## 3 Results and Discussion
### Bound Volatile Aroma Compounds in Fresh Grapes and Dried Grapes
In contrast, in chamber-dried grapes, the concentration of \(\beta\)-damascenone decreased. \(\beta\)-damascenone is a norisoprenoid derived from the degradation of carotenoids. An increase in \(\beta\)-damascenone concentration is expected, as water loss / drying is a stress factor that triggers many physiological changes in grapes (expression of genes that regulate carotenoid biodegradation and aroma compound biosynthesis as reported by [PERSON] et al. [38] and [PERSON] et al. [39]). These processes can be triggered even in the freezing process in vine at \(-8\)\({}^{\circ}\)C, in ice grapes, but the loss of mass (concentration) alone is certainly not a decisive factor in explaining the increase in \(\beta\)-damascenone in grapes during drying [39]. In our study, we found that the drying temperature (50 \({}^{\circ}\)C), despite the concentration effect, negatively impacts and reduces the \(\beta\)-damascenone concentration in the grapes, perhaps due to the inactivation of key enzymes involved in its precursor biosynthesis. Different precursors of \(\beta\)-damascenone have been identified in grapes [40] either as glycoconjugates or free norisoprenoids [41]. Acid hydrolysis of glycosidic precursors and subsequent possible rearrangements are likely to be the reason for the increase observed for \(\beta\)-damascenone. \(\beta\)-damascenone is the key aroma compound of sun-dried grapes and the wines made from them [12]. This compound played an important role in the flavor of 'Marasitna' grapes, in both types of dried grapes and fresh too. It has quite a low aroma threshold, close to the ng/L, and the aroma of prunes or overripe plums. In order to determine the influence of the grape drying technique on the differentiation of free and bound volatile components from fresh grapes, we applied principal component analysis (PCA). The PCA showed that 78.96% of the total variance was explained by the first two components (D1 and D2, Figure 1A), whereby the first principal component (D1) explained 46.35% and the second one (D2) 32.61%. The investigated grape samples were separated into three clusters based on the freshness/drying (Figure 1A). The first principal component (D1) showed the domination of loadings for the content of alcohols and aldehydes in greenhouse-dried grapes, regardless of whether it was a free or bound fraction. The second principal component (D2) contained mostly terpen and esters. In chamber-dried grapes, the dominant bound compounds were linalool, linalool oxide, and ethyl acetate. The PCA volatile composition distribution (Figure 1B) was informative regarding the changes in the measured parameters. The second quadrant contained the cluster of chamber-dried grapes (Figure 1A), which was related to the highest concentration of 6-methyl-5-heptene-2-one (1.24 ug/L free form) that was dominant in the bound fraction in both types of dried grapes (K2 (b) positioned in the first quadrant). All bound fractions of volatile aroma compounds were scattered in the first, second, and fourth quadrants (Figure 1B) in which dried grapes were positioned (Figure 1A). The presented PCA showed the domination of free fractions of volatile aroma compounds myrcene (T2), linalool (T5), linalool acetate (T12), and \(\beta\)-damascenone (\(\beta\)-dem). The clustering of these compounds was in agreement with the results of [PERSON] et al. [36].