Characterization of oenological tannins rich in gallotannins by multimodal mass spectrometry

Abstract

Oenological tannins are widely used in winemaking to stabilize wine color, improve must and wine clarification, prevent protein haze formation, and enhance antioxidant protection. They are extracted from different botanical sources, and comprise condensed tannins or hydrolysable tannins. Gallotannins, extracted from gallnuts, are a class of hydrolysable tannins composed of gallic acid units esterified to a polyol core, most commonly glucose. They exhibit high structural diversity, with varying degrees of polymerization. Previous studies based on nuclear magnetic resonance and liquid chromatography–mass spectrometry (LC-MS) have highlighted significant compositional variability among commercial gallotannin extracts. However, their chemical composition remains insufficiently characterized due to their high structural complexity, including extensive isomerism. The aim of this study was to improve the characterization of gallotannin-rich oenological extracts using complementary, untargeted, multimodal MS approaches. Analyses were performed on gallotannin extracts from our internal collection using two high-resolution mass spectrometers (Orbitrap Exploris 480 and timsTOF Pro2), providing orthogonal and complementary information. Three analytical strategies were combined: (1) Kendrick mass defect (KMD) analysis to visualize homologous galloyl series, (2) ion mobility spectrometry (IMS) to resolve and characterize isomeric species, and (3) molecular networking (MN) to explore structural relationships among detected compounds. These approaches enabled the establishment of a comprehensive chemical fingerprint of gallotannin extracts, revealing a high level of molecular complexity. Several previously unreported compounds and isomeric forms were detected and partially characterized, with molecular weights ranging from approximately 330 to 3000 Da. This study also revealed chemical differences and diversity among the samples, demonstrating the strong potential of multidimensional MS for the in-depth analysis of complex polyphenolic mixtures. This multimodal MS approach can be useful for the selection of oenological gallotannin extracts.

References

Watrelot, A. A.; Le Guernevé, C.; Hallé, H.; Meudec, E.; Véran, F.; W illiams, P.; Robillard, B.; Garcia, F.; Poncet-Legrand, C.; Cheynier, V. (2020) Multimethod Approach for Extensive Characterization of Gallnut Tannin Extracts. J. Agric. Food Chem. 68(47), 13426–13438.