EFFECTS OF CONCHING TIME AND INGREDIENTS ON PREFERENCE OF MILK CHOCOLATE

The objective of this study is to determine how the conching time and the quantity of sucrose, lecithin, cocoa butter and whole milk powder affect consumer preference for milk chocolate. Untrained panelists performed a sensory study consisting of acceptability, preference and attribute intensity. Longer conching time produced significantly smoother chocolate with smaller particle size. The longest conche times had the smallest particle size and were the most mouthcoating. There was no change in flavor with conching. The longer conche times were preferred. Panelists preferred higher sucrose levels, and increasing sucrose decreased bitterness and increased chocolate flavor. Increasing lecithin increased smoothness, but less lecithin was preferred, possibly due to off-flavors at high levels of lecithin. Increasing cocoa butter yielded softer chocolate but did not affect bitterness. Panelists preferred 10% over higher levels of cocoa butter. More milk powder produced smoother chocolate with more caramel flavor and was preferred.

PRACTICAL APPLICATIONS

The perceived quality of milk chocolate is affected by conching time, sucrose, lecithin, cocoa butter and whole milk powder. Texture was affected the most by conching, milk powder, lecithin and cocoa butter. Flavor was affected the most by milk powder and sugar. The only variable that did not affect acceptability and preference of milk chocolate was time for underconched samples. While this study did not determine the optimum conditions for milk chocolate, the most preferred and/or acceptable samples were conched for at least 12 h, had 35 to 50% sucrose, 0–0.5% lecithin, 5–10% cocoa butter and 13–30% milk powder.     

Fast conching for milk chocolate

The objective of the study was to shorten the conventional conching process for milk chocolate, which still takes many hours, in order to increase productivity. Due to recent findings and to progress made in raw material treatment, a hypothesis was proposed: that flavour development in the conch could be less important for milk chocolate than it certainly is for dark chocolate. Other functions of conching, like water removal and fat covering of particles, could be achieved faster by using drier raw materials and by machines applying more shear force. For the experiments, a conventional process (taking 5 hours) was condensed into 30–90 minutes. In screening trials various flake pre-drying techniques were also tested. Samples produced were analysed for particle size and flow properties, as well as by a trained sensory panel. Results from the experimental design showed best results at 60–90 minutes conching time. Probably the procedures for flake pre-drying had little or no influence under the conditions used. Verification trials compared the fast conching procedure to the standard process using two different recipes. No relevant differences in physical or sensory properties were found between samples from standard and 90-minute-fast-conching, proving that under favourable conditions conching times for milk chocolates can be drastically reduced without negative impact on product properties and perception.     

OBSERVATIONS OF CHOCOLATE DURING CONCHING BY SCANNING ELECTRON MICROSCOPY AND VISCOMETRY

Dark semi-sweet chocolate samples, obtained at various times during conching, were cooled and prepared for examination by scanning electron microscopy (SEM) in an attempt to observe structural changes during conching. In addition, ingredient mixtures containing known amounts of cocoa solids, microcrystalline cellulose, starch, sucrose and lecithin were studied to correctly identify the components of chocolate. Pulverized sucrose particles were easily characterized by their smooth surfaces and heterogeneous shapes. Defatted chocolate liquor was rougher in appearance and smaller in size than sucrose. Cellular detail of the cocoa bean was evident in liquor even after the disruptive effect of refining. Lecithin, when added to liquor-sugar and cocoa butter-sugar mixtures, had a remarkable and rapid effect in reducing three-dimensional structure. When processed chocolates from four different conches were examined by SEM, little or no differences were observed in the size or shape of the sugar or liquor particles as conching proceeded. Surface smoothening, however, was noted and attributed to the homogenization or spreading of cocoa butter during conching. When lecithin was added to chocolate during conching the surfaces were reduced and appeared to flatten. The effect of lecithin in reducing surface tension was also supported by viscometry. Viscometric measurements taken at this time showed that the increase in fluidity was accompanied by a sharp and rapid decrease in plastic viscosity.     

