## 2 Results and Discussion
### Expression of Genes Related to Volatile Compounds Formation
Strikingly, the expressions of all genes involved in fatty acid metabolism (_FAT1_, _ACC1_, _FAS1_, _FAS2_, _ELO1_, and _OLE1_) were significantly repressed by high UFAs addition (120 and 240 mg/L) during fermentation, especially LA and ALA samples. This explained the marked reduction of MCFAs contents in these wines relative to the control. _OLE1_ encodes delta (9) fatty acid desaturase and it is responsible for catalyzing FAs form UFAs. Exogenous UFAs expressed the expression of _OLE1_ significantly because cells do not need de novo synthesis of UFAs from MCFAs and FAs [33]. Similar results were found in the present study. _ATF1_ encodes the alcohol acetyl transferase (AATases) and it is involved in the biosynthesis of acetate ester [7; 34]. Its expression is positive with the production of acetate esters in wine. Exogenous UFAs can repress the expression of _ATF1_ and results in decrement of acetate esters in wine [35]. Similar phenomena were observed in 120 and 240 mg/L OA and LA addition wines (OA_120, OA_240, LA_120, and LA_240), as well as all ALA addition wines (Figure 5). However, no continuous and significant expressive effects on _ATF1_ expression were observed in OA_12, OA_60, and LA_12 fermentation, conversely, slight increased expressions were found in the early phase of OA_12 and LA_12 fermentation, and the late phase of OA_60 fermentation relative to the control, respectively,  
Figure 5: (**A**) Metabolic pathway involved in volatile compounds formation. Yeast genes that are involved in each step in the different pathways are shown in italic. (**B**) Comparative analysis of genes expressions of yeast in different treatments with that in the Control at each fermentation stage (sugar consumption 20%, 50%, and 80%) were conducted. The ratios were obtained using the corresponding Control as reference (red up-regulated and green down-regulated). which might, at least partially, account for increased productions of acetate esters in these wines (Figure 3, Figure 5). At present, we cannot exclusively ascribe these increments to the up-regulation of ATF1, because increased number of cells could also result in the accumulation of acetate esters [15]. Exogenous UFAs can result in the inhibition of biosynthesis of acetate esters [12; 14]. Our data indicated that the inhibition is mainly occurred in the higher concentrations of OA and LA and ALA added fermentations (Figure 3). In contrast to acetate ester production, the formation of MCFA ethyl ester is more complicated. The rate of MCFA ethyl ester formation is dependent on the concentration of the two substrates (the acyl-CoA component and ethanol) and the total activity of the enzymes that are involved in the synthesis (encoded by _EEB1_ and _EHT1_) and hydrolysis of the MCFA ethyl esters (encoded by _EHT1_). [PERSON] et al. found that the maximum expression level of _EEB1_ is correlated with ethyl hexanoate concentration, but not ethyl octanoate and decanoate [29]. Due to Eht1 possessing both synthesis and hydrolysis activity towards ethyl esters, there is a strong negative correlation between _EHT1_ expression levels and the end concentrations of ethyl octanoate and decanoate [29]. In this study, we found that _EEB1_ was repressed in UFAs added fermentation, and _EHT1_ were simultaneously up-regulated, which might explain the pronounced reduction of ethyl ester in UFAs addition fermentation as compared to the control (Figure 5). Some authors believed that precursor concentrations (MCFA) are the limiting factor for ethyl ester synthesis, because the addition of MCFA to the fermentation medium resulted in higher ethyl ester production [28]. We did not observe the corresponding relationship between MCFAs and ethyl esters in OA_12 and LA_12 wine, although high MCFAs were produced in both wines (Figure 3). Conversely, there was a great reduction of ethyl esters contents, which was in line with the down-regulation of _EEB1_ and up-regulation of _EHT1_ (Figure 5).