## 4 Conclusions  
Both free and glycosidically bound forms of volatile compounds in Vidal grapes from the Shangri-La high-altitude region during the on-vine non-destructive dehydration process were investigated in this study. After two months of on-vine dehydration, the sugar content and acidity of the grape juice were dramatically enhanced, while the berry weight and juice yield sharply decreased. Predominantly in the bound forms, FADs, AADs, and IPDs were the three main types of volatiles in dehydrated Vidal grapes. Although water-loss concentration played a considerable role during non-destructive dehydration, biosynthesis and biodegradation also occurred during this process, eventually modifying some volatiles significantly, especially for some powerful odorants such as hexanal, _trans_-2-hexenal, 2-phenethyl acetate, \(\beta\)-myrcene, linalool, geraniol, _cis_-rose oxide, and \(\beta\)-damascenone. The evolution pattern of the volatile compounds in on-vine non-destructive dehydration differed from that in destructive dehydration or post-harvest dehydration processes, as anaerobic metabolism of the grape berries did not occur during on-vine non-destructive dehydration in our study. The U-LRA results indicated that 1-octen-3-ol was relatively stable during the non-destructive on-vine dehydration process and its content in grape juice was mainly determined by the concentration effect. Twenty-seven free-form compounds with VIP values greater than 1.0 were screened by OPLS-DA as metabolic markers to discriminate the grapes at different dehydration degrees, among which 2,4-di-_tert_-butylphenol, 2-phenethyl acetate, 2-methyl-1-propanol, and hexanol, with VIP values above 2.0, were the most important metabolic markers. Our study also highlights the fundamental importance of the expression of volatile content in the metabolomic study of grape berries.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/horticulturalrea8111029/s1](https://www.mdpi.com/article/10.3390/horticulturalrea8111029/s1)]([https://www.mdpi.com/article/10.3390/horticulturalrea8111029/s1](https://www.mdpi.com/article/10.3390/horticulturalrea8111029/s1)), Figure S1: Meteorological data during the sampling period of the vineyard; Figure S2: Visual appearance of the grapes after harvest at T5; Figure S3: PCA score scatter-plots of free (a) and bound (b) forms of volatiles, expressed as ng per berry; Figure S4: Permutation plots of samples at different dehydration degrees (T1, T2, T3, T4, and T5); Table S1: Volatile compounds detected in Vidal grapes grown in Weixi at different on-vine dehydration degrees expressed by ng/L; Table S2: Volatile compounds detected in Vidal grapes grown in Weixi at different on-vine dehydration degrees, expressed by ng/berry.  
Conceptualization, Q.-F.X. and L.F.; methodology, Q.-F.X. and L.F.; investigation, K.-X.L.; resources, M.-X.Z.; software, D.-M.Z.; writing--original draft preparation, Q.-F.X.; writing--review and editing, L.F. and J.C.; supervision, M.-X.Z.; funding acquisition, J.C. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the Special Basic Cooperative Research Programs of Yunnan Provincial Undergraduate Universities' Association (grant NO. 2018 FH001-040).  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.  
**Acknowledgments:** All the authors thank Yunnan Zangdi Tianxiang Winery for supporting the grape sampling.  
**Conflicts of Interest:** The authors declare no conflict of interest.