Evolution of grapeseed composition during maturation and characterization of its impact on wine compound using molecular networks

Abstract

Usually the winemaker consider the grapeberry maturity as an actor of the wine quality. Grape seed are frequently used as a marker to assess the grape maturity. The first aim of this study is to obtain a better understanding of the impact of grape seed maturity on the grape seed and grape berry composition. Furthermore, due to the lack of knowledge regarding grape seeds and the need for new maturity markers, part of this work aims to enhance the current methods of assessing grape seed maturity to help winegrowers determine the best harvest time. A second goal of this study is to characterize the effect of grape seed maturity on wine and to identify new compound in wine derived from grape seed.

Data for this study were collected from grape seeds picked at different maturity stages (from bunch closure to 2 weeks after harvest) and wines made at three harvest time (underripe, ripe and overripe) in 2024. Each grape seed sample was frozen until analysis and then samples were ground and extracted during 24H in methanol. They were then filtered and dried. The wine samples were directly filtered and dried without any prior extraction. Then they were diluted to the same concentration (1 mg/mL) and analyzed by HPLC MS/MS. All the results were used to construct a molecular network using the fragmentation pattern and retention time of the molecules¹. The different results were analyzed using the software MetGem². MetGem or personal annotation were used to annotate the molecules in the molecular network that were not found in the database but still appeared promising. With the grouping capability of molecular networks, families of molecules were identified (polyphenol, AA, nitrogen compounds). Even in the well-known family of molecules (polyphenols), recently discovered molecule (epicatechin vanillate³) and potential new molecules were annotated. Not all molecule can be classified into family through molecular networking. Even so, molecules might be studied using semi (SQ) and quantitative approaches to validate markers of ripening evolution in grape seeds and to confirm their involvement in grapeberry ripening evaluation as well as in winemaking processes. For example, amino acid found in grapeseed could contribute to wine aroma⁴. Additionally, the quantity of catechin glucoside (found in red wine⁵) appear to increase (SQ approach) in grape seed during maturity, potentially being a good grape seed maturity marker. Finally, this work has enabled us to combine the molecular network approach and a semi-quantitative method to deepen our knowledge of grape seed ripening driven by specific markers.

References

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