Abstract
In grape berries (Vitis vinifera L.), sesquiterpenes are mainly accumulated as hydrocarbons in the epicuticular wax layer of grapes, whereas monoterpenes, which are predominantly present as alcohols, are glycosylated and are stored as glycosides in the vacuoles of grape berry cells. In this study, extensive analysis of grape berry hydrolysates by means of comprehensive two-dimensional gas chromatography–time-of-flight–mass spectrometry demonstrated that glycosylated sesquiterpene alcohols show very little structural diversity when compared to the sesquiterpene hydrocarbon fraction in the cuticle and are glycosylated to a rather low extent when compared to monoterpenols. Twenty-four enzymatically released terpenols were found in hydrolysates of the aromatic white wine variety Gewürztraminer (V. vinifera subsp. vinifera) after previous solid-phase extraction and headspace solid-phase microextraction. The detection of only three sesquiterpene alcohols, namely farnesol, nerolidol and drimenol, shows that most sesquiterpene hydrocarbons do not have a related hydroxylated structure in grapes. Nevertheless, the presence of the acyclic aglycone farnesol and nerolidol may be of importance for the wine aroma, since these structural isomers can be converted into numerous sesquiterpenes by nonenzymatic acid-catalyzed reactions during wine production. Grape-derived glycosidically bound sesquiterpene alcohols, therefore, represent, in addition to free sesquiterpene hydrocarbons, another pool of compounds that may influence the aroma profile of wines.
Highlights
Terpenes play a key role as plant secondary metabolites for the aroma of grapes (Vitis vinifera L.) and wines [1]
The hydrolysates were analyzed by comprehensive two-dimensional gas chromatography–time-of-flight–mass spectrometry (GC × GC–TOF–MS) after previous headspace solid-phase microextraction (HS-SPME)
The terpene alcohols were extracted from headspace using a mixed SPME fiber for volatile and semivolatile compounds (C3–C20) from Supelco (Bellefonte, PA, USA), based on a method described by Welke et al [25]
Summary
Terpenes play a key role as plant secondary metabolites for the aroma of grapes (Vitis vinifera L.) and wines [1]. Both mono- (C10) and sesquiterpenes (C15), which are formed. While monoterpene glycosides in grapes have been extensively investigated in recent years [15,16,17,18], glycosidically bound sesquiterpenes in V. vinifera are still largely unknown. Since glycosidically bound terpene alcohols are partly released both enzymatically and acid catalytically during winemaking [20, 21], grape-derived sesquiterpene glycosides represent an unexplored aroma potential, in addition to monoterpene glycosides. The glycosidically bound terpenes from isolated exocarp of grapes were separated and concentrated using solid-phase extraction (SPE) and subsequently hydrolyzed enzymatically. The hydrolysates were analyzed by comprehensive two-dimensional gas chromatography–time-of-flight–mass spectrometry (GC × GC–TOF–MS) after previous headspace solid-phase microextraction (HS-SPME)
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