First disclosure of eugenol precursors in Vitis genus: analytical development and quantification

Abstract

The main aim of this work was to develop an analytical method to disclosure the molecular form of eugenol precursor. Indeed eugenol is an important contributor to Armagnac spirits typicity made with Baco blanc. Moreover the high content of eugenol found in Baco blanc may be one of the reasons why this variety is tolerant, thereby requiring fewer phytosanitary treatments overall compared with Ugni blanc or Folle blanche. Prior to our work, the eugenol potential was estimated after enzymatic release using unspecific glycosidase enzyme preparations. However, the chemical structure of the actual eugenol glycoconjugates precursors had never been fully elucidated. To reveal the identity of eugenol precursors, an innovative specific methodology was developed and applied to berry skin extracts. This EPIQ strategy (Extraction-Purification-Identification-Quantification), involved HS–SPME, GC–MSguided LC fractionation, use of specific enzymatic hydrolyses, as well as LC–MS/MS and LC–HRMS analyses. We identified geoside (eugenyl-6-O-α-L-arabinopyranosylb-D-glucopyranoside) as the major eugenol precursor, and confirmed this identification with commercially available standards. To the best of our knowledge, this is the first study to identify geoside in grapevine. Additionally, three minor eugenol precursors were detected, including the monoglucoside citrusin C (eugenyl b-Dglucopyranoside).

An LC-MS/MS (MRM) quantification method was then established and validated based on linearity, inter-day and intra-day precision. LC–MS/MS quantifications confirmed that geoside is present in greater amount in Baco blanc than in Vitis vinifera grape varieties such as Ugni blanc, Folle blanche and Plant de Graisse. Moreover, we studied the synthesis of geoside during fruit development and found that in Baco blanc, geoside reached its highest concentration in berry skins at veraison. Finally these quantifications performed on various Vitis species and their hybrids demonstrated that geoside is specific to certain grapevine hybrids, particularly Baco blanc.

The strategy developed in this study could be easily applied for the exploration of other aroma precursors in different grape compartments and varieties.

References

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