# Difference in Aroma Components of Black Teas Processed on Different Dates in the Spring Season
## 3 Results and Discussion
### Screening of the Key Differential Odorants Based on OAV  
The contributions of individual volatile compounds to the overall aroma are closely related to their OT in addition to their concentrations. Volatile compounds with low concentrations frequently make a larger contribution to the tea aroma than those with high concentrations [40]. Compared with the concentration, the OAV provides a more reasonable evaluation of individual aroma components' contributions to the overall flavor. Thus, it has been extensively applied in flavor research. As shown in Table 3, the OAVs of 25 aroma compounds were greater than 1 in at least one black tea. The total OAV of odorants was gradually increased from 1762.1 (ZYQ-1) to 2252.5 (ZYQ-4), and then slightly decreased to 2055.1 (ZYQ-5), which was consistent with the changes in the content of volatile compounds (Figure 1). The predominant odorants were \(\beta\)-ionnone, \(\beta\)-damascenone, linalool, (E)-\(\beta\)-ocimene, and geraniol, all larger than 100. Owing to their high OAVs, they were considered as the key aroma-active compounds in ZYQ black teas. \(\beta\)-Ionone, \(\beta\)-damascenone, linalool, and geraniol have been previously identified as important aromatic compounds in black teas [8; 10; 11; 13; 41], while (E)-\(\beta\)-ocimene was first identified as an important aroma-active compound for black teas. In addition, (E,E)-2,4-nonadienal, cis-3-hexenyl isovalerate, and (E)-2-nonenal showed moderate OAVs. The OAVs of naphthalene, ocinene, \(\beta\)-cadinene, cis-linalool oxide (furanoid), trans-linalool oxide (furanoid), 3-methylbutanal, 2-methylbutanal, and benzene acetaldehyde, etc., were lower than 10; thus, these odorants may have comparatively smaller contributions to the aroma of ZYQ black teas. Figure 4: Heat-map of the levels of differential volatile compounds. The data were UV-scaled and clustered according to Pearson correlation coefficients. With the exception of \(\beta\)-damascenone, \(\beta\)-ionnone, and cis-3-hexenyl isovalerate, the other 22 odorants showed significant differences in their concentrations (Table 2). As linalool, (E)-\(\beta\)-ocimene, geraniol, and (E,E)-24-nonadien showed much higher OAVs compared with other differential odorants, they were deemed the key differential odorants affecting the aroma quality of the black teas produced on different dates in the spring season. Linalool, (E)-\(\beta\)-ocimene, and geraniol are VTs (Table 1) and pleasant odorants emitting floral, sweet, and warm scents [7; 32; 33]. It is worth noting that the OAVs of linalool, (E)-\(\beta\)-ocimene, and \(\beta\)-damascenone reached the maximum in ZYQ-4, which supported the notion that ZYQ-4 presented a slight floral aroma (Table 1). (E,E)-24-nonadien is an FADV emitting a cucumber-like scent [8]. In addition, (E)-2-nonenal, 3-methylbutanal, and nonanal showed moderate OAVs and thus were considered to have a considerable impact on the difference in aroma quality. Other odorants, such as colimene, \(\delta\)-cadinene, cis-linalool oxide (furanoid), and meridolol, imposed a smaller influence. According to the aroma characteristics, these odorants can be divided into two classes: Class I odorants mainly emit unpleasant scents, such as green, grassy, or pungent odors; Class II odorants mainly emit pleasant scents, such as floral, fruity, or sweet odors. The Class I odorants consisted of naphthalene, hexanal, (E)-2-octanal, nonanal, (E)-2-nonenal, (E,E)-2,4-nonadienal, and methyl salicate; and the Class II odorants included \(\beta\)-ionnone, \(\beta\)-damascenone, linalool, (E)-\(\beta\)-ocimene, geraniol, cis-3-hexenyl isovalerate, 3-methylbutanal, and benzene acetaldehyde, etc. The total OAV of Class I odorants gradually decreased from 145.1 (ZYQ-1) to 70.4 (ZYQ-4) and then increased to 101.1 (ZYQ-5), while the total OAV of Class II odorants showed an inverse change trend. In addition, the ratio of Group II/Group I OAVs was in line with the change in the total OAV of Class II odorants (Table 3).