## 3 Results and Discussion
### Influence of YE Treatment on the Norisoprenoid Aroma Potential (\(\Delta\)C)  
As accepted, C\({}_{13}\)-norisoprenoid varietal aroma in wine grapes is strictly related to carotenoid degradation during ripening [5; 29]. Therefore, determining the difference of total carotenoids between veraison and harvest points (\(\Delta\)C) together with their decreasing kinetics can be a useful tool for defining the aroma potentiality of grapes for wine making [7]. On the other side, elicitor treatment by foliar application in vineyards has proved to influence the development of aroma compounds in wines [19]; in particular, grapevines treated with benzothiadiazole have been shown to increase the concentrations of some C\({}_{13}\)-norisoprenoids, such as \(\beta\)-damascenone and \(\beta\) -ionnone, while the use of methyl jasmonate did not alter their content [30].  
In our work, a similar change in norisoprenoid aroma potential was shown by control samples of Negro Amaro and Primitivo, with \(\Delta\)C values of 270 \(\mu\)g/kg and 290 \(\mu\)g/kg, respectively (Tables 2 and 3). This finding was in agreement with data from a 3 year-long study conducted on the same cultivars in Apulia [7]. Moreover, the YE treatment significantly affected the aroma potential of the grapes, increasing the \(\Delta\)Cs 2.6 and 4.2-fold in Primitivo (740 \(\mu\)g/kg) and Negro Amaro (1130 \(\mu\)g/kg), respectively (Tables 2 and 3). In the literature, it is well documented that the use of elicitors (i.e., methyl jasmonate, chitosan, yeast extracts) stimulates plant defense mechanisms and consequently activates the enzymes responsible for the biosynthesis of secondary metabolites, such as phenolic compounds [16; 31]. YE caused an accumulation of anthocyanins, stilbenes, and flavonoids in wine grapes without varying their phenological maturation [18; 32; 33]. Since there was no significant difference in maturation indexes between YE and C samples (Tables 2 and 3), the effect of treatment  
Figure 6: Violaxanthin (**a**), (9’Z)-neoxanthin (**b**), and 5,6-epoxy lutein (**c**) contents in yeast extract-treated (YE) and control (C) Negro Amaro and Primitivo wine grapes during ripening.  
on \(\Delta C\) variation could be attributed to the activation of enzymes catalyzing either the biosynthesis of carotenoids (as proved by the highest values being in YE grapes at veraison) or their degradation (as confirmed by the lowest values being in YE grapes at harvest) (Figure 4).  
The knowledge of the carotenoid profile of grapes is linked to the type of norisoprenoid compound which will form in wine. \(\beta\)-ionone is derived from \(\beta\)-carotene oxidation, whereas 3-hydroxy-\(\alpha\)-ionone and 3-oxo-\(\alpha\)-ionol originate by lutein cleavage [11; 12]. The factor score plot (accounting for 82.06% of total variance) from the PCA performed on the variables corresponding to the difference of the identified carotenoid level between veraison and harvest in both YE and C grape samples is shown in Figure 7. This clearly shows that YE-treated grapes of Negro Amaro and Primitivo were different from C samples along PC\({}_{1}\) and PC\({}_{2}\), respectively, and they were more correlated to carotenoid-derivative variables. Furthermore, NYE was mainly characterized by lutein, \(\beta\)-carotene, and violaxanthin derivatives (factor coordinates: \(-\)0.9535, \(-\)0.8657, and \(-\)0.8643, respectively, onto PC\({}_{1}\)), while PYE was principally characterized by a higher concentration of (9'Z)-neoxanthin derivatives (factor coordinate: \(-\)0.8492 onto PC\({}_{2}\)) (Figure 7).