Ataxin-3 (AT3), the disease protein in spinocerebellar ataxia type 3 (SCA3), has been associated ... more Ataxin-3 (AT3), the disease protein in spinocerebellar ataxia type 3 (SCA3), has been associated with the ubiquitin-proteasome system and transcriptional regulation. Here we report that normal AT3 binds to target DNA sequences in specific chromatin regions of the matrix metalloproteinase-2 (MMP-2) gene promoter and represses transcription by recruitment of the histone deacetylase 3 (HDAC3), the nuclear receptor corepressor (NCoR), and deacetylation of histones bound to the promoter. Both normal and expanded AT3 physiologically interacted with HDAC3 and NCoR in a SCA3 cell model and human pons tissue; however, normal AT3-containing protein complexes showed increased histone deacetylase activity, whereas expanded AT3-containing complexes had reduced deacetylase activity. Consistently, histone analyses revealed an increased acetylation of total histone H3 in expanded AT3-expressing cells and human SCA3 pons. Expanded AT3 lost the repressor function and displayed altered DNA/chromatin binding that was not associated with recruitment of HDAC3, NCoR, and deacetylation of the promoter, allowing aberrant MMP-2 transcription via the transcription factor GATA-2. For transcriptional repression normal AT3 cooperates with HDAC3 and requires its intact ubiquitin-interacting motifs (UIMs), whereas aberrant transcriptional activation by expanded AT3 is independent of the UIMs but requires the catalytic cysteine of the ubiquitin protease domain. These findings demonstrate that normal AT3 binds target promoter regions and represses transcription of a GATA-2dependent target gene via formation of histone-deacetylating repressor complexes requiring its UIM-associated function. Expanded AT3 aberrantly activates transcription via its catalytic site and loses the ability to form deacetylating repressor complexes on target chromatin regions.
Chocolate residues staying behind on the mould surface during chocolate bar manufacture are respo... more Chocolate residues staying behind on the mould surface during chocolate bar manufacture are responsible for production losses, and increased processing costs due to equipment cleaning. This study investigates the determining role of surface energy in chocolate adhesion to the mould substrate and the ease of its demoulding. Four materials (quartz glass, stainless steel, polycarbonate, and Teflon) were investigated as mould substrates. A classical contact angle approach was used for the surface energy determination of mould materials. Chocolate-mould adhesion was measured by a simple separation test between the solidified chocolate and a mould probe using a Texture Analyser. The results demonstrated that surface energy of the mould material is a key determining factor of chocolate-mould interaction and has a significant influence on the adhesion of cocoa butter and dark chocolate to the mould. Further analysis has shown that the electron donor component of the surface energy is the main differentiating factor determining the extent of chocolate adhesion. It is concluded that a high surface energy material is generally not favourable for fabrication of the mould. For clean demoulding, the mould material should have a surface energy below 30 mN m À1 and an electron donor component of the surface energy of approximately 15 mN m À1 .
Traditional chocolate manufacturing relies largely on the experience and skill of the chocolatier... more Traditional chocolate manufacturing relies largely on the experience and skill of the chocolatier. Nowadays, with the replacement of manual processes with automated equipments, it is increasingly important to apply right processing conditions and controlling parameters, such as the time, the temperature, the moisture content, the relative humidity of the surrounding air, etc. This study investigated the influences of these factors during the moulding and cooling stage of chocolate manufacturing process on the ease of demoulding. Adhesion of chocolate to the polycarbonate mould surface was used as a measure for the demoulding properties, and was determined as the force required to separate a flat mould surface from the solidified chocolate sample. The results demonstrated that processing parameters, like temperature, contact time, and the relative humidity of the surrounding environment, have a significant impact on chocolate crystallization and solidification processes and on the adhesion of chocolate to a mould surface. Experimental findings from this work confirmed observations made during commercial chocolate manufacturing.