Impact of starter cultures and fermentation techniques on the volatile aroma and sensory profile of chocolate

The sensory quality of chocolate is widely determined by the qualitative and quantitative composition of volatile compounds resulting from microbial metabolism during fermentation, and Maillard reactions taking place during drying, roasting and conching. The influence of applying mixed starter cultures on the formation of flavour precursors, composition of volatile aroma compounds and sensory profile was investigated in cocoa inoculated with cultures encompassing a highly aromatic strain of Pichia kluyveri or a pectinolytic strain of Kluyveromyces marxianus, and compared to commercially fermented heap and tray cocoa. Although only minor differences in the concentration of free amino acids and reducing sugars was measured, identification and quantification by dynamic headspace gas chromatography–mass spectrometry (HS/GC–MS) revealed pronounced differences in the composition of volatiles in roasted cocoa liquors and finished chocolates. 19 of the 56 volatile compounds identified in the chocolates were found in significantly higher amounts in the tray fermented sample, whilst significantly higher amounts of 2-methoxyphenol was measured in the two inoculated chocolates. The P. kluyveri inoculated chocolate was characterized by a significantly higher concentration of phenylacetaldehyde and the K. marxianus inoculated chocolate by significantly higher amounts of benzyl alcohol, phenethyl alcohol, benzyl acetate and phenethyl acetate compared to a spontaneously fermented control. Sensory profiling described the heap and tray fermented chocolates as sweet with cocoa and caramel flavours, whilst the inoculated chocolates were characterized as fruity, acid and bitter with berry, yoghurt and balsamic flavours. The choice of fermentation technique had the greatest overall impact on the volatile aroma and sensory profile, but whilst the application of starter cultures did affect the volatile aroma profile, differences were too small to significantly change consumer perception of the chocolates as compared to a spontaneously fermented control.     

Fermentation of cocoa beans: influence of microbial activities and polyphenol concentrations on the flavour of chocolate

BACKGROUND: Spontaneous cocoa bean fermentation is characterised by a succession of microbial activities. Cocoa flavour precursors are developed during fermentation and drying of cocoa beans. Polyphenols and alkaloids contribute to astringency and bitterness of cocoa and chocolate. RESULTS: Population dynamics, metabolite target analyses, and chocolate production were performed for seven independent spontaneous cocoa bean heap fermentations in Ghana. Although the same micro‐organisms were involved in these heaps, carried out at different farms or in different seasons, heap temperatures and microbial metabolite concentrations were different. This could be due to heterogeneity and size of the heaps, but was mainly ascribed to microbial variability. Indeed, differences in microbial activity could be linked with the flavour of chocolates made from the corresponding dried, fermented cocoa beans. Whereas the polyphenol and alkaloid contents of cocoa beans were crop‐ and heap‐dependent, epicatechin and theobromine levels decreased during fermentation due to diffusion out of the bean cotyledons and polyphenol oxidation and condensation. Residual levels were responsible for the degree of bitterness of the final chocolates. CONCLUSION: Differences in microbial activities between different heap fermentations can result in dried fermented cocoa beans and chocolates with different flavour characteristics. Hence, fermentation control may direct the flavour of chocolate. Copyright © 2008 Society of Chemical Industry     

Factors contributing to the variation in the volatile composition of chocolate: Botanical and geographical origins of the cocoa beans,and brand-related formulation and processing

