# Black Truffle Aroma Evaluation: SPME-GC-MS vs. Sensory Experts
## 3 Results and Discussion
### Relationships between Sensory and Instrumental Aroma Measurements  
The application of PCA analysis with VOCs and sensory data separated the samples with similar behavior, according to the harvesting time. The trained panel plot explained 76.1% of the variability with the first two components, showing a higher percentage of explained data variability compared with the VOCs PCA (47.1%). This difference can be explained by the amount of data in the VOCs PCA (69 compounds) compared to eight aromatic attributes evaluated in this PCA. A Sankey diagram was used to visualize possible relations between sensory attributes evaluated by the trained panel and aromatic VOCs (Figure 4). Only the VOCs detected by SPME-GC-MS with aromatic notes were represented in the diagram. Truffle sulfur and black olive aromas were due to DMS and DMDS compounds. Several authors agree ([PERSON], 2016), but more molecules have the same aromatic attribute in _T. melanosporum_. For instance, [PERSON] and [PERSON] (2015) ([PERSON], 2016) identified four diopentene derivates in T. _borchi_ as sulfur volatiles that contribute to human-sensed truffle  
Figure 3: Bi-plot from correspondence analysis of evaluated aromatic attributes (colored in red) for 14 truffles samples (colored in blue) evaluated by the trained panel. Samples are labeled with the same identificatory factors as in Table 2. The 95% confidence ellipses colors correspond to the harvesting time: December (red), January (blue), February (green). aromas. [PERSON] et al. (2023) [7] reported up to three non-identified molecules with truffle odor descriptors in _T. melanogaster_ via gas chromatography-olfactometry. Furthermore, [PERSON] et al. (2017) [6] reported a non-identified molecule in black truffle with a truffle aroma using the same technology. Methanethiol has been also reported as a truffle aroma; indeed, its conversion into DMS, DMDS, dimethyl trisulphide, and H\({}_{2}\)S in _T. melanogaster_ and T. _borchii_ has been reported [4; 39]. The fermentation aroma might be due to 1-propanol (alcohol, pungent), 2-methyl-propanal (pungent, malt), butanal-3-methyl (malt), pentanal (malt, pungent), 3-methyl-1-butanol (malt, whiskey), and 2-methyl-1-butanol (wine, onion). All these molecules were previously found in _T. melanogaster_[2; 6; 7] and are related to malt, wine, and whiskey fermentation processes. The attribute leather aroma was linked with 3-methyl-2-butanone and 3-methyl-phenol. Furthermore, 3-ethylphenol, 3-ethyl-5-methylphenol, p-cresol, and 3-propylphenol have been also reported as compounds with leather aromatic notes [2; 6]. The molecules butanal-2-methyl, pentanal, benzaldehyde, 3-octanol, and E-2-octenal were related to nut odors. Also, 2-acetyl tetrahydropyridine and 2-acetyl-1-pyroline compounds were described as almond-like and toasted almond odors, respectively, in _T. melanogaster_ truffles [7]. Figure 4: Sankey diagram of sensory attributes evaluated by the trained panel and aromatic VOCs. Data correspond to the relation established in Table S3. Each correlation was scored as 1 in the diagram. The straw aroma was linked to hexanal and 1-heptanol molecules. The first one has been also described as leafy [6]. Some identified enzymes, that play a key role in fruits, vegetables, and mushrooms were able to release some odorous compounds like green-grassy-smelling aldehydes such as hexanal [40]. This aromatic attribute might be due to a combination of other molecules since hexanal and 1-heptanol have a greener smell. Nevertheless, depending on the molecule concentration, the smell might be different [41]. The butter aroma has been related to molecules such as heptanal, 3-octanone, octanal, caprylic acid, ethyl caprylate, 2,4-nonadien, and nonanoic acid. Also, 2,3-butadonione and 2,3-pentanodione were shown as buttery smell compounds in _T. melanogaster_ and _T. aestivum_ truffles [7; 42]. The typical butter aroma is mainly due to lactic acid bacteria fermentation, and (E)- and (Z)-2-nonenal and (E,E)-2,4-decadienal compounds confer green and oily notes [43].