The objective of this study is to understand how the addition of limonene, a low molecular weight... more The objective of this study is to understand how the addition of limonene, a low molecular weight hydrophobic compound, to chocolate, leads to a decrease in the viscosity of molten chocolate. Chocolate is a fat (cocoa butter) based dispersion of solids (sugar, cocoa and ...
Central Composite Rotatable Design (CCRD) for K = 2 was used to study the combined effects of mul... more Central Composite Rotatable Design (CCRD) for K = 2 was used to study the combined effects of multi-stage heat exchangers for Stages 1 (14-30°C) and 2 (12-28°C) coolant temperatures at constant Stage 3 coolant and holding temperatures during tempering of dark chocolates using laboratory-scale mini-temperer. Quantitative data on chocolate temper index (slope) were obtained for products with varying particle size distribution (PSD) (D 90 of 18, 25, 35 and 50 μm) and fat (30% and 35%) content. Regression models generated using stepwise regression analyses were used to plot response surface curves, to study the tempering behaviour of products. The results showed that both Stage 1 and Stage 2 coolant temperatures had significant linear and quadratic effects on the crystallization behaviour causing wide variations in chocolate temper index during tempering of products with variable PSD and fat content. Differences in fat content exerted the greatest variability in temperature settings of the different zones for attaining well-tempered products. At 35% fat content, changes in PSD caused only slight and insignificant effect on tempering behaviour. No unique set of conditions was found to achieve good temper in dark chocolate with a specified tempering unit. Thus, different combinations of temperatures could be employed between the multi-stage heat exchangers to induce nucleation and growth of stable fat crystal polymorphs during tempering. Variations in tempering outcomes of the dark chocolates were dependent more on the fat content than PSD.
Particle size distribution (PSD) and temper influences on dark chocolate fat crystallization were... more 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 DH 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 DH melt ) of products. Under-tempered chocolate showed widened crystal size distribution (CSD) with significant changes in T end , T index and DH melt of products. Over-tempering caused moderate increases in CSD and melting properties, with significant effect on T end , T index and DH 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 precrystallization of dark chocolate is necessary for the achievement of premium quality products and avoidance of defects in structure and melting character.
International Journal of Food Science and Technology, 2009
Composition in dark chocolate was varied and the effects determined on microstructure, using ligh... more 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.
Fat bloom development and associated changes in microstructure, texture, appearance and melting p... more Fat bloom development and associated changes in microstructure, texture, appearance and melting properties were studied. Dark chocolates varying in particle size (PS) (D 90 of 18, 25, 35 and 50 lm) were processed and pre-crystallised to under-temper regime. Bloom was induced by storing products under ambient conditions (18 ± 2°C, RH 50%) and changes in texture, surface whiteness, gloss and melting properties evaluated on cooling and after every 24 h in storage until reaching asymptotic values. Microstructure of products were characterised during blooming using stereoscopic binocular microscopy. Measurements on texture and surface whiteness showed initial rapid increases with consequential reductions in gloss within the first 96 h, followed by gradually decreasing gradient until reaching asymptotic levels. Storage influenced melting properties (T onset , T end , T peak and DH melt ) in products causing polymorphic transformation from bIV to bVI within 72 h. Micrographs showed similar surface crystalline network structure and inter-particle interactions among products from different PS after tempering, and bloom initiation occurred within 24 h in storage resulting in appearance of both liquid and unstable fat on the surface of products. The unstable fat then re-crystallised during storage into more stable polymorphs and crystal growth was promoted by Ostwald ripening (larger crystals growing at the expense of smaller ones), with the appearance of white crystalline structure which spread gradually throughout the chocolate mass after 96 h. Product containing the largest PS (50 lm) showed the fastest fat bloom rate, with the smallest PS (18 lm) the least, attributed mainly to hydrodynamic forces by capillary action. It was hypothesised that fat bloom development was initiated by capillarity, followed by growth of re-crystallised fat by diffusion across the entire chocolate mass until fully bloomed.
International Journal of Food Science and Technology, 2009
Parameters in chocolate rheology, namely shear viscosity and yield stress, are important in manuf... more 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 (R2 = 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.
