## Results
### Effect of Dealcoholization on Volatile Compounds
#### 3.2.2 Higher Alcohols  
Higher alcohols are produced as by-products of alcoholic yeast fermentation. They are produced mainly by the Ehrlich pathway, in which amino acids are used as substrates for transamination and decarboxylation before being reduced by alcohol dehydrogenase. In addition, yeasts can also produce higher alcohols from carbon fragments of sugar metabolism [81]. Higher alcohols at concentrations less than 300 mg/L (300,000 \(\upmu\)g/L)contribute to the desirable wine aroma, but at concentrations greater than 400 mg/L (400,000 \(\upmu\)g/L), a detrimental effect was observed [82; 83]. In this study, the total concentration of higher alcohols in all original and dealcoholized wines ranged from 199 \(\upmu\)g/L to 9705 \(\upmu\)g/L, with no concentration exceeding 400,000 \(\upmu\)g/L, so no undesirable aroma was perceived in both original and dealcoholized wines. However, the degree of dealcoholization by RO or VD was shown to affect the loss of higher alcohols in the wine. The removal of 4.2% ethanol from Montepulciano d'Abruzzo red wine (13.2% \(v/v\)) by RO resulted in a loss of 30% of the total concentration of higher alcohols [52]. Dealcoholization of a Verduno Pelaverga red wine (14.6% \(v/v\)) at 5% \(v/v\) also resulted in a loss of higher alcohol content of about 53% [13]. In the current study, where alcohol content was reduced to 0.7% \(v/v\), the majority of higher alcohols were still present in both the original and dealcoholized wines (despite losses), with 1-pentanol being the most abundant (1 \(\upmu\)g/L to 6306 \(\upmu\)g/L), followed by 2-phenylethanol (185 \(\upmu\)g/L to 2785 \(\upmu\)g/L), but at concentrations below the odor threshold, especially in RO and VD dealcoholized wines. RO resulted in 67%, 58% and 75% losses in the total concentration of higher alcohols in white, rose, and red wines, respectively, while VD caused about 95%, 85% and 94% losses in white, rose, and red wines, respectively. VD resulted in the complete removal of some higher alcohols in dealcoholized white wine (including benzyl alcohol, _cis_-3-hexen-1-ol, 3-ethoxy-1-propanol, and isobutanol), dealcoholized rose wine (i.e., 1-undecanol, 1-decanol, 2-ethyl-1-hexanol, and isobutanol), and dealcoholized red wine (including 1-decanol, 2-ethyl-1-hexanol, 1-hexanol, isobutanol, and 4-methyl-1-pentanol). On the other hand, the content of isobutanol, 3-ethoxy-1-propanol, and 1-heptanol remained almost unchanged after dealcoholization by RO (especially in dealcoholized white wine), while 2-ethyl-1-hexanol increased by 55% and 4% in RO dealcoholized rose and red wines, respectively. In contrast, in a similar study in which Langhe Rose wine, Barbera red wine, and Verduno Pelaverga red wine were dealcoholized at 5% \(v/v\) ethanol using the membrane contactor technique, higher losses of isobutanol (between 72% and 75%) were reported [13]. Moreover, [PERSON] et al. [16] observed no change in 1-hexanol concentration in wine fractions dealcoholized by 6.5% alcohol using osmotic distillation, while in this study the concentration of 1-hexanol was significantly reduced in all wines after dealcoholization by RO and VD. In agreement with our results, other studies found losses of 5% to 15% 1-hexanol in red wines dealcoholized by 2.5% alcohol by RO-EP [50], 84% losses in Chardonnay wine dealcoholized by 10.61% \(v/v\) ethanol using vacuum distillation [14], 66% to 71% losses in wines (Langhe Rose, Barbera red, and Verduno Pelaverga wines) dealcoholized at 5% alcohol by RO and VD [13], 17% to 35% losses in white and red wines dealcoholized by 4% alcohol by a membrane contactor [74], and 28% to 38% losses in Aglianico wines dealcoholized by 5% alcohol with an osmotic distillation method [8]. In the later studies, losses of 1-hexanol increased with the degree of dealcoholization [8; 74]. The finding of our study shows that RO is more effective than VD for higher alcohol retention.