## 2 Results
### Differential Accumulation Metabolites of Volatile Organic Compounds Analysis of C. oleifera Petals
#### 2.3.2. Crucial Differential VOCs Related to _C. Oleifera_ Petals Aroma  
As shown in Figure 4, the phenylethyl alcohol, lilac alcohol, 2-propenal,3-(2-furanyl)-, and butanoic acid, 1-methylhexyl ester were only detected in W petals, and displayed a higher accumulation level. 4-hexen-3-one and 2-hexenal were found only in CP petals with a higher level. Isobornyl formate, and hotrienol were present at a higher level in DR petals. In the W_vs_CP comparison, most VOCs-DAMs were terpenodisthe. The top five up-regulated VOCs with higher content in CP petals were Butanoic acid, 3-hexenyl ester, (E)- (S)- (4.15-fold), 7-Octen-4-ol, 2-methyl-6-methylene-, (S)- (4.08-fold), (E)-2-6-Dimethylocta-5,7-dien-2-ol (3.54-fold), cyclohexene, 1-methyl-4-(1-methylylidene)- (2.73-fold), and hotrienol (2.02-fold). Lilac aldehyde (0.132-fold), tetradecane (0.131-fold), isopinocarveol (0.106-fold), gamma-terpinene (0.059-fold), and undecane, 3,5-dimethyl- (0.007-fold) were significantly down-regulated from W petal to CP petal. In the W_vs_DR comparison, the higher concentrations in the DR petals were furan, 3-(4-methyl-3-pentenyl)-, hotrienol, 2-isopropyl-5-methylhex-2-enal, 1-Nonen-4-ol, Cyclohexene, 1-methyl-4-(1-methylylidene)-, 3-hexen-1-ol, propanoate, (Z)-, and butanoic acid, 2-methyl-, 2-methylbutyl ester, which were up-regulated by 2.05-, 2.20-, 2.58-, 2.38-, 2.35-, 2.68-, and 11.49-fold, respectively. Undecane, 3,5-dimethyl-, gamma-terpinene, and (3R,6R)-2,6-trimethyl-6-vinyltetrahydro-2H-pyran-3-ol were up-regulated by 0.009-, 0.058-, and 0.082-fold, respectively.  
Figure 3: Venn diagram and pathway analysis of VOCs-DAMs in three _C. Oleifera_ petals. (**A**): The Venn diagram results among W_vs_CP, W_vs_DR, and CP_vs_DR comparisons. (**B–D**): KEGG pathway enrichment of the VOCs-DAMs of the W_vs_CP, W_vs_DR, and CP_vs_DR comparison, respectively. W = white petals; CP = candy-pink petal; DR = dark-red petal.  
In the CP_vs_DR comparison, it was found that butanoic acid, 2-methyl-, 2-methylbutyl ester, 2,4-Octadienal, (E,E)-, and 1H-Imidazole, 2-propyl- displayed a high accumulation level in the DR petals, which were up-regulated by 5.28-, 2.26- and 2.99-fold, respectively. 7-Octen-4-ol, 2-methyl-6-methylene-, (S)- and alpha-terpineol were down-regulated by 0.269- and 0.341-fold, respectively.  
Overall, the contents of phenylethyl alcohol, linac alcohol, and butanoic acid, 1-methylhexyl ester with rose, fruity, and honey aroma attributes in white _C. oleifera_ petals were significantly higher than those in candy-pink and dark-red petals, which might make the white petals richer in aroma. The hotrienol, alpha-terpineol and 7-Octen-4-ol, 2-methyl-6-methylene-, (S)- with sweet and delicate fragrance flavor exhibited a higher accumulation level in candy-pink _C. oleifera_ petals. The hotrienol, butanoic acid, 2-methyl-, 2-methylbutyl ester, and 2,4-Octadienal, (E,E)- with wood and fruity flavor were the primary VOCs in the dark-red _C. oleifera_ petals.  
Figure 4: Violin plots of peak areas values of 12 crucial differential VOCs identified in W, CP, and DR petals. W = white petals; CP = candy-pink petal; DR = dark-red petal. The distribution and probability density of the 12 VOCs-DAMs were represented by a combination of box plots and density plots. The outer shapes represented the density of the peak area values distribution, the black rectangular box in the middle represents the quartile range, and the white circle in the middle represents the median.