Image analysis of changes in surface color of chocolate

Blooming or the migration of fat to the surface of chocolate results in color changes and development of non-uniform color patterns. These phenomena were assessed during storage of milk chocolate tablets (cycling temp. between 16 and 28 °C for 52 days) by a computer vision system and image analysis. Eight features were extracted from images (L*, a* and b* values, whiteness index, chroma, hue, % bloom and energy of Fourier). Major changes occurred after day 36 of storage, coincidental with visual perception. Initially, white specks emerged on the brown background but were superseded by the development of a whitish color extending over most of the surface. L*, whiteness index, a* and chroma correlated well with values taken with a commercial colorimeter (R² > 0.70). Changes in image texture (energy of Fourier) followed a similar trend as color changes. The sequential forward selection strategy allowed correct classification of 97.8% of samples into four classes with only five features. The computer vision system has the capability to quantify overall changes as well as particular features over the whole chocolate surface thus enabling customization and standardization for quality assessment.     

Enzymatic browning in sliced and puréed avocado: A fractal kinetic study

Modelling of browning is essential to evaluate the effectiveness of the processes applied to obtain fresh-appearance foods and also to determine their shelf life. Computer vision and the fractal kinetic method were used to quantify browning in three avocado cultivars. Samples (avocado slices and purée) were stored at 4 °C and surface images were captured in the tiff format. Browning kinetic was derived from images using the L^∗ mean method and the fractal method. In another experiment, inhibitor kinetic was also quantified, using the polyphenol oxidase activity method (in purée samples) with 0.1%, 0.5% and 1% of sodium bisulfite. In the results for avocado slices, kinetic rate derived by the fractal kinetic method was higher than that obtained with the L^∗ mean method, but the opposite was observed when the avocado was pulping (avocado purée). Kinetic quantified by the fractal method was similarly inhibited by bisulfite, when compared with the L^∗ mean value or PPO activity value methods. In general, the fractal method can be used to record browning kinetic and to discriminate between avocado cultivars, initial structural state of the sample (slice or purée), or in experiments using browning inhibitors.     

UTILITY OF CIE TRISTIMULUS SYSTEM IN MEASURING THE OBJECTIVE CRUMB COLOR OF HIGH-FIBER TOAST BREAD FORMULATIONS

The major objectives of this study were to develop high‐fiber toast bread formulations with lighter crumb color and to evaluate the CIE tristimulus system to measure the color of crumb as affected by the addition of various flour mill fractions. The optimized straight‐dough bread making method (AACC method 10‐10B) was used for conducting the baking trials. CIE L* a* b* values of the crumb were measured. Additional color attributes, (whiteness value, redness index (RI), saturation index (SI) and total color difference (ΔE), were calculated from these L* a* b* values. Compared with flour samples, the germ and bran fractions had significantly lower CIE L* a* b* and whiteness values, but higher redness and saturation indices, indicating darker color and hue for the latter. Test bread samples having up to 30% bran and 10% germ, were lighter in crumb color than the control whole wheat flour bread. It was concluded that high‐fiber toast bread, with lighter crumb color than whole wheat flour bread, can be produced by using white flour, and equal proportions of coarse and fine bran at 20%, germ at 5%, and sodium stearoyl‐2‐lactylate at 0.5% levels. The CIE L*a* b* tristimulus system can effectively be utilized for distinguishing crumb color variations in toast bread samples.     

Surface structure and composition of fresh and bloomed chocolate analysed using X-ray photoelectron spectroscopy, cryo-scanning electron microscopy and environmental scanning electron microscopy

Bloom on chocolate is an unsightly surface condition resulting in a white, powdery appearance that consumers interpret as a sign of poor quality. Bloom results from incorrect processing or storage. Two innovative methods have been developed, and used in conjunction, to investigate the morphology and composition of bloomed chocolate.Environmental scanning electron microscopy (ESEM) was used to image the morphology of the surface of fresh and bloomed chocolate and to observe the changes in morphology, in real time, during heating and cooling. The nodular morphology of sugar bloom was easily distinguished from the blade like crystals of fat bloom. Surface details for the fat blades indicated an extrusion mechanism during their formation on the chocolate surface.“Cold stage” X-Ray Photoelectron Spectroscopy (XPS) was used to analyse the surface composition of fresh and bloomed samples. The carbon species present in the bloom on poorly tempered chocolate were a combination of CH₂, C-OH, OC-OH and O-C-O groups indicating a mixture of sugar and fat bloom. Conversely the species present on bloomed, well tempered chocolate comprised only CH₂, C-OH, OC-OH indicating the bloom was comprised of fat (from cocoa butter) and no sugar.     

