## 3 Results and Discussion
Overall, our results highlighted that e-nose responses were in line with HS-SPME/GC-MS analysis. In addition, e-nose sensors were able to discriminate \"Candonga\" strawberries at the two different ripening stages by differently reacting to specific VOCs from the different fruit samples. ATR-FTIR Discrimination of the Ripening Stage of \"Candonga\" Strawberries and Correlation Analysis with Chemical Data  
Spectral sub-ranges identifying the main strawberry constituents could be detected within the exemplary ATR-FTIR full range spectra (4000-600 cm\({}^{-1}\)) of half-red and red samples (Figure 3A). The broad band centred at 3295 cm\({}^{-1}\) and those at 2928 and 2891 cm\({}^{-1}\) corresponded to the \(\
u\)OH and \(\
u\)CH vibrational modes, respectively. The band at 1717 cm\({}^{-1}\), which is diagnostic of the \(\
u\)C=O vibrational mode of esters or organic acids, revealed the methyl galacturonates of strawberry lectins. The bands at around 1400 cm\({}^{-1}\) arose from the \(\delta\)CH\({}_{2}\) vibrational modes [11]. A magnified view of the spectral region in the fingerprint section (1200 and 800 cm\({}^{-1}\)) containing the specific bands of sugars is shown in Figure 3B. The main vibrational modes in this region include the \(\delta\)C-O-C of the glycosidic linkage, \(\delta\)COH, and \(\
u\)C-C. Clearly, this region is characterized by overlapping bands resulting from the contribution of all the different carbohydrates [11]. The various intensity of the bands, which emerges with stronger evidence from the second derivative of spectra in the 1200-800 cm\({}^{-1}\) range (Figure 3C), reflected the dynamic concentration changes of the various sugars during strawberry ripening. Six different samples of \"Candonga\" strawberries were obtained pooling the collected fruits for each harvest time and the two different ripening stages, gaining a total of three samples for the half-red and three samples for the red fruit. Five technical replicates were performed for each sample obtaining a data set composed of 30 observations and 3401 variables (wavenumber). The PCA model obtained after standard normal variate (SNV) transformation and by mean centring the data showed two principal components with R\({}^{2}\) = 0.947 and Q\({}^{2}\) = 0.941. The score scatter plot of the model is reported in Figure 4A. PCA1, explaining the 79.8% of the total variance, discriminates the samples belonging to the half-red group from those of the red group. As a result, the loading of the first component can be investigated to discover the IR spectral regions capable to distinguish the two groups. Specifically, Figure 4B allows us to observe that the average spectrum is coloured according to the loading value. Moreover, the broad band centred at 3295 cm\({}^{-1}\), the band at 1717 cm\({}^{-1}\) and the band at 1026 cm\({}^{-1}\) were the most related to ripening. The compounds responsible for the signals of the first band decrease their concentration during fruit ripening, while the others increase their concentration along with strawberry maturation. The broad band centred at 3295 cm\({}^{-1}\) corresponds to the \(\
u\)OH vibrational mode of organic acids, while the band 1717 cm\({}^{-1}\) can be ascribed to the \(\
u\)C=O vibrational mode of esters or organic acids. Moreover, the 1200 to 900 cm\({}^{-1}\) spectral range, which includes the band at 1026 cm\({}^{-1}\), is known as the \"fingerprint region\" of sugars [11]. The main vibrational modes absorbing in this region correspond to the \(\delta\)C-O-C of the glycosidic linkage, the \(\delta\)COH, and the \(\
u\)C-C of sugars and organic acids, both affected by the ripening stage of strawberries. Indeed, during fruit ripening the concentration of organic acids tends to drop, while that of sugars (sucrose, glucose and fructose) is likely to increase [28]. Figure 3: (Panel **(A)**): Typical ATR-FTIR spectrum in the 4000–600 cm\({}^{-1}\) range of freeze-dried red (red line) and half-red (green line) strawberries.