. Particle size (PS) increases had limited effects on T_onset, T_peak, and ΔH_melt independent of temper regime but significant decreases in T_end and T_index were noted. Contrary, varying temper regime influenced the crystallinity and melting properties (T_end, T_index and ΔH_melt) of products. Under-tempered chocolate showed widened crystal size distribution (CSD) with significant changes in T_end, T_index and ΔH_melt of products. Over-tempering caused moderate increases in CSD and melting properties, with significant effect on T_end, T_index and ΔH_melt but no changes were noted in T_onset, T_peak of products. Fat–sugar melting profiles showed similar levels in all products independent of temper regime, suggesting fat and sugar components are present in similar amounts in under-, over- and optimally-tempered products. Micrographs revealed clear crystalline network structure and well defined inter-crystal networks among tempered and over-tempered samples. Under-tempered products showed re-arrangement and re-crystallization of unstable fat crystals to smaller numbers of larger agglomerates with formation of solid bridges between the crystalline network structures. Attainment of optimal temper regime during pre-crystallization of dark chocolate is necessary for the achievement of premium quality products and avoidance of defects in structure and melting character.     

Use of Palm Mid-Fraction in White Chocolate Formulation

Samples of two types of palm mid-fraction (PMF I, a commercial sample and PMF II, from a laboratory-scale acetone fractionation of PMF I) and a Malaysian deodorised cocoa butter sample were used as the main components in the fat phase for white chocolate formulation. The monounsaturatedtriacylglycerol contents of these fats were 853, 899 and 903 g kg⁻¹, respectively.All the fats had free fatty acid contents of less than 10 g kg⁻¹ and melting points in the range of 34·0–34·5°C. The solid fat content profiles for the three fats were very steep. Differential scanning calorimeter analyses showed that all the fats had two melting peaks, T1 and T2. Results of the study showed that the tempering time to produce a well-tempered chocolate using PMF I was longer than that using PMF II, whereas, the time to produce a well-tempered cocoa butter chocolate increased with increase in the tempering temperature. Chocolates made with PMF I and II were well tempered between 17 and 19°C and with cocoa butter at 23°C. Thermal analyses, carried out on the chocolate showed that PMF I and II produced three melting peaks, T1, T2′ and T2 whereas most of the cocoa butter chocolates exhibited only one melting peak, T2. Storage studies showed that most of the chocolates had good bloom resistance for up to 12 weeks storage.     

Effect of ingestion of dark chocolates with similar lipid composition and different cocoa content on antioxidant and lipid status in healthy humans

The association between in vitro antioxidant capacity of dark chocolates with different cocoa percentage and the in vivo response on antioxidant status was investigated. In a randomized crossover design, 15 healthy volunteer consumed 100 g of high antioxidants dark chocolate (HADC) or dark chocolate (DC). In vitro, HADC displayed a higher Total Antioxidant Capacity (TAC) than DC. In vivo, plasma TAC significantly peaked 2 h after ingestion of both chocolates. TAC levels went back to zero 5 h after DC ingestion whilst levels remained significantly higher for HADC. HADC induced a significantly higher urinary TAC in the 5-12 h interval time than DC. No change was detected in urinary excretion of F2-isoprostanes. Plasma thiols and triacylglycerol (TG) levels significantly increased for both chocolate with a peak at 2 h remaining significantly higher for DC after 5 h respect to HADC. Results provide evidence of a direct association between antioxidant content of chocolate and the extent of in vivo response on plasma antioxidant capacity.     

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 2 h and tested for hardness. The effect of various EC viscosities (4, 10, 20, 22, and 45 cP) 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 26.0 N whereas the control chocolate was too soft to be tested. Further experiments revealed that white and dark chocolates had hardnesses of 29.5 and 10.5 N, 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.     

Structural characteristics of cocoa particles and their effect on the viscosity of reduced fat chocolate

Aimed at the manufacture of reduced fat chocolates, a novel method of trapped fat reduction was assessed: Manipulation of the cocoa ingredient. Cocoa mass was replaced with cocoa powder (11 g/100 g or <1 g/100 g fat) and added ‘free’ cocoa butter. A cocoa solids approach to design reduced fat chocolates with satisfactory flow properties is attractive to industry since it circumvents introduction of ingredients not commonly used in chocolate manufacture. Results showed that the cocoa mass chocolate had a higher viscosity than cocoa powder chocolates of the same total fat content due to the presence of trapped fat globules as identified by confocal laser scanning microscopy. The chocolate prepared with standard defatted cocoa powder containing 11 g/100 g fat had a lower viscosity than the chocolate containing highly defatted cocoa powder (<1 g/100 g) due to particle shape and fat diffusion into the particles as revealed by microscopy analyses. Based on the evidence presented, it can be concluded that standard defatted cocoa powder, as widely used by the industry, is indeed the best compromise in terms of free fat, particle size and morphology attempting to formulate fat reduced chocolate of acceptable molten state viscosity.     

Effect of storage temperature on texture,polymorphic structure,bloom formation and sensory attributes of filled dark chocolate

The effects of 18 and 30°C storage temperatures on texture, polymorphic structure, bloom formation and sensory attributes of dark chocolate, stored for 8 weeks were studied. Results showed that storage at 18°C for 8 weeks, significantly retarded changes in filled chocolates; the chocolates were free from bloom during the storage period. In contrast, at 30°C there was an increase in the rate of fat migration and rate of change of C36 and C50, and also a decrease in texture and the polymorph structure in the coating changed to β and β′ polymorphs. However, the chocolates bloomed in the third week of storage (2 cycles). Sensory evaluation indicated that, storage at 18°C is better than 30°C, and desiccated coconut gives a pleasant flavour to the chocolate.     

