## 3 Results and Discussion
### Analysis of VOCs in Base Wines
The volatile composition of the wines aged on ultrasound-untreated lees (L) and the control wine (C) displayed high values for 10 VOCs, accounting for 17% of total VOCs, although without statistically significant differences with the group of wines aged on sonicated lees. These compounds are the following: three methyl esters (3-methylbutyl octanoate, methyl decanoate and 3-methylbutyl decanoate) and five long-chain ethyl esters (ethyl decanoate, ethyl dodecanoate, ethyl tetradecanoate, ethyl pentadecanoate and ethyl hexadecanoate), volatile compounds with a soapy, oily or wax odour [26], nonan-1-ol (green odour) and nonanal (soap-like odour) [27]. No statistically significant differences in volatile composition could be observed between both wines (samples C and L). This behaviour, found also in wine physico-chemical composition, may be explained by the fact that the ageing treatment was not intense enough, either because the ageing conditions (temperature, contact time of the lees with wine, lees stirring, etc.) were mild or because the concentration of lees was low. However, it seems that the most intense ultrasound treatment increased yeast autolysis, as an enhanced concentration of polysaccharides was observed in the wine aged on sonicated lees at 90% (Table 1). Regarding the amplitude used during treatment of lees by ultrasound, wines aged with lees treated at 60% and 90% of amplitude (samples 60 and 90, respectively) showed high values for most of the VOCs located in the first quadrant of the PCA score plot (Figure 2). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Code**} & \multirow{2}{*}{**Parameters**} & \multirow{2}{*}{**Control (C)**} & \multirow{2}{*}{**Lees (L)**} & \multicolumn{3}{c}{**Ultrasound-Treated Lees**} \\ \cline{5-6}  & & & & **30\%** & **60\%** & **90\%** \\ \hline Phe2 & 4-ethylphenol & 0.184 \(\pm\) 0.018 \({}^{\mathrm{a}}\) & 0.217 \(\pm\) 0.125 \({}^{\mathrm{a}}\) & 0.243 \(\pm\) 0.020 \({}^{\mathrm{a}}\) & 0.309 \(\pm\) 0.014 \({}^{\mathrm{ab}}\) & 0.245 \(\pm\) 0.067 \({}^{\mathrm{a}}\) \\ Phe3 & 4-ethyl-2-methoxyphenol & 0.069 \(\pm\) 0.011 & 0.098 \(\pm\) 0.027 & 0.089 \(\pm\) 0.012 & 0.120 \(\pm\) 0.004 & 0.100 \(\pm\) 0.037 \\ Phe4 & 2,4-ditter-butylphenol & 0.085 \(\pm\) 0.021 & 0.077 \(\pm\) 0.013 & 0.134 \(\pm\) 0.063 & 0.117 \(\pm\) 0.043 & 0.121 \(\pm\) 0.045 \\ Phe5 & 1,1\({}^{\prime}\)-biphenyl & 0.010 \(\pm\) 0.002 \({}^{\mathrm{a}}\) & 0.011 \(\pm\) 0.003 \({}^{\mathrm{a}}\) & 0.020 \(\pm\) 0.003 \({}^{\mathrm{b}}\) & 0.018 \(\pm\) 0.005 \({}^{\mathrm{b}}\) & 0.018 \(\pm\) 0.004 \({}^{\mathrm{b}}\) \\ Ald1 & Acetaldehyde & 0.122 \(\pm\) 0.024 & 0.100 \(\pm\) 0.032 & 0.186 \(\pm\) 0.082 & 0.149 \(\pm\) 0.006 & 0.152 \(\pm\) 0.049 \\ Ald2 & Nonanal & 0.036 \(\pm\) 0.006 & 0.025 \(\pm\) 0.003 & 0.021 \(\pm\) 0.003 & 0.024 \(\pm\) 0.006 & 0.021 \(\pm\) 0.008 \\ Ke1 & Octan-2-one & 0.014 \(\pm\) 0.002 \({}^{\mathrm{a}}\) & 0.013 \(\pm\) 0.003 \({}^{\mathrm{a}}\) & 0.021 \(\pm\) 0.002 \({}^{\mathrm{b}}\) & 0.027 \(\pm\) 0.003 \({}^{\mathrm{c}}\) & 0.022 \(\pm\) 0.007 \({}^{\mathrm{b}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 2: Principal component analysis of wines and volatile compounds. Symbols. C: Control; L: Ultrasound-untreated lees; 30, 60, 90: ultrasound-treated at an amplitude level of 30%, 60%, and 90%, respectively. Code of volatile compounds (see Table 2). Statistically significant higher concentrations of four acetates (ethyl, 3-methylbutyl, ethyl 2-phenyl and 2-phenyled acetate), four short-medium chain esters (diethyl butane-dioate, ethyl 2-hydroxypropanoate, ethyl 4-hydroxybutanoate and ethyl hexanoate), ethyl benzoate, ethyl furan-2-carboxylate, and the two terpenes (3,7-dimethylocta-1,6-dien-3-ol(linalo) and 3,7-dimethyl-6-en-1-ol(citronellol)) were found in the wine aged on lees treated at the amplitude of 90% (sample 90) than in the control wine (sample C) and the wine aged on unsonicated lees (sample L) (Table 2). These compounds could contribute to the fruity and floral notes of the wine aroma [26].