# Dynamics of Microbial Community Structure and Metabolites during Mulberry Ripening
## 3 Results and Discussion
### Dynamic Changes in Volatile Flavour Compounds in WHDS during Ripening  
The aroma composition of mulberry is complex and mainly derived from the metabolic decomposition of fatty acids, amino acids, and other precursors, the type and content of which will be affected by the variety, maturity, and growth environment [51]. As can be seen in Table 3, a total of 26 volatile flavour substances were detected during the maturation process of WHDS, including eight esters, seven alcohols, four acids, three aldehydes, two ketones, and one each of phenols and terpenes. The total content of volatile flavour substances increased with the maturation degree and basically reached a stable level at S4, with the total content in the range of 209.09 \(\pm\) 4.92 mg/L to 1279.09 \(\pm\) 33.50 mg/L. Alcohols, at 59-69%, are the main source of WHDS aroma, mainly 2,3-butanediol, 3-Methyl-1-butanol, and 1,2,3-Propanetriol. These higher alcohols not only act as precursors to esters, but also give WHDS a rosy, herbaceous, and oily bark flavour to increase the body [52; 53]. The largest variety of esters, most of which are derived from esterification reactions, contribute significantly to flavour formation in WHDS. Ethyl butyrate, ethyl benzoate, and methyl caproate are the more common volatiles of the five stages, which can give WHDS a more pineapple and grassy aroma, and the ethyl caproate and ethyl propionate generated in S4 and S5 can increase its sweetness and fruity taste [54]. Ethyl propionate and ethyl valerate were only detected in the pre-ripening stage. Acids, which are also precursors of esters [55], are the main constituents of the mulberry aroma. The content of acetic and butyric acids increased with maturity, with lactic and acetic acids gradually appearing in the later stages of ripening. Aldehydes and ketones are fewer in variety and lower in content, but they are also an important part of the mulberry aroma. Amino acids are an important source of aldehydes [56], and high concentrations of alcohols also increase aldehydes under aerobic conditions [57]. The detected compounds isovaleraldehyde, furfural, phenylacetaldehyde, and 3-hydroxydibutanone reduce oral and oesophageal irritation [58] and enhance the softness of the WHDS taste. Terpenediene and phenol also optimise the aroma and flavour of WHDS. In addition, we performed PCA and categorised the flavour substances for the five stages, and the results are shown in Figure 5. As shown in Figure 5a, the total explanation of the two principal components is 88.0%, and, according to the division of RDA1 and RDA2, S1 and S2 are in the third quadrant, S3 is in the second quadrant, S4 is in the fourth quadrant, and S5 is in the first quadrant, with no overlap among any of the stages, which suggests that there is a high degree of variability among the five maturity stages. In terms of the area covered, the S4 stage was the most extensive, indicating the greatest variety of flavour substances at 22, which is in keeping with the findings shown in Figure 5b. Studies have shown that there are significant differences in the flavour substances of WHDS at different ripening stages, and the scientific and rational harvesting of fruits at different stages can ensure the edible quality and nutritional value of WHDS and is conducive to further processing. Figure 4: Radar map display of the K (**a**), Ca (**b**), Fe (**c**), and Se (**d**) in WHDS at different maturity stages. Figure 5: Principal component analysis (PCA) (**a**) and Sankey diagram (**b**) of volatile components at different maturity stages of WHDS.