The intrinsic characteristics of chocolate and the complex technological process complicate the assessment of the typical features of this product and the verification of its authenticity. In this study, the influence of the botanical and geographical origin of the cocoa beans, as well as the impact of brand-related processing on the volatile organic compound (VOC) composition of the resulting chocolates was examined. A total of ninety dark chocolates available on the Dutch market were analysed using Proton-Transfer-Reaction-Mass Spectrometry (PTR-MS). The VOC profiles generated by PTR-MS (136 masses per sample) were used as fingerprints and investigated using chemometric tools to elucidate information on production factors of cocoa and subsequent processing, in the finished product. Principal component analysis (PCA) showed some clustering of the chocolates according to the botanical and geographical origins of beans as well as according to the brand. Partial least square discriminant analysis (PLS-DA) further discriminated the samples according to the three classes (botanical origin, geographical origin, brand) and the models with the best classification results were used to investigate the relevant masses for each class. PCA clustering and PLS-DA classification highlighted that chocolate profiles are strongly affected by the processing applied by the different brands. However, reflection of the botanical and geographical origins of the beans was also mirrored in the VOC composition of the chocolates. PTR-Time of Flight-MS (PTR-ToF-MS) was used to tentatively identify the VOCs of the chocolates. These measurements allowed the identification of 36 spectrometric peaks which relate to the main classes of chocolate odorant compounds, in particular, aldehydes and pyrazines, products of Maillard reactions. Several compounds already present in unroasted beans were tentatively identified in the chocolates as well, such as, acetic acid, methylpropanoic acid, 2- and 3-methylbutanoic acid, 2-phenylethanol, and tetramethylpyrazine. The results of this study emphasize the impact of the brand-related formulation and processing on VOC profiles of dark chocolates. However, using chemometrics, VOC reflection of the botanical origin and geographical origin of the beans in the chocolates was revealed, which may be useful for a future cocoa/chocolate traceability.     

An investigation on the appropriateness of chocolate to match tea and coffee

The aim of this study was to provide some recommendations for selecting a befitting tea and coffee to match chocolate with different cocoa contents. Three coffee samples (chocolate flavored, vanilla flavored and unflavored coffee), four tea samples (black tea, green tea, vanilla flavored tea and citrus flavored tea) and three chocolates (30%, 70%, and 99% cocoa) were hedonically rated by eighty regular chocolate consumers. The beverages were then paired with each chocolate, and the consumers were asked to indicate the hedonic liking of the resulting pairings, and to indicate whether the chocolate or beverage flavor dominated the pairing flavor. This study showed that liking of chocolate and coffee pairings and chocolate and tea pairings significantly varied (p < 0.001) across samples. Consumers preferred pairings with 30% cocoa and 70% cocoa chocolate to pairings with 99% cocoa chocolate. Overall, coffee is significantly (p < 0.001) preferred to tea as a chocolate partner.Chocolate and beverage pairing liking was biased by the liking of the beverage tasted alone, the liking of chocolate tasted alone, beverage type, chocolate type and the level of flavor match between chocolate and tea or coffee in a given pairing. When chocolate and beverage flavor balanced out in a given pairing, chocolate and coffee/tea pairings were significantly preferred by the consumers. A significant decrease in acceptance was observed when beverage or chocolate flavor dominated the flavor of the pairing, much more so when the chocolate flavor dominated the pairing flavor. However consumers don't enjoy any preferred chocolate with any preferred tea or coffee because some flavors match better than do others. Indeed, consumers formulate their hedonic responses taking into consideration what flavors go well together more than they rely exclusively on their hedonic judgments of the chocolates, the teas, and the coffees tasted alone.     

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.     

Relationship between bioactive compounds and sensory properties of dark chocolate produced from Brazilian hybrid cocoa

This work evaluated the influence of bioactive compounds on the sensory profile and acceptability of dark chocolate produced from Brazilian hybrid cocoa. The results showed that higher contents of catechin, epicatechin, caffeine, total phenolic compounds and flavonoids contributed to higher intensity of bitterness, cocoa flavour, acid taste, and astringency, and negatively affected the acceptance of chocolate samples from the TSH1188, PH16, and CEPEC2002 varieties. Other varieties SR162 and BN34 showed lower contents of caffeine and phenolic compounds, and higher concentration of theobromine, revealed notes of sweet/caramel and fruity flavour, presented a higher acceptance. This research showed the great potential of the ‘Catongo’ (SR162) and BN34 hybrids from southern Bahia (Brazil) for the production of fine cocoa. The chemical and sensory evaluations may be a strategic tool to help cocoa producers in deciding which genetic varieties should be marketed as fine cocoa, adding value to the product and highlighting promising cocoa varieties.     

