# Effect of Deacidification Treatment on the Flavor Quality of Zaosu Pear-Kiwifruit Wine
## 3 Results and Discussion
### Effect of Deacidification on Aromatic Profile of Pear-Kiwifruit Wine  
A total of 77 volatiles were detected in all wine samples, from the following chemical classes: esters, higher alcohols, acids, terpenoids, norisoprenoids, aldehydes, ketones, and volatile phenols (Supplementary Table S5). Pear-kiwifruit juice and alcoholic fermented wine contained 59 and 61 volatile aromatic compounds, respectively, whereas MLF wine contained 64, and chemically deacidified wine contained 35 (Figure 4A). The total content of aromatic compounds in alcoholic fermented wine was higher than in chemically deacidified wine, but significantly lower than in MLF wine (Figure 4B). Esters were the dominant class of aromatic compounds in mixed juice and all wines, especially ethyl esters and acetate esters (Supplementary Table S5); isoamyl acetate, ethyl caproate, ethyl octanoate, and ethyl decanoate were the most abundant aromatic compounds in all treatments, accounting for \(>\)70% of the total ester concentration (Table 4); the highest total ester concentration (11,598 \(\mu\)g/L) was in MLF wine (Figure 4C). In agreement with these findings, MLF with _O. oeni_ also enhanced the total ester content of red wine [11; 25; 30; 31]. In this study, the contents of carboxylic acid and alcohol esterification substrates did not decrease after the formation of esters; it appears that the high glycosidase activity produced by GF-2 [13] promoted ester accumulation via the hydrolysis of glycoconjugates. In contrast, a significant decrease in ester content after MLF with a different _O. oeni_ strain was observed [30; 32], indicating that the evolution of esters during MLF with _O. oeni_ is strain-dependent and depends on the balance among esterification, ester hydrolysis, and glycoconjugate hydrolysis. Notably, ethyl lactate, a characteristic ester produced during MLF, was present only in MLF wine, and the total concentration of pear aromatic esters (i.e., methyl (\(2E\),\(AZ\))-deca-2,4-dienoate, ethyl (\(2E\),\(AZ\))-deca-2,4-dienoate, heptyl acetate, ethyl caprylate, and hexyl acetate) increased by 8.3% after MLF (Table 4). After chemical deacidification, 20 esters disappeared (Supplementary Table S5), the contents of others significantly decreased, and the total ester content decreased by about two-thirds (Figure 4C). This result confirms that the precipitation of organic acid salt formed in the process of chemical deacidification caused the loss of aromatic compounds in fruit wine [33]. Alcohols (other than ethanol) were the second largest group of volatiles in mixed juice and pear-kiwifruit wines, of which 1-pentanol, 1-hexanol, and 2-phenylethanol were dominant and contributed \(>\)94% of the total alcohol content (Supplementary Table S5). The total alcohol concentration increased by 13.3% after MLF (to 6125 \(\mu\)g/L) and decreased by \(\sim\)60% after chemical deacidification (to 2181 \(\mu\)g/L) (Figure 4D). During alcoholic fermentation, phenylalanine metabolism produces 2-phenylethanol, which has a rose/honey aroma [25; 34; 35]; this, however, cannot explain the accumulation of this compound in this study, considering the absence of sugar and nitrogen sources occurring in MLF. It is possible that glycoconjugate precursors in pear-kiwifruit wines were hydrolyzed by _O. oeni_GF-2 glycosidase, to release 2-phenylethanol. There was a significant increase previously found in 2,3-butanediol during MLF with _O. oeni_[6,12], in agreement with the finding here that the concentration of 2,3-butanediol increased eightfold after MLF (Table 4), conferring a complexity of aroma to the wine. The decreased concentration of citric acid after MLF (Figure 3A) suggested that GF-2 increased 2,3-butanediol formation through degradation of diacetyl, a product of citric acid metabolism.