## Results
### Effect of Dealcoholization on Volatile Compounds
#### 3.2.1 Esters
A decrease in ethyl ester concentrations  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c} \hline \multirow{2}{*}{**Compounds**} & **RI** & \multicolumn{3}{c}{**White Wine**} & \multicolumn{3}{c}{**Rosé Wine**} & \multicolumn{3}{c}{**Red Wine**} & \multicolumn{3}{c}{**Odor**} & \multirow{2}{*}{**Threshold**} & \multirow{2}{*}{**Aroma**} \\  & **DB-** & & & & & & & & & & & & **(ug/L)*** \\ \cline{1-1}  & **WAX** & **CK** & **RO** & **VD** & **CK** & **RO** & **VD** & **CK** & **RO** & **VD** & **Descriptor*** & **(ug/L)*** \\ \hline Nerbild & 2039 & 14\({}^{\ast}\) & 3\({}^{\text{\text{\  
was also observed when red wine was partially dealcoholized by RO-EP, with higher molecular weight ethyl esters, such as ethyl octanoate and ethyl decanoate, decreasing the most, although smaller and more volatile esters were expected to permeate the RO membrane [50]. The significant losses in esters may not be solely due to their hydrophobic nature, as suggested by [PERSON] et al. [22] and [PERSON] et al. [16], or by membrane filtration, but the removal of ethanol may also have affected their ester equilibrium (Equation (1)) through esterification and hydrolysis reactions, such that the esters underwent hydrolysis to release ethanol and their corresponding acids [50]. Previous studies have found that esters with higher molecular weights are hydrolyzed more rapidly [57]. Partial dealcoholization of red wine using RO-EP resulted in a decrease in ethyl ester concentrations, with higher molecular weight esters (ethyl octanoate and ethyl decanoate) decreasing more than smaller and more volatile esters such as ethyl propanoate and ethyl butanoate, which was attributed to ethanol reduction, membrane filtration, and shift in ester equilibrium [50]. In addition, the concentrations of straight-chain ethyl esters such as ethyl hexanoate, octanoate, and decanoate were found to decrease during wine ageing, which was attributed to their enzymatic production exceeding their equilibrium concentrations during fermentation [75]. Further investigation of tartaric acid esterification with ethanol in a model wine showed the influence of ethanol concentration, with higher ethanol concentrations increasing both the rate and amount of ester formation [76]. Moreover, esterification rates were found to decrease with increasing molecular weight, in the following order: ethyl decanoate > ethyl octanoate > ethyl hexanoate [73]. Subsequently, when a polypropylene hollow fiber membrane contactor apparatus was used to remove 2%, 3% and 5% \(v/v\) ethanol from two red wines with different initial ethanol concentrations (13.3% and 15.4% \(v/v\)), losses equal to 11-100% were observed in ethyl ester concentration [8]. [PERSON] et al. [77] also found a decrease up to 80% in ethyl ester concentration when the ethanol concentration of Shiraz wine (with 13.7% \(v/v\) ethanol) and Chardonnay wine (with 12.2% \(v/v\) ethanol) decreased by up to 5% \(v/v\) during dealcoholization with a benchtop system RO-EP. Similar results were recently observed by [PERSON] et al. [50] after dealcoholization of Shiraz Cabernet Sauvignon, Cabernet Sauvignon, and Shiraz wines by 1.6%, 2.6% and 0.7% \(v/v\) ethanol, respectively, using the reverse RO-EP. Interestingly, in these studies, the concentrations of some acids such as propanoic, decanoic, and hexanoic acids increased by 11% to 173% [77], 6% to 25% [50], and 24% [8], respectively, which may indicate ester hydrolysis. Although both RO and VD resulted in significant ester losses, our results show that RO retains more esters than VD, which could be due to the ability of RO membrane to retain low molecular weight compounds due to its small pore size and molecular weight cutoff (MWCO) value, although this may result in severe membrane fouling and higher energy consumption [78; 79]. Moreover, the temperature used in VD (35 \({}^{\circ}\)C) might have led to a greater loss of esters, as high temperature causes higher evaporation and thermal degradation of volatiles and other wine components.