Factors influencing quality variation in cocoa (Theobroma cacao) bean flavour profile — A review

This review examined the factors that influence flavour volatiles of cocoa beans and the volume of work that needs to be done on these factors and their impact on the flavour volatiles of commercial cocoa beans. Cocoa bean flavour is one of the most important quality attributes as flavour is central to acceptability of cocoa beans and cocoa products such as chocolate. The complex composition of cocoa bean flavour depends on bean genotype, postharvest treatments such as pulp pre-conditioning, fermentation and drying, industrial processes such as roasting as well as the type of soil and age of cocoa tree. The bean genotype determines the chemical composition of the bean, specifically the contents of bean storage proteins, polysaccharides, and polyphenols. This determines the quantities and type of precursors formed during fermentation and drying processes leading to flavour formation, hence, influencing both flavour type and intensity. Cocoa bean fermentation and drying result in the breakdown of the storage proteins by endogenous proteases into amino acids and short chain oligopeptides while the polysaccharides are also degraded by invertase to glucose and fructose. The amino acids, oligopeptides, glucose and fructose react with each other during the roasting process to produce the typical cocoa flavour volatiles. Polyphenols are also oxidized by polyphenol oxidase during fermentation and drying which reduce the astringency and bitterness of the beans, thus, enhancing the flavour of cocoa beans. However, the extent to which other factors such as age of the cocoa tree and soil chemical compositions influence the formation of flavour precursors and their relationships with final flavour quality remains unclear. With increasing demand for sustainable production of high quality cocoa beans, greater understanding of factors contributing to the variations in flavour character would have significant commercial implications.     

Comparative study of cytotoxic and cytoprotective activities of cocoa products affected by their cocoa solids content and bioactive composition

Polyphenolic profile and antioxidant properties of water extracts of milk, semisweet and dark chocolates, as well as cocoa liquor, were determined and examined for potential biological activity. Non-fat cocoa solids (NFCS), phenolic compounds content and the antioxidant capacity of cocoa product extracts were determined using UV/Vis spectrophotometric methods and HPLC analysis. The increase in NFCS was consistent with the increase in polyphenol content and antioxidant properties. Methylxanthines, theobromine and caffeine constituted the most abundant bioactive compounds, followed by flavan-3-ols epicatechin and procyanidin B2. Cytotoxic and antioxidative/prooxidative effects of cocoa product extracts were determined on human laryngeal carcinoma cell line (HEp2). Cocoa liquor containing the highest NFCS exhibited the lowest HEp2 cell viability, while milk chocolate characterized by the lowest NFCS exhibited no cytotoxic effect. Experiments revealed a strong relationship between the type of product/concentration/time of exposure and antioxidant/prooxidant character of cocoa products. Lower concentrations of semisweet, dark chocolate and cocoa liquor induced an increase in ROS formation, while the higher concentrations resulted in a decrease in ROS formation when compared with control (growth medium). Principal component analysis of the obtained results revealed specific grouping of samples (milk chocolate and cocoa liquor), while the observed dispersions indicated that the outcome of cytotoxic and cytoprotective activities of cocoa products are greatly affected by their concentration.     

Effect of cocoa butter replacement with a β‐glucan‐rich hydrocolloid (C‐trim30) on the rheological and tribological properties of chocolates

BACKGROUND: The food industry has been facing the challenge of developing low‐fat and low‐calorie food products due to rising health awareness of consumers. To meet this consumer demand, an oat β‐glucan‐rich hydrocolloid (C‐trim30) was evaluated as a cocoa butter substitute in chocolates. The effects of C‐trim30 on the rheological, tribological, and textural properties of chocolates were investigated. RESULTS: The viscosity of molten chocolates increased with increasing levels of C‐trim30. Flow behaviors analyzed using the Casson model showed that the Casson viscosity and yield stress increased with increasing concentration of C‐trim30 in the chocolate. Tribological tests on a ball‐on‐flat tribometer showed a reduction in boundary coefficients of friction, with increasing C‐trim30. In addition, hardness of chocolates showed that replacement of cocoa butter with C‐trim30 produced chocolates with softer texture. CONCLUSIONS: The cocoa butter replacement with C‐trim30 up to 10% produced soft chocolates with improved boundary lubrication properties. Also, the chocolate prepared by replacing the cocoa butter with C‐trim30 resulted in a product with a lower caloric value and increased health benefits from the oat β‐glucan. Copyright © 2008 Society of Chemical Industry     

