## 3 Results and Discussion
### Characterization of Volatile Compounds of FAA Tea in Four Harvest Times
#### 3.4.3 Key Flavor Characteristics of FAA Tea  
At present, the relative odor activity value (ROAV) is commonly used to evaluate the contribution of volatile compounds to the overall flavor. When the ROAV of a compound is >1, it is considered a key flavor compound. Figure 7d illustrates the variation in flavor compound contributions among FAA tea samples from different harvest periods. In  
Figure 7: (**a**) Metabolite count of four FAA tea samples; (**b**) Venn chart of group material overlap numbers; (**c**) accumulation diagram of relative content of species; (**d**) scatter plot of ROAV relative odor activity value; (**e**) radar map for analysis of sensory flavor characteristics. (The outermost name represents the sensory flavor characteristics, and the broken line represents the frequency grade of the corresponding flavor compound [the detection frequency is graded from 1–5, the highest frequency is grade 5], and the color indicates different groups.) this study, 36 volatile compounds with ROAV > 1 in FAA tea were identified across all samples (Supplementary Materials: Table S2). FAA-6 had the highest number of key flavor compounds (34), while FAA-3 contained the least (20). A total of 18 volatile compounds with ROAV > 1 were identified in FAA-3, FAA-4, FAA-5, and FAA-6. Among these, 12 compounds exhibited their highest ROAVs in FAA-6, ranging from 2 to 43 times the levels observed in other harvest periods. Additionally, 13 unique compounds with ROAV > 1 were exclusive to FAA-6, indicating its richer aromatic composition. The compound with the highest ROAV among all FAA tea samples was 1-octen-3-one, followed by (E)-2-octenal, isovaleric acid, (E)-2-undecenal, heptanal, and (E)-2-nonenal. The 1-octen-3-one with the highest ROAV has strong soil, mushroom, and metallic aromas with vegetable notes, like cabbage and cauliflower, and (E)-2-octenal with the second highest ROAV has fat and meat notes, as well as cucumber and chicken-like notes. Isovaleric acid and heptanal give off a sweet and fruity aroma, as well as a Duke's linguonberry-like flavor. (E)-2-Undecenal has a strong fresh aldehyde odor. And (E)-2-nonenal has a sweet or cucumber flavor [47]. The flavor of a product consists of recognizable taste and smell properties, and a complex of properties cannot be identified separately. FlavorDB was used to analyze and compare the sensory flavors of compounds [48]. As shown in the Figure 7e radar map for the sensory flavor characteristic analysis, a sweet aroma among the characteristic aromas of the four FAA tea samples was the most prominent in all of them, followed by a green aroma and fruity aroma. The FAA tea from different harvest periods differed in other aromas, except for no significant difference in the bitter aroma. The woody, floral, and clean aroma of FAA-3 was more prominent, while the sweet, green, fruity, herbal, and waxy aroma of FAA-6 was more prominent, but the waxy and medicinal aroma of FAA-4 was the weakest, and the sweet, herbal, fruity, and floral aroma of FAA-5 was weaker. A principal component analysis (PCA) of FAA tea samples from different harvest periods is shown in Figure 8a, where PC1 explained 29% of the total variance, while PC2 explained 17.2% of the total variance, with a combined contribution of 46.2%. The proximity between the three replicates in each group indicates the reliability of the results. The four sample groups were clearly separated, suggesting that the volatile principal components of the FAA tea samples differed among the different harvest periods. FAA-3, FAA-4, and FAA-5 were clustered on one side, far away from FAA-6, suggesting that the volatile components of FAA-6 differed most from those of the other three FAA tea harvest periods. In order to better compare the differences in FAA tea aromas among different harvest periods, the OPLS-DA model was established based on the relative contents of volatile compounds of FAA tea species.