## 2 Results and Discussion  
### C6 Volatile Level, Odor Contribution, and Cultivar and Vintage Effect  
C6 volatile compounds are accumulated in grape berries along with the berry development stages, and their level in ripened grape berries determines the overall aroma [18; 24; 26]. In the present study, a total of 11 C6 volatiles were detected in these table grapes at harvest. Regarding their chemical feature, these C6 volatiles included two aldehydes, five alcohols, three esters, and one acid under these two vintages (Figure 1). The highest concentration of the total C6 volatile compounds was found in the \"Xiangfei\" cultivar at the harvest under both vintages, whereas the ripen \"Christmas Rose\" cultivar exhibited the least content, especially in 2013. Regarding the C6 aldehydes, hexanal and (\(E\))-2-hexenal were found in all table grapes at harvest, and these two aldehydes appeared to be the dominant C6 volatiles. The concentration of these two aldehydes in these ripenedgrapes ranged between 1-5 mg/L and 2-10 mg/L, respectively, which was significantly higher than their odor threshold (4.5 \(\upmu\)g/L and 17 \(\upmu\)g/L, [32]). This indicated that their greenish and fruity flavor notes could significantly affect the overall aroma of these table grapes [21]. It has been reported that C6 aldehydes also played important roles in affecting the aromatic feature of other fruits due to their high concentration [19; 20]. Among these ripenedtable grape samples, the \"Xiangfei\" cultivar was found to exhibit the highest level of these C6 aldehydes in both the 2013 and 2014 vintages, whereas the lowest level of these aldehydes were observed in the \"Christmas Rose\" cultivar at the ripening stage in 2013 (Figure 1a). In terms of the C6 alcohols, all the table grape cultivars contained these five individual C6 alcohols in both vintages (except for (\(Z\))-2-hexen-1-ol in 2014) at harvest (Figure 1b). The \"Moldova\" cultivar exhibited the highest level of total C6 alcohols, whereas the lowest was found in the \"Muscat of Alexandria\" cultivar at harvest in both vintages. Meanwhile, the 2013 ripenedgrape cultivars possessed a higher concentration of the total C6 alcohols than those harvested in 2014. (\(E\))-2-hexen-1-ol appeared to be the dominant C6 alcohol in these grapes, which was different to some wine-making grapes [18, 26]. Additionally, these table grape cultivars at the harvest contained a higher content of (\(E\))-2-hexen-1-ol than (\(Z\))-3-hexen-1-ol. Similar reports were also observed in other table grape cultivars [17, 31]. Among these table grape cultivars, the \"Tamina\" and \"Moldova\" cultivars in the 2013 vintage showed the highest concentration of (\(E\))-2-hexen-1-ol, 1-hexanol and (\(E\))-3-hexen-1-ol, whereas  
Figure 1: Concentrations of volatile compounds and their odor threshold values in different table grape cultivars at harvest. (**a**) C6 aldehydes; (**b**) C6 alcohols; (**c**) C6 acid; and (**d**) C6 esters. Different letters mean significant differences according to the Duncan test (\(p<0.05\)) in individual vintages. “Zmgx” represents the “Zaomeiguixiang” cultivar; “Alexandria” represents the “Muscat of Alexandria” cultivar; OTV is the odor threshold value. (\(Z\))-3-hexen-1-ol was more present in the \"Muscat of Alexandria\" and \"Christmas Rose\" cultivars. C6 alcohols have been reported to have herbaceous, grassy, green, and leaf-like scents [33; 34]. In these grape cultivars, 1-hexanol and (\(E\))-3-hexen-1-ol did not have a concentration higher than their odor threshold, indicating that these volatiles could provide a limited contribution to the overall aroma of these grapes. However, (\(E\))-2-hexen-1-ol exhibited a concentration higher than the threshold in these table grapes, demonstrating that its flavor notes could be incorporated in the aromatic features of these grapes. It should be noted that the flavor contribution of (\(Z\))-3-hexen-1-ol varied in these grapes.