## 3 Result
### Volatile Free Aroma Composition
Nerol was not detected in the four treatment groups at 49 DAA, and nerol accumulation in the GF treatment group was significantly higher compared to the control throughout the ripening period. Similarly, this was also true for the other aroma active compounds, such as geraniol and citronellol. Furthermore, myrcenol, hotrienol, phellandrene and \(\alpha\)-thujene in the berries of the GF group accumulated 1.08, 1.36, 1.49 and 2.72-fold compared with those of the control group at harvest, respectively. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Compounds** & **Odor Threshold** & **Odorant Series** & **Compounds** & **Odor Threshold** & **Odorant Series** \\ \hline \multicolumn{6}{c}{**C6 compounds**} & \multicolumn{4}{c}{**Esters**} \\ Hexanal & 16b [36] & 1 & Ethyl isothiytrate & 15b [37] & 3 \\
3-Hexanal & 0.25a [38] & 1 & Ethylbutanode & 600b [39] & 5 \\ (E)-2-Hexanal & 17a [36] & 1 & Butyl acetate & 66a [40] & 3 \\ Hexanal & 130b [36] & 1, 2 & Ethyl Hexanoate & 100b [39] & 3 \\ (Z)-3-Hexen-1-ol & 400b [36] & 1, 6 & Hexyl acetate & 670b [41] & 1,2,3 \\ (E)-2-Hexen-1-ol & 400b [36] & 1 & Ethyl heptanoate & 300b [39] & 3 \\ Alcohols & \multicolumn{4}{c}{Methyl salicate} & 40a [42] & 1,4 \\
1-Octen-3-ol & 1a [43] & 8 & **Terpenes** & & \\
2-Heptanol & 70a [42] & 3 & Nerolol & 500b [36] & 1,2 \\
2-Ethyl hexanol & 270a [44] & 2 & Linalool & 15b [36] & 2,3,5 \\ Octanol & 120b [45] & 2 & Geraniol & 30b [36] & 2 \\ Nonanol & 1000a [42] & 2 & Citronello & 100b [39] & 2 \\ Phenylethyl Alcohol & 1100a [6] & 2 & 4-Terpineol & 500b [41] & 1 \\
**Aldehydes** & \multicolumn{4}{c}{**Acids**} \\ Octanal & 50b [39] & 1, 2, 3, 6 & Hexanoic acid & 8500b [39] & 6 \\ Nonanal & 1a [45] & 1, 3 & Octanoic acid & 10,000b [41] & 5,6 \\ Benzaldehyde & 2000b [45] & 2, 3, 5, 7 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Odor threshold (\(\mu\)g/L) and odorant series of partial aroma compounds. Odorant series: 1, herbaceous; 2, floral; 3, fruity; 4, spicy; 5, sweet; 6, fatty; 7, roasty; 8, earthy. a: determined in water solution. b: determined in ethanol-water solution. By counting the number of volatile compounds of different treatments at harvest (Table 3), we found that GF treatment was able to increase the complexity of volatile composition significantly, most notably in terpene and ester compounds. The opposite phenomenon was observed after G treatment, where the number of acid, ester and alcohol compounds was decreased compared with CK. Additionally, the effect of each treatment was unobvious in the number of aldehyde, acid and alcohol compounds. By comparing the sum of the various types of substances in the four treatment groups (Table 4), we found that the F treatment can promote the accumulation of esters and alcohols, and that the G treatment only increased the accumulation of aldehydes compared to the control, but that the combined GF treatment increased the concentrations of all aroma substance categories. Additionally, the total concentrations of aroma compounds after G, F and GF treatments were all higher relative to the control (Table 4), which were mainly contributed due to the increase in aldehydes. Taken together, the data indicated that the different treatments had significant but differential effects on the aroma characteristics of table grapes at harvest.