# Internet of Food (IoF), Tailor-Made Metal Oxide Gas Sensors to Support Tea Supply Chain
## 4 Discussion  
Regarding the GC-MS results from the treated green teas, an average of 100 volatile compounds were found for each sample analyzed, of which only seven in common to all samples (Table 3). As can be seen from the description, all are naturally occurring compounds in various foods and drinks, especially fruit and vegetables, except for cyanoacetic acid which is a precursor of synthetic caffeine. Volatile compounds give the tea floral, fruity, vegetable, spicy, and aromatic notes. On the other hand, regarding the GC-MS results from the black tea samples, seven teas were subjected to GC-MS analysis, with different characteristics. The results obtained showed that there were four VOCs in common to all the samples (Table 4). In general, EBP, SBL, and TBC were present in more than 100 VOCs, but in the others, about 90 have been found. The few compounds common to black teas can be explained by vanilla flavored black tea (TBV), which has fewer compounds in common with the other samples. The four citrus-flavored samples (TBL, EBB, EBL, and SBL) have five compounds in common over the previous four: \(\beta\)-myrcene, D-limonene, Benzaldehyde, \(\alpha\)-terpineol, and Carvone, which are present in citrus fruits both in essential oils and in peels. In TBV, there is a maximum peak in the direction of vanillin, which is the aromatic aldehyde that gives the vanilla aroma, which records an abundance of 8.287 \(\times\) 10\({}^{6}\). In general, even in black teas, as already found in green teas, volatile compounds are present in nature and impart aromas that have floral, vegetable, spicy, fruity, and aromatic notes. Nonetheless, the results obtained throughout the use of the sensor device show a good rate of identification for the teas, since more than the 80% of the explained variance was enclosed between PC1 and PC2, and good clustering capacity can be seen in Figure 2.  
Taking into consideration the response of one of the RGTO sensors for the green teas' analysis, in particular SGP, SGL, and SMG, it is evident, in the graphs of the normalized resistance as a function of time (Figure 2a), how the samples are well separated according to the different aromatization, even if some have similar values. In fact, as can be seen in Figure 2a, the violet and blue values are more similar to each other. It looks even better in bar charts where the line on the bars is the indicated standard deviation of the mean, highlighting its reproducibility (Figure 2b). On Figure 3, the results of the PCA analysis performed on green teas measurements is shown, and it is evident the separation between the green tea samples, in particular SGP, is far from SGL and SGM. This result is important not only because the instrument is able to  
Figure 5: PCA analysis representing the results obtained from the comparison between black tea. recognize the aromatization tea from the pure one, separating the 2 different ones which actually slightly overlap. The result obtained is very satisfactory, because considering the two main components, the total explained variance enclosed in the graph reaches 87.82%. On the other hand, EBP, EBL, EBB, SBL, and TBC samples were taken into consideration for the analysis of the sensors' response. Figure 4a,b clearly shows the different responses of a SnO2 RGTO sensor to the various black tea samples. This aspect is even more evident in the bar graphs (Figure 4b). It can be observed that the samples of EBP, EBB, and EBL, all of the same brand, have a variation that is very similar to each other, while the other two (SBL and TBC) have a very different variation from the first three and are also quite different between themselves. In this case, two samples of black tea aromatized with lemon were taken into consideration but of different brands, and as can be seen in the figures, the two are very different from each other, as the variation associated with SLB tea is much greater than that of ELB tea.