## 4 Discussion
The esterification of ethanol using certain fungi and the heterolactic fermentation of LAB, ester formation of ethyl acetate, and ethyl lactate were carried out during the fermentation [33]. This was confirmed by our results showing that the concentration of ethyl acetate was higher during fermentation (with Lbr17). Ethyl acetate contributes a fruity (pineapple) and sweet aroma, enhancing the olfactory complexity and bouquet of _Baijiu_[34]. The technique of qPCR can accurately measure the quantity of microorganisms, which has been utilized to study the physiological metabolism and microbial community distribution and applied to the quantitative study of functional bacteria in _Baijiu_ fermentation. [PERSON] et al. used qPCR to quantify the total bacteria and fungi in the fermentation process of _Fenjiu_[35]. It was found that the content of bacteria was increased while that of fungi was more stable in the fermentation process. Simultaneous investigation of bacterial and fungal variations is important in understanding food fermentation processes. As shown in Figure 4E, the fortified fermentation group displayed significantly higher levels of _L. brevis_ compared to the CK in the initial 15 days of fermentation, indicating that fortified inoculation of _L. brevis_ played a significant role during the fermentation process. Figure 4E, along with Figure 4A,C, demonstrated that the increase in _L. brevis_ in the fortified fermentation group was significantly higher than that of _Lactobacillus_. Figure 4A revealed that the total number of bacteria was lower than that in the control group after fortified inoculation of Lbr17. These findings suggest that the growth of some _Lactobacillus_ and bacteria was inhibited by mutual exclusion while the number of _L. brevis_ increased. Figure 4E combined with Figure 4B,D show that the total fungi and yeasts in the fortified fermentation group were lower than those in the control group, indicating that fortified inoculation of _L. brevis_ could also inhibit the growth of yeasts and total fungi during fermentation. Therefore, it can be concluded that fortified inoculation of _L. brevis_ can selectively modify the microbial communities in the fermentation process via mutual exclusion, thereby improving the control over the fermentation process. The combined analysis in Figure 5 indicates that fortified fermentation did not alter the overall trend of the fermentation process but instead made fine adjustments. After inoculation on the 15 th day, parameters such as pH, titratable acid, moisture content, and reducing sugar tended to stabilize, with the fortified fermentation group displaying higher acid and moisture content compared to the control group. The high acidity of the fortified fermentation group may be due to the acid production of the inoculated _L. brevis_[36]. The higher moisture content in fortified fermentation may be due to more esterification reactions in the fortified fermentation group. Comparing the changes in reducing sugar content in the fortified fermentation group and control group from 1 to 3 days, it was found that fortified inoculation had no significant effect on the formation of reducing sugar. The higher reducing sugar content in the fortified fermentation group is likely due to decreased enzyme activity, which hampers the process of reducing sugar conversion in ethanol by yeast under low pH conditions (pH stabilizes at about 3.5 after 7 days of fermentation). This reduction in efficiency affects the reducing sugar utilization by certain yeasts. Therefore, the amount of LAB inoculated or mixed with acid-resistant yeast should be properly controlled during inoculation to weaken the influence of low pH on the growth and function of yeast. This ensures that the process of ethanol production by yeast, reducing sugar and acid production by LAB, and reducing sugar and ester production by esterification remains in good dynamic balance.