Advanced characterization of oxidation markers in grape seeds condensed tannins using AcquireX™ data acquisition and feature-based molecular networking

Abstract

Condensed tannins (CTs) play a crucial role in various domains, from food quality to health benefits. They significantly contribute to the sensory profiles and stability of fruit-derived beverages, such as wines and are increasingly studied for their impact on preventing chronic diseases such as cancer and neurodegenerative disorders. However, despite their importance, understanding the structural evolution of CTs, particularly their oxidation processes, remains a significant analytical challenge. To date, oxidation markers of CTs have been identified by Liquid Chromatography coupled to Mass Spectrometry (LC-MS) after chemical depolymerization1,2. However, this process is time-consuming and largely manual. Automating data processing is crucial to maximize the value of the results. In this study, to efficiently accelerate identification of oxidation markers and overcome the challenges of finely characterizing CTs and their chemical evolution, thioglycolysis was combined with advanced analytical techniques. This includes AcquireX™ deep scan, an intelligent MS/MS data acquisition strategy and Feature-Based Molecular Networking, a powerful tool for organizing and visualizing MS/MS data, which facilitates the investigation of complex chemical matrices. This combined approach was applied to grape seeds, a well-known and rich source of CTs, to identify specific oxidation markers. Our study successfully highlighted 104 oxidation markers, including 49 previously unreported. These findings rapidly highlighted connections between structurally similar markers and enabled differentiating isomers across molecular network clusters, which might be missed by traditional methods. Detailed MS/MS analyses revealed dimers and trimers, indicating linkages between extension and terminal units, or both, classified according to their oxidation levels, from 1 to 8, revealing structural rearrangements that affect the quality and the stability of products containing them. Moreover, this innovative analytical approach, applied here for the first time, offers a new framework for studying the oxidation mechanisms of CTs in complex matrices. Beyond grape seeds, this methodology is being applied in an ongoing study to investigate broader aspects of aged wine chemistry. It focuses on both the oxidative and non-oxidative evolution of condensed tannins and their interactions, such as tannin-tannin, tannin-anthocyanin and aroma-tannin interactions during the aging process.

References

1. Mouls, L., and Fulcrand, H. (2015). Identification of new oxidation markers of grape-condensed tannins by UPLC–MS analysis after chemical depolymerization. Tetrahedron 71, 3012–3019. https://doi.org/10.1016/j.tet.2015.01.038
2. Suc, L., Rigou, P., and Mouls, L. (2021). Detection and identification of oxidation markers of the reaction of grape tannins with volatile thiols commonly found in wine. J. Agric. Food Chem. 69, 3199–3208. https://doi.org/10.1021/acs.jafc.0c07163