The Evaluation of Dark Chocolate-Elicited Emotions and Their Relation with Physico Chemical Attributes of Chocolate

The aim of this study was to evaluate the effect of different origin (Venezuela, Ghana, Peru) dark chocolates on emotions induced for consumers, and to analyse the relationships among overall acceptability (OA), emotions, and physicochemical attributes of the chocolate (fatty acids (FAs) and volatile compounds (VC)). Chocolate-elicited emotions were measured with FaceReader 8 software, scaling 10 emotion patterns (neutral, happy, sad, angry, surprised, scared, disgusted, contempt, valence, arousal). The OA was carried out by using a 10-point hedonic scale, ranging from 1 (extremely dislike) to 10 (extremely like). The obtained results showed that, among all chocolate-elicited emotions, the intensity of “happy” was the highest. In most cases, the influence of the different origin chocolate on the emotions induced for consumers was significant (except on emotions “neutral”, “scared”, and “disgusted”). Significant differences between the tested chocolates OA were not found. The origin of chocolate had a significant effect on most of the identified VC and the content of the main FAs (methyl palmitate, methyl stearate, cis,trans-9- oleic acid methyl ester, and methyl linoleate). Significant correlations between chocolate-elicited emotions and separate FAs and VC were found. Finally, this study showed that the origin of dark chocolate significantly influenced most of chocolate-elicited emotions and physicochemical attributes of chocolate, while separate FAs or VC can be used as chocolate quality indicators related to the chocolate OA, as well as chocolate-elicited emotions.


Introduction
Consumers' satisfaction with a food product is a very important characteristic that can lead to the product's popularity, or in contrast, unpopularity, and stimulate consumers to return or, in contrast, never choose this product again in the future [1]. The sensory properties of chocolate make it one of the favourite treats worldwide. Recently, the consumption of dark chocolates increased, because of its health benefits described in literature [2][3][4]. It was reported that a high content of polyphenols in cocoa possesses desirable biological effects: antiatherosclerotic, anti-inflammatory, and regulation of the blood pressure and immune-response [5]. However, studies about the chocolate health benefits are controversial. It is important to point out that most chocolate is high in fat and free sugars, so should be consumed less often and in small amounts [6]. As well as dark chocolate is high in calories and can contribute to weight gain if eaten in excess [7]. It is difficult to be sure about the potential health effects and eating modest quantities may offer the greatest health benefits [8]. High-quality evidence for significant health benefits of dark chocolate has not been shown [9,10]. among overall acceptability, emotions, and physicochemical attributes of the chocolate: fatty acids and volatile compounds.

Samples of the Dark Chocolate Preparation
In total, 4 samples of the dark chocolate, by using different cocoa mass (country of origin Venezuela (KÖLLA Valencia S.L., Valencia, Spain)-samples group S1, country of origin Ghana (KÖLLA Valencia S.L., Valencia, Spain)-samples group S2, country of origin Peru: ecological-samples group S3 (Natra cocoa S.L., Valencia, Spain) and nonecological-samples group S4 (KÖLLA Valencia S.L., Valencia, Spain)) were prepared at laboratory scale. Dry matter of cacao mass was 70%. Recipe of chocolate consist of 70% of cacao mass, 29.6% saccharose (obtained from "Nordic Sugar", Kedainiai, Lithuania), 0.4% sunflower lecithin (obtained from "Naturz Organics", Helmond, The Nederlands). The technological scheme of chocolate preparation is shown in Figure 1. Melting of the cacao mass was performed at 38-40 • C. Then, saccharose and lecithin were added, and a mass was homogenised in a ball mill (CAO B5: laboratory ball mill refiner, "Caotech b.v. Grinding Technology", Wormerveer, The Nederlands). Chocolate mass was tempered, filled to the silicon molds, and cooled at 4 • C. Before the experiment, chocolate mass was kept in the dark place at 21 ± 2 • C. The aim of this study was to evaluate the effect of different origin (Venezuela, Ghana, Peru) dark chocolates on emotions induced for consumers, and to analyse the relationships among overall acceptability, emotions, and physicochemical attributes of the chocolate: fatty acids and volatile compounds.

