Multimethod Approach for Extensive Characterization of Gallnut Tannin Extracts

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Abstract
Gallotannins extracted from gallnuts are commonly added to wine to improve its properties. They consist of mixtures of galloylester derivatives of glucose. However, their composition and properties are not well established. In this study, methods based on liquid chromatography coupled to UV-visible detection and mass spectrometry, size exclusion chromatography and 1D (31P) and 2D (1H DOSY, 31P TOCSY, 1H/13C HSQC, HMBC) NMR spectroscopy have been implemented for extensive chemical characterization of three commercial gallnut tannin extracts. Differences in the proportions of the different constituents (gallic, digallic, trigallic acids, galloylglucose derivatives) and in the structure and molecular weight distributions of gallotannins were demonstrated between the three extracts, with chains containing 8.5, 12.2, and 12.4 galloyl groups in average for TAN A, B1, and B2, respectively. The antioxidant capacities of the extracts, evaluated using the ABTS method, were similar and related mostly to their total tannin content, with only limited impact of the tannin composition.
Funding Information
  • European Regional Development Fund
  • R?gion Grand-Est

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