## 3 Results and Discussion
### PLS-Based Correlation Analysis between Fungal and Volatile Compounds  
To further investigate whether the generation of certain volatile compounds was mediated by one or more fungal communities, the PLS method was used to analyze the correlation between fungal community succession and volatile compound changes during fermentation. The fungal genera and volatile compounds were defined as variables X and Y in the PLS model, respectively. There were 10 variables (X) and 45 variables (Y) analyzed.  
The two large circles in the center and the outermost part of the Figure 6 represented the 50% and 100% confidence intervals, respectively, and variables located between the two circles indicated that they could be well explained by the model. It could be seen from Figure 6 that all of the volatile compounds were located within the 50% to 100% confidence interval, indicating that the model had good explanatory power between the  
Figure 5: (**a**) Score plot of volatile compounds in Laobaign _Baijiu_ using HS-SPEM-GC\(-\)MS analysis; (**b**) Loading plot of volatile compounds in Laobaign _Baijiu_ using HS-SPEM-GC\(-\)MS during the PCA analysis.  
variables. Candida had the highest correlation with 8 of the main volatile compounds and had positive correlation coefficients with ethyl isobutyrate (13), ethyl butanoate (14), ethyl isovalerate (15), isoamyl acetate (16), ethyl valerate (17), ethyl hexanoate (18), ethyl lactate (19), and ethyl heptanoate (20). Pichia was well correlated with 5 of the main volatile compounds and had positive correlation coefficients with ethanol (1), 3-methylbutanol (4), ethyl phenylacetate (26), acrolein (30), and hexanal (31). Trametes was correlated well with 5 of the main volatile compounds and had a positive correlation with ethanol (1), 3-methylbutanol (4), acrolein (30), acetophenone (37), and octanoic acid (40); Saccharomyces genera correlated strongly with pentanol (5) and ethyl caprylate (21). Wickerhamomyces was better correlated with 2,3-butanedione (34). _Mucor_ was better correlated with ethyl tetradecanoate (27), 2-methylpropionaldehyde (29), 2,3-butanedione (34), and furfurral (42). Aspergillus and Penicillium were better correlated with dimethyl trisulfide (45). Rhizous was strongly correlated with acetophenone (37) and octanoic acid (40).  
It showed that the position of the most volatile compounds was well correlated with the position of Saccharomyces, Pichia, Candida, Trametes, and Rhizous. It is the most relevant for interpreting the formation of volatile compounds. Especially for Pichia and Candida, the position of the most volatile compounds distributed around them indicated that these two genera were the two most important contributors to the formation of flavors during _Baijiu_ fermentation. In addition, Aspergillus, Penicillium, Wickerhamomyces, and Mucor showed a good correlation with certain volatile compounds but showed a poor correlation with the most volatile compounds. The position of Torulaspora was far from all of the volatile compounds on the loading plot (Figure 5b), which indicated that Torulaspora is not the core genera that produces volatile compounds, which was in line with the previous study [4].