Samples of the Dark Chocolate Preparation
In total, 4 samples of the dark chocolate, by using different cocoa mass (country of origin Venezuela (KÖLLA Valencia S.L., Valencia, Spain)-samples group S1, country of origin Ghana (KÖLLA Valencia S.L., Valencia, Spain)-samples group S2, country of origin Peru: ecological-samples group S3 (Natra cocoa S.L., Valencia, Spain) and nonecological-samples group S4 (KÖLLA Valencia S.L., Valencia, Spain)) were prepared at laboratory scale. Dry matter of cacao mass was 70%. Recipe of chocolate consist of 70% of cacao mass, 29.6% saccharose (obtained from "Nordic Sugar", Kedainiai, Lithuania), 0.4% sunflower lecithin (obtained from "Naturz Organics", Helmond, The Nederlands). The technological scheme of chocolate preparation is shown in Figure 1. Melting of the cacao mass was performed at 38-40 °C. Then, saccharose and lecithin were added, and a mass was homogenised in a ball mill (CAO B5: laboratory ball mill refiner, "Caotech b.v. Grinding Technology", Wormerveer, The Nederlands). Chocolate mass was tempered, filled to the silicon molds, and cooled at 4 °C. Before the experiment, chocolate mass was kept in the dark place at 21 ± 2 °C.

Evaluation of the Dark Chocolate Overall Acceptability and Emotions Induced for Consumers
The analysis was performed at the Lithuanian University of Health Sciences Sensory laboratory, which is equipped with sensory booths. Dark chocolate samples were evaluated by 30 panelists (age from 25 till 50 years, 15 women and 15 men). Mammasse and Schlich [32] reported that the suitable number of panelists could range from 20 to 150. depending on the level of complexity among test samples. Therefore, it should be noted that a small number of panelists might be a limitation of this study. Chocolate samples were prepared as pieces and presented in four separate serving plates with different codes. The panelist tasted the presented samples one by one in front of a webcam (Microsoft Corporation, Redmond, WA, USA). The tasting procedure was recorded. After tasting each sample, the panelist raised their hand and visualized the taste experience with a facial expression. The time for that was not limited. After that, the panelist was asked to evaluate the overall acceptability of sample using a 10-point hedonic scale, ranging from 1 (extremely dislike) to 10 (extremely like). Between samples, the panelists were asked to rinse the mouth with warm (40 ± 2 °C) water. To evaluate the chocolate-elicited emotions

Evaluation of the Dark Chocolate Overall Acceptability and Emotions Induced for Consumers
The analysis was performed at the Lithuanian University of Health Sciences Sensory laboratory, which is equipped with sensory booths. Dark chocolate samples were evaluated by 30 panelists (age from 25 till 50 years, 15 women and 15 men). Mammasse and Schlich [32] reported that the suitable number of panelists could range from 20 to 150. depending on the level of complexity among test samples. Therefore, it should be noted that a small number of panelists might be a limitation of this study. Chocolate samples were prepared as pieces and presented in four separate serving plates with different codes. The panelist tasted the presented samples one by one in front of a webcam (Microsoft Corporation, Redmond, WA, USA). The tasting procedure was recorded. After tasting each sample, the panelist raised their hand and visualized the taste experience with a facial expression. The time for that was not limited. After that, the panelist was asked to evaluate the overall acceptability of sample using a 10-point hedonic scale, ranging from 1 (extremely dislike) to 10 (extremely like). Between samples, the panelists were asked to rinse the mouth with warm (40 ± 2 • C) water. To evaluate the chocolate-elicited emotions (neutral, happy, surprised, sad, scared, angry, contempt, arousal, disgusted, and valence), the recorded videos were analysed with FaceReader 8 software (Noldus Information Technology, Wageningen, The Netherlands). Only part of video when panelist raise his hand was used for the analysis of chocolate-elicited emotions. The intensity of each emotion was expressed in a scale from 0 (no emotion) to 1 (highest intensity of emotion). The experimental scheme used to evaluate the emotions elicited by different chocolate samples is given in Figure 2. (neutral, happy, surprised, sad, scared, angry, contempt, arousal, disgusted, and valence), the recorded videos were analysed with FaceReader 8 software (Noldus Information Technology, Wageningen, The Netherlands). Only part of video when panelist raise his hand was used for the analysis of chocolate-elicited emotions. The intensity of each emotion was expressed in a scale from 0 (no emotion) to 1 (highest intensity of emotion). The experimental scheme used to evaluate the emotions elicited by different chocolate samples is given in Figure 2.

