## 3 Results
### Expression Analysis of Key Metabolites Affecting Aroma Formation  
In order to identify key metabolites affecting aroma formation at the maturation stage of these three grape cultivars, we conducted a KEGG enrichment analysis for the comparison of the groups J2 vs. A2, J2 vs. M2, and A2 vs. M2. \"Biosynthesis of secondary metabolites\", \"Monoterpenoid biosynthesis\", \"Limonene and pinene degradation\", and \"Metabolic pathways\" were all discovered in the comparison of the groups J2 vs. A2 and J2 vs. M2. Besides these four KEGG pathways, \"Tropane, piperidine and pyridine alkaloid biosynthesis\" and \"Phenylalanine metabolism\" were discovered in the comparison of the groups A2 vs. M2 (Figure 2a-c, Table S6). In total, 14 metabolites were significantly enriched in these pathways, of which 10 were significantly enriched in the comparison of J2 vs. A2; 9 were significantly enriched in the comparison of J2 vs. M2; and 12 were significantly enriched in the comparison of A2 vs. M2 (Figure 3a, Table S6).  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**Class** & \multicolumn{3}{c}{**A2 vs. A1**} & \multicolumn{3}{c}{**J2 vs. J1**} & \multicolumn{3}{c}{**M2 vs. M1**} \\ \hline  & **No.** & **Up** & **Down** & **No.** & **Up** & **Down** & **No.** & **Up** & **Down** \\ \hline Acids & 1 & 0 & 1 & 2 & 1 & 1 & 1 & 1 & 0 \\ Alcohols & 7 & 7 & 0 & 6 & 5 & 1 & 6 & 6 & 0 \\ Aldehydes & 5 & 5 & 0 & 2 & 2 & 0 & 3 & 3 & 0 \\ Amines & 1 & 1 & 0 & 1 & 1 & 0 & 1 & 1 & 0 \\ Aromatics & 3 & 3 & 0 & 6 & 2 & 4 & 3 & 1 & 2 \\ Esters & 9 & 7 & 2 & 6 & 4 & 2 & 12 & 8 & 4 \\ Heterocyclic compounds & 17 & 16 & 1 & 6 & 3 & 3 & 8 & 5 & 2 \\ Hydrocarbons & 8 & 7 & 1 & 5 & 3 & 2 & 3 & 2 & 1 \\ Ketones & 6 & 6 & 0 & 4 & 3 & 1 & 3 & 3 & 1 \\ Nitrogen compounds & 2 & 2 & 0 & 0 & 0 & 0 & 0 & 0 & 0 \\ Terpenoids & 34 & 33 & 1 & 14 & 8 & 6 & 12 & 11 & 1 \\ Other & 1 & 0 & 1 & 1 & 0 & 1 & 1 & 0 & 1 \\ \hline \end{tabular}
\end{table}
Table 1: Dynamic change in aromatic compounds in three cultivars at different development stages.  
Figure 1: KEGG enrichment analysis of different accumulated metabolites for these three cultivars at different development stages. (**a**) Venn diagram for different groups. (**b–d**) Scatter plot of KEGG enrichment analysis for different development stages.  
The grape cultivar \"Adenauer Rose\" possesses a strong muscat fragrance and \"Ky-oho\" possesses a strong strawberry fragrance. To further discover the key metabolites that could significantly affect the flavor formation of these two cultivars, six metabolites were selected according to the KEGG pathway enrichment analysis, i.e., 2,7,7-trimethyl-3-Oxatricylcolq[4.1.1.0(2,4)]octane(D197), Myrcene(KMW0199), D-Limonene(KMW0217), 4-methyl-Benzenemethanol (NMW0038), L-alpha-Terpineol(NMW0071), and 6,6-dimethyl-Bicyclolc[3.1.1]hept-2-ene-2-methanol (NMW0074) in J2 vs. A2, J2 vs. M2, and A2 vs. M2. Two metabolites, 3-Carene(KMW0220) and (1R,2S,5S)-2-methyl-5-(1-methylethyl)-Bicyclolc [3.1.0] hexan-2-ol(KMW0257), were only selected according to J2 vs. A2 and J2 vs. M2. Two metabolites, Citral (KMW0446) and Geraniol (KMW0460) were only selected according to J2 vs. A2 and A2 vs. M2. One metabolite, \(\alpha\)-Pinene (KMW0148), was only selected according to J2 vs. M2 and A2 vs. M2, and three metabolites, BenzeneacetAldehyde (KMW0212),  
Figure 3: Statistical analysis of differentially accumulated metabolites for three cultivars at their maturation stage. (**a**) Venn diagram for different groups. (**b**) Heatmap of dynamic change for all significantly accumulated metabolites at different development stages.  
Figure 2: KEGG enrichment analysis of different accumulated metabolites for three cultivars at their maturation stage. (**a**) KEGG enrichment analysis of the groups J2 vs. A2, (**b**) KEGG enrichment analysis of the groups J2 vs. M2. (**c**) KEGG enrichment analysis of the groups A2 vs. M2.  
(-)-trans-Isopiperitenol (NMW0082), and 2,3,4,5-tetrahydroo-Pyridine(XMW0132), were only selected according to A2 vs. M2 (Figure 3b, Table S6).