## 3 Results and Discussion
### Accumulation of Ester Compounds during the Simulated Fermentation of Blueberry Wine  
Our results show that, compared with the pure fermentation of _S. cerevisiae_ NCUF309.2, the co-fermentation of _S. cerevisiae_ NCUF309.2 and C. _glabrata_ NCUF308.1 or _P. anomula_ NCUF306.1 could significantly increase the contents of ester compounds (_p_ < 0.05), which were 3.29, 5.57, 2.34, 1.50, 4.75, and 2.41 times that of S sample, respectively (Figure 5). This could be related to species belonging to the genera of _Candida_ and _Pichia_, with a strong capacity to produce ester compounds [36]. Anyway, in the WS samples, the contents of ester compounds significantly increased only in the sample of WS5, which were 3.04 times  
Figure 4: The contents of ethanol and reducing sugar of different ester-producing yeasts with _S. cerevisiae_ NCUF309.2 at different ratios on 7 d of simulated fermentation of blueberry wine. (The content of reducing sugar is on the left, and the content of ethanol is on the right. Different letters represent significantly different (_p_ < 0.05)). that of the S sample. The production of ester compounds mainly occurred in the middle and late stages of fermentation. However, in the samples of WS1 and WS10, the population of _W. anomalous_ NCUF307.1 in these stages was rare or even absent, resulting in a low content of ester compounds in the samples. Ester compounds can be further categorized into acetate esters, ethyl esters, and other esters [37]. Both acetate esters and ethyl esters are of key importance in the whole wine flavor, impressing a positive contribution by distinct sensory notes: sweet-fruity, grape-like odor, and sweet-balsamic [38]. In the co-fermentation samples of CS, the contents of acetate esters and ethyl esters both significantly increased, and the content of ethyl esters was higher in the CS5 sample, while the content of acetate esters was higher in the CS1 sample (Figure 5). Additionally, in the co-fermentation samples of PS, the content of ethyl esters was higher in the PS5 sample, while the content of acetate esters was higher in the PS10 sample. These results indicated that the ratio of ester-producing yeast co-fermentation with _S. cerevisiae_ had an effect on the formation of ester compounds during fermentation. [PERSON] et al. also found that _W. saturnus_ and _S. cerevisiae_ could produce a higher content of acetate esters at the ratio of 10:1, while they could produce more ethyl esters at the ratio of 1:1 and 1:10 [39]. In the co-fermentation samples of WS, the contents of acetate esters and ethyl esters both significantly increased in only the WS5 sample. Anyway, the contents of other esters were also significantly increased in the co-fermentation samples (except the samples of PS1 and WS10), and the highest content was in the WS5 sample. As for acetate esters, ethyl acetate, phenethyl acetate, and isoamyl acetate were the main acetate esters (Table 1). Additionally, their contents both increased in the co-fermentation samples of CS and PS, while both increased in the co-fermentation samples of WS5 and WS10. [PERSON] et al. also found the contents of ethyl acetate, isoamyl acetate, and phenethyl acetate increased in the co-fermentation samples, compared with those of _S. cerevisiae_ pure fermentation [40]. Ethyl acetate could improve the aroma complexity of fruit wine, and phenethyl acetate and isoamyl acetate were recognized as important flavor compounds to contribute to the fruity flavor of fruit wine [41; 42]. These results suggested that co-fermentation could improve the acetate contents, especially the contents of ethyl acetate, isoamyl acetate, and phenethyl acetates, compared with those of _S. cerevisiae_ pure fermentation, which would be favorable to the flavor of blueberry wine. Figure 5: Contents of ester compounds of different ester-producing yeasts, with _S. cerevisiae_ NCUF309.2 at different ratios during simulated fermentation of blueberry wine. (Different letters represent significantly different (\(p<0.05\))).