Development and evaluation of a laboratory scale conch for chocolate production

In this study a laboratory scale conch was developed with the purpose of testing new formulations using small amounts of chocolate mass. The equipment was built with working parts of others machines and the chocolate manufactured with the conch was evaluated in relation to the viscosity, moisture, acidity and polyphenol concentration. The resulting chocolate was tempered and then evaluated by a sensory panel. The results were always compared with an industrial conching process. The material used in the assays was dark chocolate (40% cocoa). Data were submitted to variance analysis ( anova ) and when there was significant difference among the averages, the Tukey's test was applied. It was verified that the reduction of moisture and viscosity of the mass in the laboratory scale was similar to industrial scale. The parameters acidity and polyphenols showed no significant alterations when comparing both process scales. However, in the sensory analysis a flavour difference between the processing scales was perceptible.     

Effect of different conching processes on procyanidin content and antioxidant properties of chocolate

The effect of two conching processes, namely Long Time Conching (LTC) and Short Time Conching (STC), on the content of bioactive compounds and on their activity in chocolate was investigated. The dark chocolates so produced were extracted with both organic solvent and water to investigate the content and different contribution of procyanidins, water-soluble phenolic and melanoidin fractions to the overall antioxidant activity. The procyanidin content and pattern were deeply affected by the different processing conditions: after conching the STC-samples presented a higher amount of monomers compared to the LTC-ones which, in turn, resulted more polymerized as confirmed by the presence of P10 polymers.Both STC- and LTC-products presented comparable phenolic content and FRAP values but products collected at the different conching steps, and in particular during LTC, showed a significant improvement of the radical scavenging properties (TEAC_PROC). The aqueous extract showed a lower antioxidant activity compared to TEAC_PROC. Based on the analysis of the melanoidin fraction, no further development of Maillard reaction occurred as a consequence of conching.     

Application of the fast sensory method ‘Rate‐All‐That‐Apply’ in chocolate Quality Control compared with DHS‐GC‐MS

This paper studied the fast sensory Rate‐All‐That‐Apply (RATA) method as a contributor to existing quality control (QC) in chocolate production by comparing it with the outcome of dynamic headspace sampling combined with gas chromatography–mass spectrometry (DHS‐GC‐MS). Seven different chocolates were evaluated by a semi‐trained panel using RATA. RATA showed potential as a sensory evaluation tool which could be part of QC programmes in chocolate production as RATA was efficient to perform and captured important sensory deviations, herein addition of excess lecithin and prolonged roasting. However, product deviations caused by long conching were only detected by DHS‐GC‐MS. A more extreme conching process must occur before it can be perceived by humans. RATA and DHS‐GC‐MS should be used as complementary methods in detecting future important issues in chocolate production. DHS‐GC‐MS detects product deviation from chemical perspectives while sensory evaluation gives information on quality parameters from a perceivable perspective influencing consumer satisfaction.     

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.     

State‐of‐the‐Art Chocolate Manufacture: A Review

The aroma, taste, shine, snap, smoothness, “melt‐in‐your‐mouth” sensation, and texture are all qualities that define chocolate, and all depend on how the cocoa and the chocolate itself are processed. Postharvest handling of the cocoa (fermentation, drying, cleaning, storage, and transport) and its transformation into chocolate (roasting, grinding, conching, tempering, molding, and the addition of core and other ingredients), as well as the packaging, storage, transport, and refrigeration of the finished product all have an important influence on the characteristics of chocolate. The aim of this review was to identify and study the key factors, including microbiological aspects that affect the quality of chocolate, from harvesting the beans right up to the manufacture of the finished products.     

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.