Fatty Acid Profile Analysis
The extraction of lipids for fatty acids (FA) analysis was done with chloroform/methanol (2:1 v/v) and fatty acid methyl esters (FAME) were prepared according to Pérez-Palacios et al. [33]. FA composition of the dark chocolate was identified using a gas chromatograph GC -2010 Plus (Shimadzu corp.) equipped with Mass Spectrometer GCMS-QP2010 (Shimadzu corp.). Separation was carried out on a Stabilwax-MS column (30 m length, 0.25 mmID, and 0.25 μm df) (Restek). Oven temperature programming started at 50 °C, it was raised 8 °C/min to 220 °C, held for 1 min at 220 °C, increased again at 20 °C/min to 240 °C, and held for the last 10 min. Injector temperature was 240 °C, interface −240 °C, and ion source 240 °C. The carrier gas was helium at a flow rate of 0.91 mL/min. The Individual FAME peaks were identified by comparing their retention times with those of standards (Merck & Co., Inc., Kenilworth, NJ, USA).

Analysis of Volatile Compounds by GC-MS Method
The volatile compounds (VC) in chocolate samples were analysed by gas chromatography-mass spectrometry (GC-MS) as described in Bartkiene et al. [34] with some modifications. Solid phase microextraction (SPME) device with Stableflex (TM) fiber coated with 85 μm PDMS-Carboxen™ layer (Supelco, Bellefonte, PA, USA) was used to prepare samples. For headspace extraction, 2 g of sample in the 20 mL extraction vial sealed with polytetrafluoroethylene septa was thermostated at 60 °C for 15 min, exposing the fiber in the headspace. The fiber was exposed to the headspace of the vial for 10 min. The desorption time was 2 min. Prepared samples were analysed with a GCMS-QP2010 (Shimadzu, Kyoto, Japan) gas chromatograph and a mass spectrometer. The following method conditions were used for analysis: injector temperature 250 °C, ion source temperature 220 °C, interface temperature 280 °C. Sample injection was carried out for 2 min on order to ensure full desorption of volatiles from the SPME fiber. The temperature gradient was programmed from start at 35 °C (5 min hold) to 200 °C (10 °C/min) up to 280 °C (25 °C/min) (5 min hold). The VCs were identified according to the mass spectra libraries (NIST11, NIST11S, FFNSC2).

Fatty Acid Profile Analysis
The extraction of lipids for fatty acids (FA) analysis was done with chloroform/meth anol (2:1 v/v) and fatty acid methyl esters (FAME) were prepared according to Pérez-Palacios et al. [33]. FA composition of the dark chocolate was identified using a gas chromatograph GC -2010 Plus (Shimadzu corp.) equipped with Mass Spectrometer GCMS-QP2010 (Shimadzu corp.). Separation was carried out on a Stabilwax-MS column (30 m length, 0.25 mmID, and 0.25 µm df ) (Restek). Oven temperature programming started at 50 • C, it was raised 8 • C/min to 220 • C, held for 1 min at 220 • C, increased again at 20 • C/min to 240 • C, and held for the last 10 min. Injector temperature was 240 • C, interface −240 • C, and ion source 240 • C. The carrier gas was helium at a flow rate of 0.91 mL/min. The Individual FAME peaks were identified by comparing their retention times with those of standards (Merck & Co., Inc., Kenilworth, NJ, USA).

Analysis of Volatile Compounds by GC-MS Method
The volatile compounds (VC) in chocolate samples were analysed by gas chromatogra phy-mass spectrometry (GC-MS) as described in Bartkiene et al. [34] with some modifications. Solid phase microextraction (SPME) device with Stableflex (TM) fiber coated with 85 µm PDMS-Carboxen™ layer (Supelco, Bellefonte, PA, USA) was used to prepare samples. For headspace extraction, 2 g of sample in the 20 mL extraction vial sealed with polytetrafluoroethylene septa was thermostated at 60 • C for 15 min, exposing the fiber in the headspace. The fiber was exposed to the headspace of the vial for 10 min. The desorption time was 2 min. Prepared samples were analysed with a GCMS-QP2010 (Shimadzu, Kyoto, Japan) gas chromatograph and a mass spectrometer. The following method conditions were used for analysis: injector temperature 250 • C, ion source temperature 220 • C, interface temperature 280 • C. Sample injection was carried out for 2 min on order to ensure full desorption of volatiles from the SPME fiber. The temperature gradient was programmed from start at 35 • C (5 min hold) to 200 • C (10 • C/min) up to 280 • C (25 • C/min) (5 min hold). The VCs were identified according to the mass spectra libraries (NIST11, NIST11S, FFNSC2).

Statistical Analysis
The results were expressed as the mean ± standard deviation (SD). The data were analyzed using the statistical package SPSS for Windows (v15.0, SPSS Inc., Chicago, IL, USA). The normal distribution of data was checked using Descriptive Statistics tests. In order to evaluate the influence of the different type of dark chocolate on induced emotions, FA profile, and aromatic compounds, data were analyzed by the one-way ANOVA and Tukey's honestly significant difference (HSD) procedure, as post-hoc tests. A linear Pearson's correlation was used to quantify the strength of the relationship between the variables (0.00-0.19, very weak; 0.20-0.39, weak; 0.40-0.59, moderate; 0.60-0.79, strong; 0.80-1.0, very strong) [35]. The results were recognized as statistically significant at p ≤ 0.05.

