## 4 Discussion  
In recent years, one of the most relevant concerns that is related to the winemaking sector is the progressive increase of ethanol content. Among microbiological strategies proposed to decrease alcohol level in wine is the use of non-_Saccharomyces_ yeasts in co-fermentation or sequential fermentation with _S. cerevisiae_ starter strains under aerobic and anaerobic conditions were proposed [24; 28; 29; 31; 32; 43; 44; 45; 46; 47; 48]. Several studies reported that the use of air flow during the early stage of fermentation affects yeast physiology and metabolism favouring the fermentation performance of yeasts [49; 50; 51; 52; 53]. In particular, in \begin{table}
\begin{tabular}{c c c c} \hline \hline
**mg/L** & \multicolumn{3}{c}{**Fermentation Trials**} \\ \hline \multirow{3}{*}{**ESTERS**} & _S. cerevisiae_ Pure & _S. bombicola_/_S. cerevisiae_ & _S. bombicola_/_S. cerevisiae_ semi anaerobic condition \\  & Culture & 20 mL/L/min & condition \\ \hline Ethyl butyrate & 0.41 \(\pm\) 0.02  & 1.08 \(\pm\) 0.35  & 0.40 \(\pm\) 0.39  \\ Ethyl acetate & 30.58 \(\pm\) 1.27  & 26.17 \(\pm\) 2.51  & 21.58 \(\pm\) 1.04  \\ Ethyl hexanoate & 0.06 \(\pm\) 0.004  & 0.04 \(\pm\) 0.011  & 0.03 \(\pm\) 0.019  \\ Isoamyl acetate & 2.017 \(\pm\) 0.05  & 0.91 \(\pm\) 0.34  & 2.71 \(\pm\) 1.18  \\ \hline
**ALCOHOLS** & \multirow{3}{*}{69.63 \(\pm\) 0.06  } & 33.74 \(\pm\) 0.31  \\ Isobutanol & 14.33 \(\pm\) 0.16  & 35.34 \(\pm\) 1.21  & 19.43 \(\pm\) 2.04  \\ Amyl alcohol & 4.89 \(\pm\) 1.77  & 3.82 \(\pm\) 0.28  & 1.30 \(\pm\) 0.24  \\ Isoamyl alcohol & 64.50 \(\pm\) 2.63  & 45.47 \(\pm\) 1.36  & 29.31 \(\pm\) 0.42  \\ \(\beta\)-Phenyl ethanol & 30.1 \(\pm\) 0.018  & 24.8 \(\pm\) 0.28  & 35.8 \(\pm\) 0.07  \\ \hline
**CARBONYL** & \multirow{3}{*}{10.59 \(\pm\) 0.19  } & \multirow{3}{*}{30.12 \(\pm\) 2.22  } & \multirow{3}{*}{9.26 \(\pm\) 0.53  } \\
**COMPOUNDS** & \multirow{3}{*}{10.08 \(\pm\) 0.01  } & \multirow{3}{*}{0.05 \(\pm\) 0.001  } & \multirow{3}{*}{0.12 \(\pm\) 0.05  } \\ Acetaldehyde & \multirow{3}{*}{0.09 \(\pm\) 0.018  } & \multirow{3}{*}{0.007 \(\pm\) 0.0004  } & \multirow{3}{*}{0.10 \(\pm\) 0.05  } \\
**MONOTERPENS** & \multirow{3}{*}{10.08 \(\pm\) 0.01  } & \multirow{3}{*}{0.05 \(\pm\) 0.001  } & \multirow{3}{*}{0.12 \(\pm\) 0.05  } \\ Linalool & 0.08 \(\pm\) 0.01  & 0.05 \(\pm\) 0.001  & 0.12 \(\pm\) 0.05  \\ Geraniol & 0.09 \(\pm\) 0.018  & 0.007 \(\pm\) 0.0004  & 0.10 \(\pm\) 0.05  \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The main volatile compounds of _S. cerevisiae_ pure culture and sequential fermentations with or without air flow addition. Data are means \(\pm\) standard deviations from three independent experiments. Data with different superscript letters (a,b,c) within each Column are different according to Duncan tests (0.05%). S. cerevisiae_ respiration is repressed by high concentrations of sugars even in the presence of oxygen, whereas in general non-_Saccharomyces_ wine yeasts are able to aerobically respire sugar, modulating the production of ethanol, glycerol and other by-products [28; 47; 54; 55; 56]. In this work, the effect of aeration on ethanol content, population dynamics and analytical profile of wines using free cells of _S. bombicola_/_S. cerevisiae_ sequential inoculation were evaluated. _S. bombicola_ strain, used in this work was investigated in a previous work in immobilized form and in anaerobic condition [32], determining an ethanol reduction of 1.6% (\(p/v\)) using 10% (\(w/w\)) of beads corresponding to an inoculation level of 10\({}^{8}\) cells/mL. Here, a comparable result was obtained (1.46% \(v/v\)) but with a lower inoculum of free cells (5 \(\times\) 10\({}^{7}\) cells/mL) and in presence of initial concentration of 10\({}^{4}\) cells/mL of WNS. Free cell inoculation is an easily procedure to apply at industrial level in winemaking sector in comparison to the use of immobilized cells that in the other side allows high inoculum level.