Fat crystallisation behaviours in dark chocolates from varying particle size distribution (PSD) (... more Fat crystallisation behaviours in dark chocolates from varying particle size distribution (PSD) (D 90 of 18, 25, 35 and 50 lm) was studied, yielding products from different temper regimes (optimal temper, over-temper and under-temper), and their effects on mechanical properties and appearance evaluated. Microstructures of derived products were determined using stereoscopic binocular microscopy. Wide variations in mechanical properties and appearance were noted in products from different particle size and temper regimes. Particle size (PS) was inversely related with texture and colour, with the greatest effects noted in hardness, stickiness and lightness at all temper regimes. Over-tempering caused significant increases in product hardness, stickiness with reduced gloss and darkening of product surfaces. Under-tempering induced fat bloom in products with consequential quality defects on texture, colour and surface gloss. Micrographs revealed variations in surface and internal crystal network structure and inter-particle interactions among tempered, over-tempered and under-tempered (bloomed) samples. Under-tempering caused whitening of both surface and internal periphery of products with effects on texture and appearance. Thus, attainment of optimal temper regime during pre-crystallisation of dark chocolate was central to the desired texture and appearance as both over-tempering and under-tempering resulted in quality defects affecting mechanical properties and appearance of products.
In dark chocolate, rheological properties during processing are influenced by particle size distr... more In dark chocolate, rheological properties during processing are influenced by particle size distribution (PSD), fat and lecithin contents with consequential effects on finished texture and melting characteristics. Multivariate regression, correlation and principal component analyses (PCA) were used to explore their interrelationships. A 4 × 3 × 2 factorial experiment was conducted with varying PSD [D 90 (90% finer than this size) of 18, 25, 35 and 50 μm], fat (25, 30 and 35%) and lecithin (0.3 and 0.5%). Rheological properties (yield stress and apparent viscosity), textural properties (firmness, index of viscosity and hardness) and melting index (duration) were respectively measured using shear rate-controlled rheometer, TA.HD Plus texture analyzer and differential scanning calorimetry. The PSD, fat and lecithin contents significantly influenced all rheological, textural properties and some melting characteristics. Increasing particles sizes reduced yield stress, apparent viscosity, firmness, index of viscosity, hardness and melting index of products with greatest influence with 25% fat and 0.3% lecithin, reduced with increasing fat and lecithin contents. There were high correlation (r = 0.78–0.99) and regression coefficients (R 2 = 0.59–0.99) among the rheological, textural and melting index indicating their high inter-relationships. In PCA, the rheological, textural and melting index accounted for >95% variance in the data.
Particle size distribution (PSD) and composition in dark chocolate were varied and their effects ... more Particle size distribution (PSD) and composition in dark chocolate were varied and their effects on textural properties of molten and tempered chocolates determined using a TA.HD Plus Texture Analyzer. Surface colour was evaluated in terms of CIELAB parameters L*, C* and h°using a HunterLab Miniscan Colorimeter. Compositional parameters for particle size distribution were [D 90 (>90% finer) of 18 lm, 25 lm, 35 lm and 50 lm], fat (25%, 30% and 35%) and lecithin (0.3% and 0.5%) contents. Results showed that PSD, fat and lecithin content significantly (P 6 0.05) influenced the textural parameters with significant interactions among factors. Particle size was inversely correlated with firmness (1235-173 g), consistency (50,410-7029 g s), cohesiveness (1594-262 g), index of viscosity (5737-1099 g s) and hardness (7062-5546 g) with chocolates containing 25% fat and 0.3% lecithin. With higher fat and lecithin contents, PSD influence was reduced. PSD and fat concentration inversely influenced all colour measurements (L*, C* and h°) of samples. High correlations (r = 0.71-1.00, P < 0.001) were observed between texture parameters and colour. It was concluded that PSD, fat and lecithin contents and their interactions were central to changes in textural properties and appearance during processing of dark chocolates.
