Non-targeted analysis of C13-norisoprenoid aroma precursors in Riesling

Abstract

Significant wine aroma can be formed from non-volatile precursors that are linked to sugars, including but not limited to grape-derived monoterpene and C13-norisoprenoid glycosides. Most studies aiming to profile glycosidic flavour compounds in grapes and wine are performed by the analysis of hydrolytically liberated aglycones, either enzymatically or through acid hydrolysis, mainly due to a lack of analytical standards, diversity of glycosides, and their small concentrations. However, aglycone analysis alone can not reveal the full
complexity of precursors and the structural rearrangements of aglycones during and post-release, as it has been repeatedly reported for TDN and other related C13-norisporenoids that arise slowly during wine ageing.
The main objective of this study was to develop an analytical strategy to profile the potential presence of putative lead candidates and the presence of unknown precursors involved in the formation of the potent aroma compound, TDN, in Riesling wine. To uncover the structural complexity of TDN precursors, we firstly utilised a non-targeted metabolomics
approach (using HPLC with QTOF mass spectrometry) on Riesling grape grown under varied light conditions to determine potential candidates; putative TDN precursors ex wine were then further characterised by tandem mass spectrometry (HPLC-QqQ-MS/MS).
In addition to previously reported precursors, multiple glycosides were found in Riesling wine made from grapes grown under different light regimes which represent promising candidates likely to contribute to the formation of TDN. The results demonstrate that the combined HPLC-MS methods are effective for confirming and significantly expanding the
knowledge about the precursor pools involved in the formation of potential aroma compounds in wine. At the same time, this analytical strategy can help to develop a greater understanding of the environmental influences that can drive the formation of individual flavour precursors.