## 2 Results
### Aroma Compounds Retention  
Aroma compounds identified in initial Cabernet Sauvignon red wine and retentate obtained by reverse osmosis and nanofiltration, and their retention indices and odour descriptions are shown in Table 3.  
For better display, all 47 volatile compounds were divided into six groups (acids, alcohols, carbonyl compounds, terpenes, esters and volatile phenols). These compounds are characteristic of red wine, especially Cabernet Sauvignon wine variety, as shown in previous studies [30; 31]. Concentrations of individual compounds in initial wine and obtained retentates are presented in Tables 4 and 5. Seven acids (acetic, octanoic, nonanoic, decanoic, lauric, myrsistic and palmitic acid) were identified in initial wine and retentates, where the acetic acid had the highest concentration (682.5 \(\upmu\)g/L) in initial wine. After membrane filtration treatment, all obtained retentates contained significantly lower amounts of acetic acid. The lowest concentration among RO retentates was evaluated at 2.5 MPa without cooling, meaning that the decrease of pressure and increase of temperature lowered the acetic acid retention. The increase of transmembrane pressure resulted in higher retention of acetic acid, and the highest concentration were evaluated at 4.5 MPa (428.7 \(\upmu\)g/L) and 5.5 MPa (436.4 \(\upmu\)g/L) with cooling in RO retentates. NF retentates contained lower concentrations of acetic acid than RO retentates, with highest one obtained at 5.5 MPa with cooling, 365.8 \(\upmu\)g/L. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Compound** & **LRI** & **Odour** & **Compound** & **LRI** & **Odour** \\ \hline Acids & \multicolumn{4}{c}{Esters} \\ Acetic acid & 622 & vinegar & Ethyl hexanoate & 997 & fruity \\ Octanoic acid & 1199 & fatty & Ethyl 4-hydroxybutanoate & 1060 & caramellic \\ Nonanoic acid & 1265 & fatty & Diethyl succinate & 1179 & fruity \\ Decanoic acid & 1376 & fatty & Ethyl octanoate & 1191 & fruity \\ Lauric acid & 1556 & fatty & Ethyl hydrogen succinate & 1198 & faint \\ Myristic acid & 1749 & fatty & Phenethyl acetate & 1248 & floral \\ Palmitic acid & 2004 & fatty & Ethyl decanoate & 1391 & fruity \\ Alcohols & \multicolumn{4}{c}{Ethyl vanillate} & 1580 & smoky \\ Isoamyl alcohol & 734 & fruity & Ethyl laurate & 1584 & fatty \\
1-butanol & 752 & fused oil & Hexyl salicate & 1667 & green \\
2,3-butanedol & 804 & fruity & Ethyl myrsistate & 1778 & fatty \\
1-hexanol & 868 & green & Disobutyl phthalate & 1859 & faint \\ Methionol & 981 & sulphurous & Ethyl pentadecanoate & 1880 & honey \\ Benzyl alcohol & 1037 & fruity & Methyl palmit & 1907 & fatty \\
1-octanol & 1071 & green & Dibutyl phthalate & 1953 & faint \\
2-phenylethanol & 1103 & floral & Ethyl palmitate & 1978 & fatty \\ Dodecanol & 1469 & fatty & Ethyl linoleate & 2146 & fatty \\ Carbonyl compounds & \multicolumn{4}{c}{Ethyl oleate} & 2152 & fatty \\
4-propylenzaldehyde & 1261 & faint & Ethyl scareate & 2176 & fatty \\ Geranyl acetone & 1448 & floral & Volatile phenols & \\ Lily aldehyde & 1517 & floral & 4-ethylphenol & 1166 & smoky \\ Hexyl cinnamaldehyde & 1738 & floral & 4-ethylguaiacol & 1268 & smoky \\ Terpenes & \multicolumn{4}{c}{2,4-Di-T-butylphenol} & 1501 & faint \\ \(\alpha\)-terpinolene & 1092 & citrus & & \\ Nerol & 1218 & citrus & & \\ \(\beta\)-citronellol & 1223 & citrus & & \\ \(\beta\)-damascenone & 1377 & fruity & & \\ Phenanthrene & 1772 & faint & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Linear retention indices (LRI) and odour description of volatile compounds identified in Cabernet Sauvignon wine variety and retentates obtained by reverse osmosis and nanofiltration at 2.5, 3.5, 4.5 and 5.5 MPa with and without cooling.