# Comparison of the Chemical and Sensorial Evaluation of Dark Chocolate Bars
## 3 Results and Discussion
### Statistical Analysis of Chemical Data  
The hierarchical cluster analysis (HCA) dendrogram is reported in Figure 1.  
Two main macro-groups were identified by the HCA; the first one (red group, Figure 1) mainly composed of SM bars, and a larger, more varied one composed of two sub-groups (green and blue, Figure 1). Although no completely sharp distribution was evidenced among the samples, an overall grouping of bars sharing the same commercial origin was visible for SM and HD samples. BIO bars were not clustered very close; this could be due to the high variability induced by the raw starting material and processing method, as well as to their smaller sample size. The score and loading plots of the principal component analysis (PCA) are reported in Figure 2.  
Half of HD bars (HD4, 5, 6, and 8) were plotted in the upper left quadrant (PC1 \(<\) 0, PC2 \(>\) 0) of the PCA score plot (Figure 2, left); this positioning was due to their higher content in tetramethyl pyrazine, whose vector was sharply directed towards the  
Figure 1: Dendrogram of the hierarchical cluster analysis (HCA) performed on the complete headspace compositions of all bars. Legend for the sample names: organic bars (BIO), supermarket bars (SM), and hard discount bars (HD). Figure 2: Score (**left**) and loading (**right**) plots of the principal component analysis (PCA) performed on the complete headspace compositions of all bars. Legend for the sample names: organic bars (BIO), supermarket bars (SM), and hard discount bars (HD). left side of the loadings plot (Figure 2, right). The other 4 HD bars were all distributed in the right quadrants (PC1 \(>\) 0), between the bottom area of the upper quadrant (PC2 \(>\) 0) and the upper area of the bottom quadrant (PC2 \(<\) 0); compared to the other HD bars, their compositions were richer in nonanal, whose vector pointed towards the right quadrant of the loadings plot (Figure 2, right). Samples previously grouped by HCA in the first macro-cluster (samples in red, Figure 1) were all plotted in the right (PC1 \(>\) 0) score plot quadrants, where only a few samples of the other macro-cluster were positioned, in the bottom right quadrant (PC2 \(<\) 0). All other samples from the second HCA macro-cluster were grouped quite close to each other towards the central area of the left quadrants (PC1 \(<\) 0), mainly due to tetramethylpyrazine vector (Figure 2, right). Samples plotted quite distant from all others were BIO1 and SM13 in the upper right quadrant (PC1 and PC2 \(>\) 0), due to their higher relative content in ethyl acetate (Figure 2, right), and SM4 in the bottom right quadrant (PC1 \(>\) 0, PC2 \(<\) 0), whose position was due to the tetradecanal vector (Figure 2, right). The VOCs emission, used as a tool to evidence the overall distribution of samples by statistical means, could not sharply divide samples based on their commercial origin; however, it demonstrated a general ability to group SM and HD bars. The 2 BIO samples, however, were clustered and plotted as two very distant samples; a larger difference in degree in the raw material quality and/or the processing technology might thus be hypothesized for these samples compared to their SM and HD counterparts. However, the size of the BIO group is too small to draw definitive conclusions on the matter. In accordance with the results emerged from the HSs analysis, each bar, no matter its commercial fragment of origin (HD, SM, or BIO), displayed a unique profile, based on all the phases involved in the development of an aroma bouquet as complex as that of chocolate. The overall aroma profiles for all samples were, indeed, composed of the expected main chemical groups (pyrazines and esters). The secondary chemical classes, such as aldehydes, ketones, and alcohols, displayed higher variability among the samples, but without evidencing any pattern that might be attributed to the commercial segment of the product.