Influence of lactic acid ester on chocolate quality

Influence of concentration of emulsifier Lactem P 22 (lactic acid ester of monodiglyceride) as blooming inhibitor on the quality and fat bloom stability of laboratory made samples of chocolate was investigated. This ingredient was added during the pre-crystallization process of chocolate mass. The pre-crystallization was performed in the laboratory crystallizer modified Brabender pharinograph, where the rheological characteristics of the pre-crystallized fluid chocolate mass were measured. The experiments were performed according to the factorial plan 3² (two factors on three levels). Statistical results processing was performed according to the Response Surface Methodology. Physics characteristics of chocolate—hardness and lightness—were obtained by instrumental methods. The results has shown that Lactem P 22 improve fat bloom stability of chocolate samples but decrease sensory quality of chocolate. Better sensory quality of chocolate was achieved with combination of the crystallization promoter—Dynasan 118. The best sensory quality of chocolate has been obtained with 0.5% Dynasan 118 and 1 and 2% Lactem P 22. Samples of chocolate which was pre-crystallized on 23°C and with 3% Lactem P 22, showed the highest fat bloom stability.     

Influence of high-melting milk fat fraction on quality and fat bloom stability of chocolate

The aim of this paper was to define the optimal concentration of a high-melting milk fat fraction with a suitable precrystallization temperature time regime in order to obtain chocolate which would have satisfactory sensory characteristics and an increased fat bloom stability. The precrystallization was performed in a laboratory crystallizer, that is in a modified Brabender pharinograph, which measures the rheological characteristics of the precrystallized fluid chocolate mass with a milk fat fraction. The experiments were performed according to the factorial plan 3² (two factors on three levels). Hardness as well as solid fat content of chocolate was measured by instrumental methods. The optimal sensory quality of chocolate was achieved by adding 1–3% of the milk fat fraction and under the 25 °C precrystallization temperature. These samples of chocolate showed the highest fat bloom stability.     

Controlling fat bloom formation in chocolate – Impact of milk fat on microstructure and fat phase crystallisation

The partial replacement of cocoa butter (CB) with milk fat (MF) strongly influences micro-scale topographic evolution and fat phase crystallisation in milk chocolate. Adding MF reduces the incidence of large surface crystals and the number and diameter of amorphous, welled CB deposits (‘cones’), with a concurrent decrease in initial surface roughness (p < 0.05) and rate of surface coarsening. Presence of MF also slows the solidification of the cones into disorganised crystalline masses. Finally, MF reduces the initial solid fat content, and slows the rate of change in whiteness index, as well as the form V to VI polymorphic transition. Fat crystal growth is accelerated by repeated temperature-cycling (26–29 °C) compared to isothermal conditioning (26 °C). However, cone hardening occurs more rapidly when isothermally-stored. Irrespective of fat composition and storage conditions, fat crystal growth, welling and ultimately fat bloom begin only at specific locations on the chocolate surface, suggesting that chocolate’s microstructural heterogeneity is responsible for distinct surface fat crystallisation pathways.     

巧克力起霜问题探讨

如何有效防止起霜是巧克力制造业需待解决问题,该文比较全面分析巧克力起霜原因,机理, 并提出相应延缓巧克力起霜方法。     

巧克力“白霜”的解决方案

<正>巧克力风味独特、口感好,颇受人们的喜爱。随着巧克力制品消费量的增加,其质量问题也越来越受到各方的关注。其中巧克力起白霜是巧克力产业的世界性难题。白霜花是指加工、贮存、销售过程中,巧克力表面均一发白(酷似秋霜)或起凹凸不平的花斑点,甚至全部变成灰白色而失去光泽。外观使顾客误以为发霉而令人难以接受。严重时,内部组织呈干砂粒状,失去坚脆、断而有声、入口即化,凉爽润滑、细腻而不糊口等特征, 食似嚼蜡,失去商品价值。     

