Monoterpenes are synthesized in the plant from five-carbon isoprene units and are recognized for their citrus, floral, and earthy aromas. Variations in terpene profiles in Vitis vinifera winemaking grapes are largely attributed to the genetic diversity of the species. However, nonterpenic and terpenic varieties possess the same number of terpene synthase genes. Glycosylation presents one avenue of terpene metabolism that could explain differences in terpene concentration among cultivars of Vitis vinifera. Glycosidically bound monoterpenes are nonvolatile and can be stored in the plant. When the plant tissue is disrupted, hydrolysis of the glycoside precursors by acidic conditions or enzyme catalysis can yield an aroma active terpene, making monoterpene glycosides a reservoir of potential aroma. While terpene biosynthesis has been studied in several plant species, little is known about the biosynthesis of monoterpene glycosides in grapes. Using a previously developed UHPLC/QTOF-MS method for tentative identification and profiling of monoterpene glycosides, an expanded database of twenty-eight monoterpene glycosides including an additional ten compounds was constructed. A targeted approach using this database was applied to investigate changes in glycoside profiles in Muscat of Alexandria, Muscat of Hamburg, Riesling, Pinot Noir, Chardonnay, and Cabernet Sauvignon varieties during grape berry maturation. The variation in monoterpene profiles was then linked to underlying genetic relationships among cultivars. Not all glycosides were observed in each varietal but trends in glycoside profiles during berry maturation were similar for closely related Muscat of Alexandria and Muscat of Hamburg varieties. The ten additional glycosides, representing three different classes of monoterpene glycosides, were observed in multiple varieties. These were tentatively identified based on characteristic MS/MS fragmentation patterns and comparison to previous reports. This workflow is also being adapted to monitor monoterpene glycoside profiles throughout winemaking, giving insight to the effect of winemaking practices on aroma precursors that can influence aroma of finished wine.

Changes in monoterpene glycosylation patterns in Vitis vinifera during grape berry maturation

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.