Ataxin-3 (AT3), the disease protein in spinocerebellar ataxia type 3 (SCA3), has been associated ... more Ataxin-3 (AT3), the disease protein in spinocerebellar ataxia type 3 (SCA3), has been associated with the ubiquitin-proteasome system and transcriptional regulation. Here we report that normal AT3 binds to target DNA sequences in specific chromatin regions of the matrix metalloproteinase-2 (MMP-2) gene promoter and represses transcription by recruitment of the histone deacetylase 3 (HDAC3), the nuclear receptor corepressor (NCoR), and deacetylation of histones bound to the promoter. Both normal and expanded AT3 physiologically interacted with HDAC3 and NCoR in a SCA3 cell model and human pons tissue; however, normal AT3-containing protein complexes showed increased histone deacetylase activity, whereas expanded AT3-containing complexes had reduced deacetylase activity. Consistently, histone analyses revealed an increased acetylation of total histone H3 in expanded AT3-expressing cells and human SCA3 pons. Expanded AT3 lost the repressor function and displayed altered DNA/chromatin binding that was not associated with recruitment of HDAC3, NCoR, and deacetylation of the promoter, allowing aberrant MMP-2 transcription via the transcription factor GATA-2. For transcriptional repression normal AT3 cooperates with HDAC3 and requires its intact ubiquitin-interacting motifs (UIMs), whereas aberrant transcriptional activation by expanded AT3 is independent of the UIMs but requires the catalytic cysteine of the ubiquitin protease domain. These findings demonstrate that normal AT3 binds target promoter regions and represses transcription of a GATA-2dependent target gene via formation of histone-deacetylating repressor complexes requiring its UIM-associated function. Expanded AT3 aberrantly activates transcription via its catalytic site and loses the ability to form deacetylating repressor complexes on target chromatin regions.
Chocolate residues staying behind on the mould surface during chocolate bar manufacture are respo... more Chocolate residues staying behind on the mould surface during chocolate bar manufacture are responsible for production losses, and increased processing costs due to equipment cleaning. This study investigates the determining role of surface energy in chocolate adhesion to the mould substrate and the ease of its demoulding. Four materials (quartz glass, stainless steel, polycarbonate, and Teflon) were investigated as mould substrates. A classical contact angle approach was used for the surface energy determination of mould materials. Chocolate-mould adhesion was measured by a simple separation test between the solidified chocolate and a mould probe using a Texture Analyser. The results demonstrated that surface energy of the mould material is a key determining factor of chocolate-mould interaction and has a significant influence on the adhesion of cocoa butter and dark chocolate to the mould. Further analysis has shown that the electron donor component of the surface energy is the main differentiating factor determining the extent of chocolate adhesion. It is concluded that a high surface energy material is generally not favourable for fabrication of the mould. For clean demoulding, the mould material should have a surface energy below 30 mN m À1 and an electron donor component of the surface energy of approximately 15 mN m À1 .
Traditional chocolate manufacturing relies largely on the experience and skill of the chocolatier... more Traditional chocolate manufacturing relies largely on the experience and skill of the chocolatier. Nowadays, with the replacement of manual processes with automated equipments, it is increasingly important to apply right processing conditions and controlling parameters, such as the time, the temperature, the moisture content, the relative humidity of the surrounding air, etc. This study investigated the influences of these factors during the moulding and cooling stage of chocolate manufacturing process on the ease of demoulding. Adhesion of chocolate to the polycarbonate mould surface was used as a measure for the demoulding properties, and was determined as the force required to separate a flat mould surface from the solidified chocolate sample. The results demonstrated that processing parameters, like temperature, contact time, and the relative humidity of the surrounding environment, have a significant impact on chocolate crystallization and solidification processes and on the adhesion of chocolate to a mould surface. Experimental findings from this work confirmed observations made during commercial chocolate manufacturing.