Thermal inactivation of Salmonella spp. during conching

Although chocolate is a microbiologically stable product it has been described as a vehicle for Salmonella spp. Because of the low water activity (a_w) and the high fat content of chocolate Salmonella spp. shows an increased heat resistance, even during the thermal process of chocolate making. The aim of this study was to evaluate the thermal inactivation of Salmonella spp. during conching in various masses of chocolate and cocoa butter at different temperatures (50-90 °C). The effect of thermal treatment on Salmonella spp. was determined with the MPN (Most-Probable-Number) method. Results of thermal treatment showed approximate D-values for cocoa butter from D_50°C = 245 min to D_60°C = 306 min, for cocoa liquor from D_50°C = 999 min to D_90°C = 26 min and for dark chocolate of D_50°C = 1574 min. z-values were found to be z = 20 °C in cocoa liquor and z = 14 °C in dark chocolate. This study demonstrates that the conching process alone does not ensure the inactivation of Salmonella spp. in different chocolate masses and that an additional decontamination step at the beginning of the process as well as an HACCP concept is necessary during chocolate production to guarantee the absence of Salmonella spp. in chocolates and related products.     

Enzymatically Modified Beef Tallow as a Substitute for Cocoa Butter

ABSTRACT: Dark "chocolate" samples were formulated with either cocoa butter (CB), randomized tallow (RT) made with Candida antarctica (SP 435) lipase, or a beef tallow: stearic acid structured lipid (SL) made by acidolysis using Rhizomucor miehei (IM 60) lipase. Fatty acid composition, thermal profile, solid fat content (SFC), hardness, and polymorphic structure were determined for the fats and/or "chocolate" samples. An accelerated fat bloom study was performed on the "chocolate" samples. Neither of the modified tallows had a detrimental effect on the crystallization of CB after proper tempering of the "chocolates." RT did not soften the "chocolate" and both of the modified lipids reduced bloom rates.     

Effects of selected properties of ultrafiltered spray-dried milk powders on some properties of chocolate

The effects of selected properties of spray-dried milk fat powders on chocolate were determined. Milk powders produced from control or ultrafiltered (UF) milks with various levels of fat were blended with skim milk powder to give a standard 26 g fat 100 g⁻¹ powder. Particle size of the chocolate mixes after refining decreased as the fat content and free-fat content of the powders increased. Despite this, increasing fat and free-fat contents of powders reduced the Casson viscosity of the subsequent molten chocolates. Casson viscosities using powders from control or UF milks were similar, but decreased as the particle size of powders increased and particle size after refining the chocolate mix decreased. Casson yield value and hardness decreased as fat content of powders increased. Casson yield value increased with vacuole volume of powders. It is possible to alter important properties of chocolates using milk powders of varying fat contents, free-fat contents and particle sizes.     

Effects of milk powders in milk chocolate

The physical characteristics of milk powders used in chocolate can have significant impact on the processing conditions needed to make that chocolate and the physical and organoleptic properties of the finished product. Four milk powders with different particle characteristics (size, shape, density) and "free" milk fat levels (easily extracted with organic solvent) were evaluated for their effect on the processing conditions and characteristics of chocolates in which they were used. Many aspects of chocolate manufacture and storage (tempering conditions, melt rheology, hardness, bloom stability) were dependent on the level of free milk fat in the milk powder. However, particle characteristics of the milk powder also influenced the physical and sensory properties of the final products.     

Thickening of molten white chocolates during storage

When white chocolates are kept molten in storage tanks, problems can arise due to uncontrolled thickening and solidifying of the chocolate mass. The thickening of molten white chocolate was simulated on a laboratory scale using a rotational rheometer under static conditions, interrupted by short shear periods to measure the increasing viscosity. Several chocolates having different dairy components and fat contents were investigated for their tendency to thicken. In addition, sorption isotherms for white chocolates were obtained using Dynamic Vapour Sorption at different temperatures. The sorption isotherms showed the presence of amorphous lactose in all the chocolates that were manufactured from milk powders. Moisture that is released during the crystallisation of amorphous lactose causes stickiness and agglomeration of the neighbouring particles and starts the thickening process. This process is highly temperature-dependent. On elevating the temperature the lactose crystallisation occurs at lower relative humidities. In order to reduce the tendency of white chocolate to thicken, a high free fat level should be maintained, based on a high total fat content and on the use of high free fat milk powders, preferably roller-dried whole milk powders or the combination of skimmed milk powder and anhydrous milk fat.     

Properties of sucrose-free chocolates enriched with viable lactic acid bacteria

Chocolate formulated with isomalt and enriched with lactic acid bacteria Streptococcus thermophilus MK-10 and Lactobacillus delbrueckii subsp. bulgaricus 151, added in the form of powdered yoghurt, prepared by spray-drying is a sucrose-free, low-calorie product with functional properties. The technique of the production of chocolate sweetened with isomalt and containing live cells of the aforementioned bacterial strains has been established. Physicochemical and sensory properties of this product as well as survival of cells during 6-months storage at 4 and 18 °C have been determined. The isomalt-containing yoghurt chocolates displayed satisfactory sensory attributes. Their calorific value and consistency (hardness) were similar to those of control sucrose-free chocolates. The total acidity of yoghurt and standard milk chocolates was also similar, whereas yoghurt-containing dark chocolates displayed higher acidity. The characteristics of yoghurt-containing chocolates were a relatively low solid substance content (96.82–96.91% w/w), low Casson viscosity and yield value for milk chocolate masses, and enhanced rheological parameters for dark chocolate masses compared with control sucrose-free chocolates. Because the total number of lactic acid bacteria after 6-months storage at 4 and 18 °C was high (approximately 10⁷ cfu/g), the sucrose-free yoghurt-containing chocolates can be regarded as functional foods.