Metabolomic and Transcriptomic Analysis Reveal the Impact of Delayed Harvest on the Aroma Profile of ‘Shine Muscat’ Grapes

Delayed harvesting of grapes can alter fruit quality and plays an important role in alleviating the problem of market saturation during peak seasons, as well as in regulating the supply period of grapes. In this study, by conducting a comparative analysis of fruit quality, metabolomics (aroma compounds) and transcriptome sequencing of ‘Shine Muscat’ grapes harvested at six different on-tree ripening stages after maturity, we found that: (1) delayed harvesting led to dramatic variation in berry color change (light green to yellow) with a significant increase in soluble solids (19.5 to 20.89 Brix); (2) A total of 25 volatile aroma compounds was identified in collected berry samples, while trans-2-hexenal and hexanal exhibited the highest concentrations in all samples, marking them as key volatile compounds in ‘Shine Muscat’ grapes. Notable variation in the concentrations of linalool, n-butanol, benzyl alcohol, phenylethanol, β-citronellol, and propionic anhydride were recorded in selected harvest periods. OAV analysis results show that linalool has the largest OAV among the detected compounds, and its OAV proportion increased from 53% to 95% during the six sampling periods of ‘Shine Muscat’; (3) Transcriptome sequencing of selected samples demonstrated a positive correlation between eight terpene-synthesis-related genes and linalool accumulation. Furthermore, genes within the MEP pathway (specifically VvTPS55, VvTPS59) and several transcription factors were associated with terpenoids metabolism. Based on soluble solids and OAV results, T18–T22 period (18–22 weeks post-flowering) can become good quality on-vine storge berries. The gene expression profile and developmental patterns of metabolites in MEP pathway may helpful in functional characterization of candidate genes related to terpenoid metabolism in future studies.