Rejection Thresholds in Solid Chocolate‐Flavored Compound Coating

Abstract: Classical detection thresholds do not predict liking, as they focus on the presence or absence of a sensation. Recently however, Prescott and colleagues described a new method, the rejection threshold, where a series of forced choice preference tasks are used to generate a dose‐response function to determine hedonically acceptable concentrations. That is, how much is too much? To date, this approach has been used exclusively in liquid foods. Here, we determined group rejection thresholds in solid chocolate‐flavored compound coating for bitterness. The influences of self‐identified preferences for milk or dark chocolate, as well as eating style (chewers compared to melters) on rejection thresholds were investigated. Stimuli included milk chocolate‐flavored compound coating spiked with increasing amounts of sucrose octaacetate, a bitter and generally recognized as safe additive. Paired preference tests (blank compared to spike) were used to determine the proportion of the group that preferred the blank. Across pairs, spiked samples were presented in ascending concentration. We were able to quantify and compare differences between 2 self‐identified market segments. The rejection threshold for the dark chocolate preferring group was significantly higher than the milk chocolate preferring group (P= 0.01). Conversely, eating style did not affect group rejection thresholds (P= 0.14), although this may reflect the amount of chocolate given to participants. Additionally, there was no association between chocolate preference and eating style (P= 0.36). Present work supports the contention that this method can be used to examine preferences within specific market segments and potentially individual differences as they relate to ingestive behavior. Practical Application: This work makes use of the rejection threshold method to study market segmentation, extending its use to solid foods. We believe this method has broad applicability to the sensory specialist and product developer by providing a process to identify how much is too much when formulating products, even in the context of specific market segments. We illustrate this in solid chocolate‐flavored compound coating, identifying substantial differences in the amount of acceptable bitterness in those who prefer milk chocolate compared to dark chocolate. This method provides a direct means to answer the question of how much is too much.     

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.     

A micromechanical based finite element model approach to accurately predict the effective thermal properties of micro-aerated chocolate

Micro-aeration is a method to modify the sensorial attributes of chocolate but also affects the material properties of chocolate, which in turn, determine its material response during manufacturing and oral processes. This study aims to define the effect of micro-aeration on the thermal properties of chocolate by considering the changes of chocolate microstructure due to micro-aeration. Micro-aeration was found to alter the chocolate microstructure creating a layer of a third phase at the porous interfaces, which is argued to consist of cocoa butter of higher melting properties. A multiscale Finite Element Model is developed, which was confirmed by macroscale heat transfer measurements, to parametrically simulate the structural changes of micro-porous chocolates at the microscale level and estimate their effective properties, such as thermal conductivity and specific heat capacity. The developed multiscale computational model simulates the porous chocolate as a two-phase (chocolate- pores) or three-phase material (chocolate-cocoa butter layer- pores). The investigation identified a new, complex transient thermal mechanism that controls the behaviour of micro-aerated chocolate during melting and solidification. The results showed a maximum 13% reduction of k_eff and 15% increase of C_peff with 15% micro-aeration resulting to a slower transient heat transfer through the micro-aerated chocolate. The reason is that the micro-aerated chocolate can store a larger amount of thermal energy than its solid counterpart. This effect slows down the transient heat transfer rate in the chocolate and modifies melting/solidification rate and impacts sensorial attributes during oral processing and cooling during manufacturing.     

Interactions of caseins with phenolic acids found in chocolate

To investigate the interactions between caseins and phenolic acids, such as the ones present in chocolate, casein was incubated with protocatechuic acid or p-coumaric acid at 55 °C. In addition, casein was isolated from chocolate and the phenolic compounds within these caseins were quantified. Electrophoresis results revealed that casein–phenolic interactions were induced by incubation; minor aggregation of casein subunits was observed after incubation of casein with protocatechuic acid. Minor aggregation of casein isolated from milk chocolate was also observed. In vitro hydrolysis of casein control, casein–protocatechuic acid, casein–p-coumaric acid, caseins isolated from milk chocolate and white chocolate using trypsin showed degree of hydrolysis of 19.3, 18.6, 17.7, 10.4 and 17.8% respectively. The presence of protocatechuic acid and p-coumaric acid in the model system and the presence of phenolic compounds in milk chocolate, in addition to the structural changes occurring during processing, affected the peptide profiles of casein hydrolysates.     

Application of various methods for determination of the color of cocoa beans roasted under variable process parameters

Cocoa beans of Forastero variety from Togo were subjected to roasting under either constant or variable process parameters. The variable process parameters were roasting air flow rate, temperature and relative humidity. The color of roasted cocoa beans was determined by pigment extraction under various conditions followed by either their spectrophotometric assays or CIE L*a*b measurements. Also the Maillard compounds index and total polyphenols content correlated with progress of the browning of beans were determined. It was found that an increase in the roasting air relative humidity stimulated formation of brown pigments, while elevated temperature caused worsening of color parameters of roasted cocoa beans. The most suitable method of color characterization of roasted cocoa beans was found to be pigments extraction combined with either separation of their fractions or CIE L*a*b measurements. These assays revealed that cocoa beans roasted under variable roasting air flow rate were characterized by improved color parameters. The relatively simple and inexpensive CIE L*a*b measurements ensured fast analysis of color parameters, while total polyphenols in roasted cocoa beans were quickly estimated by using F–C reagent. Furthermore, quantification of melanoid pigments in roasted cocoa beans can be based on determination of the index of nonenzymatic browning products content, which is relatively simple and inexpensive.     