Overall Acceptability and Emotions Induced by the Dark Chocolate for Consumers
Results of the overall acceptability test and emotions induced by the dark chocolate for consumers are shown in Table 1. Significant differences of the tested chocolate samples overall acceptability were not found, and, on average, the overall acceptability of the samples was 8.2 points. The dark chocolate elicited the highest intensity of happiness (on average, 0.746. In most of the cases, the influence of the different chocolate mass on the emotions response for consumers was significant (p ≤ 0.05) (except on emotions "neutral", "scared" and "disgusted"). Consumers felt slightly higher intensity of "happy" when consuming chocolate sample S2, following by samples S1, S4, and S3. The highest emotion "sad" expression was fixed by testing S4 sample (0.015). The lowest "angry" emotion was expressed by testing S2 sample, however, by testing S1, S3, and S4 groups, emotion "angry" was fixed by 7, 12, and 6 times, respectively, more intensive. Consumers felt the lowest intensity of emotion "surprised" by testing S2 samples (0.004), also, S2 samples induced the lowest expression of the emotion "contempt". Samples S3 induced, also, low expression of "contempt", in comparing with S1 and S4 samples. Negative moderate correlation between the overall acceptability of the dark chocolate and emotion "contempt" was established (r = 0.58) (Supplementary Table S1). Various sensory science methods have been developed to assess the emotions induced by food for consumers [36]. Most studies use explicit response measures by questionnaires that comprise a forced yes/no variant of CATA questions [37]. Food choice is related with a very complex function of preferences for sensory, as well as non-sensory attributes, including expectations and attitudes, price, ethical concerns, food-mood relation, and health claims [38][39][40]. One from the characteristics of chocolate is mood-enhancing properties, however, till now, opinion about which constituents may contribute to the psychopharmacological activities is controversial, and can be related with many compounds: flavanols, methylxanthines, salsolinol etc. [41]. Also, consumers tend to consume food as a form of self-expression, for lifestyle, image positioning etc. [42]. For this reason, the places where chocolate is sold also become very important and related with consumers' choice [40]. However, in this case, only the emotion "contempt" correlated with overall acceptability, and this indicates that the facial expression analysis measures are not sensitive Foods 2021, 10, 642 6 of 12 enough to distinguish between these emotional responses. Finally, further research is needed, in which more factors, related with the chocolate choice should be included. This is because such factors as craving [43,44] or feeling depressed [45] can lead to changes of the chocolate choice.

Fatty Acid Profile of the Dark Chocolate Samples
Fatty acid profile of the dark chocolate samples is shown in Table 2. The main FAs in all the tested chocolate samples were methyl palmitate (C16:0), methyl stearate (C18:0), cis,trans-9oleic acid methyl ester (C18:0 cis,trans), and methyl linoleate (C18:2), and the different cacao mass, used for chocolate preparation, was significant factor on these FAs content (p ≤ 0.05). In comparing saturated (SFAs), monounsaturated (MUFAs), polyunsaturated (PUFAs), omega-3, 6, and 9 FAs in different chocolate samples, the highest content of SFAs in the S4 chocolate samples was found. The highest MUFAs, PUFAs, and omega-9 in S2 chocolate was established. On average, by 8.6, 1.9, and 5.0 times that in S1, S2, and S4 samples, respectively, the content of omega-3 in S3 samples was found, and the highest content of omega-6 in S1 samples was established.