The objective of this study is to understand how the addition of limonene, a low molecular weight... more The objective of this study is to understand how the addition of limonene, a low molecular weight hydrophobic compound, to chocolate, leads to a decrease in the viscosity of molten chocolate. Chocolate is a fat (cocoa butter) based dispersion of solids (sugar, cocoa and ...
Central Composite Rotatable Design (CCRD) for K = 2 was used to study the combined effects of mul... more Central Composite Rotatable Design (CCRD) for K = 2 was used to study the combined effects of multi-stage heat exchangers for Stages 1 (14-30°C) and 2 (12-28°C) coolant temperatures at constant Stage 3 coolant and holding temperatures during tempering of dark chocolates using laboratory-scale mini-temperer. Quantitative data on chocolate temper index (slope) were obtained for products with varying particle size distribution (PSD) (D 90 of 18, 25, 35 and 50 μm) and fat (30% and 35%) content. Regression models generated using stepwise regression analyses were used to plot response surface curves, to study the tempering behaviour of products. The results showed that both Stage 1 and Stage 2 coolant temperatures had significant linear and quadratic effects on the crystallization behaviour causing wide variations in chocolate temper index during tempering of products with variable PSD and fat content. Differences in fat content exerted the greatest variability in temperature settings of the different zones for attaining well-tempered products. At 35% fat content, changes in PSD caused only slight and insignificant effect on tempering behaviour. No unique set of conditions was found to achieve good temper in dark chocolate with a specified tempering unit. Thus, different combinations of temperatures could be employed between the multi-stage heat exchangers to induce nucleation and growth of stable fat crystal polymorphs during tempering. Variations in tempering outcomes of the dark chocolates were dependent more on the fat content than PSD.
Particle size distribution (PSD) and temper influences on dark chocolate fat crystallization were... more 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 DH 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 DH melt ) of products. Under-tempered chocolate showed widened crystal size distribution (CSD) with significant changes in T end , T index and DH melt of products. Over-tempering caused moderate increases in CSD and melting properties, with significant effect on T end , T index and DH 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 precrystallization of dark chocolate is necessary for the achievement of premium quality products and avoidance of defects in structure and melting character.
International Journal of Food Science and Technology, 2009
Composition in dark chocolate was varied and the effects determined on microstructure, using ligh... more 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.
Fat bloom development and associated changes in microstructure, texture, appearance and melting p... more Fat bloom development and associated changes in microstructure, texture, appearance and melting properties were studied. Dark chocolates varying in particle size (PS) (D 90 of 18, 25, 35 and 50 lm) were processed and pre-crystallised to under-temper regime. Bloom was induced by storing products under ambient conditions (18 ± 2°C, RH 50%) and changes in texture, surface whiteness, gloss and melting properties evaluated on cooling and after every 24 h in storage until reaching asymptotic values. Microstructure of products were characterised during blooming using stereoscopic binocular microscopy. Measurements on texture and surface whiteness showed initial rapid increases with consequential reductions in gloss within the first 96 h, followed by gradually decreasing gradient until reaching asymptotic levels. Storage influenced melting properties (T onset , T end , T peak and DH melt ) in products causing polymorphic transformation from bIV to bVI within 72 h. Micrographs showed similar surface crystalline network structure and inter-particle interactions among products from different PS after tempering, and bloom initiation occurred within 24 h in storage resulting in appearance of both liquid and unstable fat on the surface of products. The unstable fat then re-crystallised during storage into more stable polymorphs and crystal growth was promoted by Ostwald ripening (larger crystals growing at the expense of smaller ones), with the appearance of white crystalline structure which spread gradually throughout the chocolate mass after 96 h. Product containing the largest PS (50 lm) showed the fastest fat bloom rate, with the smallest PS (18 lm) the least, attributed mainly to hydrodynamic forces by capillary action. It was hypothesised that fat bloom development was initiated by capillarity, followed by growth of re-crystallised fat by diffusion across the entire chocolate mass until fully bloomed.
International Journal of Food Science and Technology, 2009
Parameters in chocolate rheology, namely shear viscosity and yield stress, are important in manuf... more 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 (R2 = 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.
