## 5 Conclusions  
In conclusion, the aroma profile and characteristic odorants in the main current commercial citrus blend black teas were thoroughly investigated utilizing HS-SPME-GC\(\times\)GC-TOFMS combined with GC-O/MS techniques for the first time. A total of 348 volatile compounds were ultimately identified that consisted of \(>\)50% alkenes and aldehydes. The PLS-DA resulted in 30 significant differential volatile compounds among the three types. Moreover, GC-O/MS analysis revealed 61 aroma-active compounds. Most of these compounds presented green, fresh, floral, lemon-like fruity, and sweet scents. Especially heptanal, limonene, linalool, and trans-\(\beta\)-ionnone were considered as the basic odorants for citrus blend black tea flavors. The combination of GC\(\times\)GC-TOFMS and GC-O/MS indicated that each group had a unique composition of volatile compounds, namely, limonene, octanoic acid ethyl ester, copaene, ethyl butyrate in CG, benzyl acetate, and nerol in BG, and furfural in LG. The combination of results reliably identified blended tea aromas and flavors and led to a comprehensive understanding of the flavor sources in citrus blend black tea. Meaningful, the result also lays the foundation for the cultivar discrimination and aroma quality control of the popular blended teas. Our subsequent studies will focus on identifying unknown odorants, improving analytical approaches, and uncovering synergistic and inhibitory effects among odorants.  
The following are available online: Figure S1: Optimization of citrus blend black tea volatile extraction (A), tea to water ratio (B), extraction temperature (C), Figure S2. The GC\(\times\)GC chromatograms of LB-MGHC aroma extracts in Citrus group, Figure S3. The GC\(\times\)GC chromatograms of CN-BJHC aroma extracts in Bergamot group, Figure S4. The GC\(\times\)GC chromatograms of LD-NMHC aroma extracts in Lemon group, Table S1: Sensory evaluation of 50 citrus blend black tea samples, Table S2: Identified volatile compounds and contents in citrus blend black teas, Table S3: The detailed performance of GC-O analysis of Citrus Group samples, Table S4: The detailed performance of GC-O analysis of Bergamot Group samples, Table S5: The detailed performance of GC-O analysis of Lemon Group samples.  
Conceptualization, Z.L., Y.Z. ([PERSON]), J.S. and J.W.; methodology, Y.Z. ([PERSON]) and J.W.; software, J.W.; validation, J.W.; formal analysis, J.W.; investigation, J.W., Y.Z. ([PERSON]), H.Y., M.W., W.M., Y.Z. ([PERSON]), J.S. and Q.P.; resources, J.W., Y.Z. ([PERSON]), H.Y., M.W., W.M., Y.Z. ([PERSON]), J.S. and Q.P.; data curation, J.W., Y.Z. ([PERSON]); writing--original draft preparation, [PERSON]; writing--review and editing, J.W., Y.Z. ([PERSON]), J.S., Z.L. and Y.C.; visualization, [PERSON]; supervision, Y.Z. ([PERSON]), J.S. and Z.L.; project administration, J.W., Y.Z. ([PERSON]); funding acquisition, Y.Z. ([PERSON]) and Z.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Natural Science Foundation of China, grant number 31701702; Special Funds for the Construction of Modern Agricultural Technology Systems, grant number CARS-19; Science and Technology Innovation Project of the Chinese Academy of Agricultural Sciences, grant number CAAS-ASTIP-2014-TRICAAS.  
The authors would like to thank the sensory and GC-O/MS panelists in Key Laboratory of Tea Biology and Resources Utilization, Ministry of Agriculture, Tea Research Institute, Chinese Academy of Agricultural Sciences.  
The authors declare no conflict of interest.