Volatile Compounds Profile of the Dark Chocolate
The volatile compounds (VC) profile (volatile acids, alcohols, aldehydes, esters, ketones, pyrazines, furans, among others) of the dark-chocolate samples was evaluated in order to identify possible key aroma markers associated with the different chocolate samples, prepared from the different cacao mass, as well as to evaluate which VC has the strongest correlations with overall acceptability and emotions induced for consumers (Supplementary Table S3). It was reported that several VC of the chocolate aroma are formed as a result of the technological processes [16,50]. However, the short-chain carboxylic acid, acetic acid, was the main VC identified in all the analysed chocolate samples, with the highest percentage in S4, and the lowest in S2 samples (78.23 and 67.90%, respectively). Acetic acid is the most intensive cacao VC profile compound, characterized by a vinegar-like odor [51]. The percentage of VC was varied in the different chocolate samples, and different cacao mass was a significant factor most of the identified VC (p ≤ 0.05). Out of the 119 VC identified, 29 were found in all, out of the four analysed, chocolate samples. Sample S3 showed the highest percentage of 2,3-butanediol, which odor is described as fruity, creamy, and buttery, however, 2,3-butanediol correlation with emotion "happy" was negative moderate (r = −0.636). As well as a negative correlations between the 2,3butanediol and emotions "sad", "angry", "surprised", "scared", and "valence" were found (r = −0.721, r = −0.598, r = −0.859, r = −0.695, and r = −0.901, respectively). Also, 2,3butanediol, [R-(R*, R*)] was found in all the tested chocolate samples, as well as a very strong positive correlation between this VC and "sad" emotion was established (r = 0.884).
In comparing the typical VC for separate chocolate samples in S1, S2, S3, and S4, out of all identified VC, there were 16, 15, 9, and 16, respectively, VC were typical just for particular sample. In S1 samples, despite a common VC identified in other samples, the main typical VC were 2,3-butanediol, [S-(R*, R*)], which odor is described as fruity and rum-like (2.60%); butanoic acid, 3-methyl-, whose odor is described as rancid and cheesy (0.41%); 2-heptanol (0.48%), which is associated with mushroom odor; sulfurous acid, isobuthyl 2-pentyl ester (0.62%), whose odor is described as orange juicy, impacting, musty green, unripe, fruity, reminiscent of banana and vegetative nuances with a slight nutty note; nonanal (0.40%), which odor is described as waxy, aldehydic, citrus, with a fresh slightly green lemon peel like nuance, and a cucumber fattiness, and other VC in lower percentages. Further, 2,3-Butanediol is eligible VC in high-quality cocoa products because it has a good stability during the production of chocolate [20,50].
Chocolate taste and aroma is directly connected to the contents of volatile aroma compounds [52]. Such VC as alcohols, sulfides, and ketones may have a significant impact on chocolate taste and odor [53]. It has been reported that the presence of acetic acid, 2-methylpropanoic acid, 3-methylbutanoic acid and hexanoic acid was observed in dark chocolate [54]. Flowery and candy notes of dark chocolate are induced by the high content of alcohol, such as 2-phenylethyl alcohol, while 3-methyl-butanal and phenylacetaldehydes are the main compounds associated with malty and honey-like odor [1]. In general, there is a little information in literature about the relation between the acceptance, or even emotional response, of dark chocolate by consumers and the factors affecting it. It has been reported that the most liked chocolate by panelists was related with sweet and bitter taste due to the by the presence of flavor compounds, such as 2,3-butanediol and 2-methyl-1butanol. However, chocolate with a higher content of acids was evaluated by the panelists as the less liked sample [55].

Conclusions
Nowadays, food-elicited emotions become more and more important element in the assessment of food products acceptability and popularity in market. Chocolate is one of the favourite products worldwide and its sensory properties are highly related with the profile of fatty acids and volatile compounds. Therefore, different FA and VC profiles might lead to different emotional responses in consumers. This study showed that the origin of cacao mass had a significant effect on most of the identified VC and the content of the main FAs (methyl palmitate, methyl stearate, cis,trans-9oleic acid methyl ester and methyl linoleate) in tested chocolates. In most of the cases, the influence of the different origin chocolates on the emotions response for consumers was significant (except on "neutral", "scared", and "disgusted" emotions), although significant differences between different origin chocolates overall acceptability were not found. Also, significant correlations between the emotions induced for consumers by the tested chocolates and separate FAs and VC were found. In general, the intensity of "happy" emotion was the highest compared to other emotions. However, only the emotion "contempt" correlated with overall acceptability, and this indicates that the facial expression analysis measures are not sensitive enough to distinguish between these emotional responses. In this case, further research is needed, whereby more factors related with the chocolate choice and chocolate-induced emotions should be included. Finally, the obtained results of the relation of the sensory/emotional responses with separate chocolate FA and VC profile compounds can provide additional value in food and emotions related studies as well as in the food industry. Furthermore, a prognosis concerning product popularity on the market could be made, and technological steps for chocolate quality improvement can be taken.
Supplementary Materials: The following are available online at https://www.mdpi.com/2304-815 8/10/3/642/s1, Table S1: Pearson correlations between overall acceptability and emotion response of the dark chocolate samples; Table S2: Pearson correlations between overall acceptability and emotions response of the dark chocolate samples with fatty acids; Table S3: Volatile compounds (%) of the dark chocolate identified by HS-SPME GC-MS; Table S4