Fat crystallisation behaviours in dark chocolates from varying particle size distribution (PSD) (... more Fat crystallisation behaviours in dark chocolates from varying particle size distribution (PSD) (D 90 of 18, 25, 35 and 50 lm) was studied, yielding products from different temper regimes (optimal temper, over-temper and under-temper), and their effects on mechanical properties and appearance evaluated. Microstructures of derived products were determined using stereoscopic binocular microscopy. Wide variations in mechanical properties and appearance were noted in products from different particle size and temper regimes. Particle size (PS) was inversely related with texture and colour, with the greatest effects noted in hardness, stickiness and lightness at all temper regimes. Over-tempering caused significant increases in product hardness, stickiness with reduced gloss and darkening of product surfaces. Under-tempering induced fat bloom in products with consequential quality defects on texture, colour and surface gloss. Micrographs revealed variations in surface and internal crystal network structure and inter-particle interactions among tempered, over-tempered and under-tempered (bloomed) samples. Under-tempering caused whitening of both surface and internal periphery of products with effects on texture and appearance. Thus, attainment of optimal temper regime during pre-crystallisation of dark chocolate was central to the desired texture and appearance as both over-tempering and under-tempering resulted in quality defects affecting mechanical properties and appearance of products.
In dark chocolate, rheological properties during processing are influenced by particle size distr... more In dark chocolate, rheological properties during processing are influenced by particle size distribution (PSD), fat and lecithin contents with consequential effects on finished texture and melting characteristics. Multivariate regression, correlation and principal component analyses (PCA) were used to explore their interrelationships. A 4 × 3 × 2 factorial experiment was conducted with varying PSD [D 90 (90% finer than this size) of 18, 25, 35 and 50 μm], fat (25, 30 and 35%) and lecithin (0.3 and 0.5%). Rheological properties (yield stress and apparent viscosity), textural properties (firmness, index of viscosity and hardness) and melting index (duration) were respectively measured using shear rate-controlled rheometer, TA.HD Plus texture analyzer and differential scanning calorimetry. The PSD, fat and lecithin contents significantly influenced all rheological, textural properties and some melting characteristics. Increasing particles sizes reduced yield stress, apparent viscosity, firmness, index of viscosity, hardness and melting index of products with greatest influence with 25% fat and 0.3% lecithin, reduced with increasing fat and lecithin contents. There were high correlation (r = 0.78–0.99) and regression coefficients (R 2 = 0.59–0.99) among the rheological, textural and melting index indicating their high inter-relationships. In PCA, the rheological, textural and melting index accounted for >95% variance in the data.
Particle size distribution (PSD) and composition in dark chocolate were varied and their effects ... more Particle size distribution (PSD) and composition in dark chocolate were varied and their effects on textural properties of molten and tempered chocolates determined using a TA.HD Plus Texture Analyzer. Surface colour was evaluated in terms of CIELAB parameters L*, C* and h°using a HunterLab Miniscan Colorimeter. Compositional parameters for particle size distribution were [D 90 (>90% finer) of 18 lm, 25 lm, 35 lm and 50 lm], fat (25%, 30% and 35%) and lecithin (0.3% and 0.5%) contents. Results showed that PSD, fat and lecithin content significantly (P 6 0.05) influenced the textural parameters with significant interactions among factors. Particle size was inversely correlated with firmness (1235-173 g), consistency (50,410-7029 g s), cohesiveness (1594-262 g), index of viscosity (5737-1099 g s) and hardness (7062-5546 g) with chocolates containing 25% fat and 0.3% lecithin. With higher fat and lecithin contents, PSD influence was reduced. PSD and fat concentration inversely influenced all colour measurements (L*, C* and h°) of samples. High correlations (r = 0.71-1.00, P < 0.001) were observed between texture parameters and colour. It was concluded that PSD, fat and lecithin contents and their interactions were central to changes in textural properties and appearance during processing of dark chocolates.
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Papers by Joselio Vieira