## 2 Results and Discussion
### Evolution of C6 Volatiles in Grapes during Berry Development  
These C6 volatiles were clustered into three groups (Cluster 1, 2a,b) regarding their evolution similarity in these table grape cultivars during the berry development stages under both vintages (Figure 2). All the C6 aldehydes in these cultivars exhibited a similar evolution pattern (Cluster 2b in 2013 and Cluster 1 in 2014). For example, the C6 aldehydes in the \"Xiangfei\" cultivar remained at a high level during the veraison stage, followed by a dramatic increase during the harvest in 2014. The C6 aldehydes increased in concentration in the \"Moldova\", \"Tamina\", \"Italia\", and \"Muscat of Alexandria\" cultivars during the beginning stage of the veraison, followed by a concentration decrease before the harvest in the 2013 vintage. Regarding the individual C6 aldehydes, (_E_)-2-hexenal and hexanal showed an increase during berry maturation, followed by a decrease at the harvest in most of the cultivars in 2013. A similar evolution pattern of these aldehydes was also observed in Riesling and Cabernet Sauvignon grapes [24]. In 2014, these aldehydes did not decrease their concentration in \"Tamina\" and \"Italia\" before the harvest stage.  
Most of the C6 alcohols were grouped into Cluster 2a in these table grape cultivars under these two vintages (Figure 2). The C6 alcohols in the \"Xiangfei\" cultivar exhibited increased levels during  
Figure 2: Heat maps of C6 volatiles in different table grape cultivars during berry development in 2013 and 2014. “Zmgx” represents the “Zaomeiguixiang” cultivar. “Alexandria” represents the “Muscat of Alexandria” cultivar.  
berry development, followed by a dramatic reduction at the harvest in 2013. In the 2014 vintage, only 1-hexanol, (_E_)-2-hexen-1-ol, and the total C6 alcohols showed a similar evolution pattern (Cluster 2a). It has been reported that 1-hexanol and (_E_)-2-hexen-1-ol showed an increased level and then a decrease pattern in the 'Jingxiu' table grape cultivar during berry development, whereas a continuous accumulation of 1-hexanol was found in the Riesling and Cabernet Sauvignon cultivars [24, 31]. The C6 alcohols in the \"Moldova\", \"Tamina\", \"Italia\", \"Muscat of Alexandria\", and \"Christmas Rose\" cultivars continued to accumulate through the veraison to the harvest stage in the 2013 vintage. However, the C6 alcohol content showed a decreasing pattern in the \"Tamina\", \"Italia\", and \"Muscat of Alexandria\" cultivars during berry development under the 2014 vintage. The \"Zaomeiguixiang\" cultivar exhibited a continuous decrease in the C6 alcohols during the berry development period in 2013. However, its alcohol content was relatively stable in the 2014 vintage.  
The C6 esters in these cultivars during the development were assembled in Clusters 1 and 2a in the 2013 vintage, whereas they were grouped into Cluster 2b under the 2014 vintage (Figure 2). It was observed that these esters rapidly accumulated at the early stage of development, followed by a decrease at the harvest stage in both vintages. Such a trend was more obvious in the \"Moldova\" and \"Muscat of Alexandria\" cultivars. Our observation was consistent with previous reports [18, 24]. Regarding hexanoic acid (the only C6 acid detected in these cultivars), it showed an increase and then a decrease in its level during the maturation period in these cultivars, especially \"Xiangfei\" and \"Tamina\", under the 2013 vintage. In 2014, a similar evolution pattern was also found in the \"Xiangfei\" and \"Muscat of Alexandria\" cultivars. It should be noted that an increase of hexanoic acid was observed in the \"Tamina\" cultivar before the harvest.