# Monoterpenoids Evolution and MEP Pathway Gene Expression Profiles in Seven Table Grape Varieties
## 2 Results and Discussion  
### Monoterpenoids Content, Flavour Contribution, Variety and Season Effect  
Monoterpenoids were found accumulated in the berries during the grape development stages, and their contents at fully maturity stage would determine the overall Muscat aroma of grape berries. Therefore, it is important to study their concentration at harvest point. In this study, there were 25 monoterpenoids found in these seven table grapes at harvest. (Tables 1 and 2). According to their structures, these compounds included 1 cyclic acid: geramic acid; 5 cyclic alkenes: \(\beta\)_trans_-ocimee, \(\beta\)_cis_-ocimee, allo-ocimee, (_trans_cis_)-allo-ocimee, \(\beta\)-myrceme; 6 cyclic alcohols: linalool, isogenariol, nerol, \(\beta\)-citronellol, geraniol, \(\gamma\)-geraniol; 3 cyclic aldehydes: neral, citronellal, geraniol; 6 ethers: _cis_-pyran linalool oxide, _trans_-rose oxide, nerol oxide, _cis_-furan linalool oxide, _cis_-furan linalool oxide, _cis_-rose oxide, _trans_-furan linalool oxide; 3 acyclic alkenes: \(\gamma\)-terpinen, limonene, terpinolene; 2 acyclic alcohols: \(\alpha\)-terpineol, 4-terpineol. According to the research of [PERSON] [25], the existence of rose oxides was significantly related to the Muscat flavor, rose oxides could be detected in all the Muscat type varieties while not in neutral flavor varieties, the results of this study validated the above research. Meanwhile, our results were consistent with this study. Both _trans_-rose oxide and _cis_-rose oxide could be identified at harvest time (E-L38) in the five Muscat varieties of 'Xiangfei', 'Tamina', 'Italia', 'Zaomeiguixiang', and 'Muscat of Alexandria'. It was worth noticing that only around 20 monoterponids were detected in 'Moldova' at ripening, and all the 25 monoterponids were detected in 'Christmas Rose'; but four compounds including (_E_)-\(\beta\)-ocimene, _cis_-pyran linalool oxide, and especially _cis_-rose oxide and _trans_-rose oxide were in trace content and could not be quantified in these two neutral varieties. Total monoterpenoid concentrations were highest in the 'Xiangfei' variety in both seasons of harvest (785.86 \(\upmu\)g/L in 2013 and 1216.38 \(\upmu\)g/L in 2014), then followed by the five variety of 'Italia', 'Zaomeiguixiang', 'Christmas Rose', 'Tamina', and 'Muscat of Alexandria', whereas the ripen 'Moldova' variety exhibited the least content (12.36 \(\upmu\)g/L in 2013 and 0.75 \(\upmu\)g/L in 2014). Regarding the alcohols, linalool and geraniol were the most abundant compounds while 4-terpineol, nerol and isogenaniol had the lowest concentration in both seasons; total alcohol concentration in 2014 was higher than in 2013. In terms of alkenes, all the eight detected alkenes were at very low level or not detected in 'Moldova' and 'Christmas Rose', and the concentration of them in the other five varieties ranged from 0.04-22.12 \(\upmu\)g/L; 'Italia' and 'Zaomeiguixiang' had the similar content of alkenes in 2014. 'Xiangfei' had the most abundant of _trans_-furan linalool oxide and _cis_-furan linalool oxide in both seasons. For the two rose oxides, _trans_-rose oxide and _cis_-rose oxide were not detected in 'Moldova' and 'Christmas Rose', and even not abundant in the other five Muscat varieties, but they could contribute to the rose flavor due to the low odor threshold (0.5 \(\upmu\)g/L). Regarding the 3 aldehydes, 'Xiangfei' had the most abundant of citroncellal, while 'Zaomeiguixiang' had the most abundant of oral and geraniol; all the three aldehydes were not detected in the varieties of 'Moldova' and 'Christmas Rose' in 2014. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Compounds** & **Moldova** & \begin{tabular}{c} **Christmas** \\ **Rose** \\ \end{tabular}