RHEOLOGY OF DIFFERENT FORMULATIONS OF MILK CHOCOLATE AND THE EFFECT ON COATING THICKNESS

This work characterized the flow properties and investigated the effect of grind, emulsifier type and emulsifier level on the coating thickness of milk chocolate. Rheological properties were characterized using a concentric cylinder viscometer according to the method recommended by the International Confectionery Association. The thickness of the chocolate on dip‐coated acrylic plates was obtained by a gravimetric method. A three‐way analysis of variance was performed for the coating thickness. All three factors were significant; the thickness of the chocolate coating was greater for fine grind, soy lecithin for emulsifier and for low concentrations of emulsifier. The thicknesses were well predicted using the model with the Casson model parameters from the rheological characterization.     

Color improvement by titanium dioxide and its effect on gelation and texture of proteins recovered from whole fish using isoelectric solubilization/precipitation

Whiteness is a critical attribute for restructured fish products such as surimi seafood. However, the whiteness of gels made from proteins recovered from fish processing by-products or whole fish using isoelectric solubilization/precipitation is poor. The by-products and whole fish contain bones, scales, skin, etc. that affect gel color. Therefore, whiteness needs to be improved if marketable products are to be developed from recovered proteins. The objectives of this study were to determine effects of titanium dioxide (TiO₂) on: (1) color; (2) texture; and (3) viscoelasticity (G′) of gels made from isolated carp proteins and Alaska pollock surimi. Carp proteins were recovered with isoelectric solubilization/precipitation. TiO₂ was added to carp proteins at 0-0.5 g/100 g. TiO₂ was not added to surimi. Due to much higher (P < 0.05) yellowness (b^∗) and lower (P < 0.05) lightness (L^∗), the whiteness of carp gels without TiO₂ was lower (P < 0.05) than surimi gels. TiO₂ at ≥ 0.2 g/100 g resulted in better (P < 0.05) whiteness of carp gels than surimi gels without chalky and artificially white appearance. TiO₂ did not affect texture or viscoelasticity. This research demonstrates that whiteness of restructured fish products based on proteins recovered from whole fish via isoelectric solubilization/precipitation can be similar to the whiteness of surimi seafood.     

Color Evaluation in Raw, Baked and Smoked Flesh of Rainbow Trout (Onchorhynchus mykiss) Fed Astaxanthin or Canthaxanthin

Color of rainbow trout (Onchorynchus mykiss) was investigated using sensory and instrumental analysis. When judged in pairs with equal carotenoid concentration, astaxanthin caused less whiteness, higher chromaticity and more red hue of trout flesh than canthaxanthin. Sensory assessed whiteness, chromaticity and red hue significantly correlated with instrumental values for lightness, chromaticity and hue [CIE (1976) L*a*b* and H(°)_ab]. Multivariate regression analysis improved the predictability for all sensory variables compared with univariate analysis. Prediction of carotenoid concentration from instrumental values was better for astaxanthin than for canthaxanthin.     

Photo-scanning colorimetry of wood and transparent wood coatings

Although conventional spectrophotometers are well-known to give very accurate and reproducible measuring results of the wood surface colour, the areal resolution of this method is limited due to the fixed aperture size. In this study, the applicability of a colour calibrated flatbed scanner for areal-resolved colorimetry was investigated. For this purpose, the colorimetric values of several wood species calculated from images of a colour calibrated photo-scanner were correlated with those obtained by a conventional spectrophotometer. Further, this method was used to evaluate the discoloration of earlywood and latewood of Siberian larch (Larix sibirica) during Xenon arc exposure as a demonstration of the potential application of this method. In addition, an investigation concerning the possibility of image analysis for the evaluation of the colour change as a consequence of the application of transparent coatings was done. Good correlation among the measured methods could be found by applying relative colour values ΔL* Δa*, Δb* and ΔE*, whereas absolute colour values L*, a* and b* obtained rather weak correlations. The investigation of the relative discoloration of earlywood and latewood of Siberian larch showed a higher amount of discoloration in the earlywood. The investigation concerning the colour change induced by the application of transparent coatings showed that it is possible to evaluate the discoloration by the coating for earlywood and latewood separately. This could be the basis for a more quantitative comparison of quality parameters of coatings like the visual contrast enhancement effect, known as wet-look or “Anfeuerung” of transparent coatings. It was concluded that when evaluating colour changes on wood the use of a calibrated photo-scanner is a valuable addition to conventional spectrophotometry.     

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.     

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.