title: Use of antioxidants in extraction of tannins from walnut plants.
abstract: The radial diffusion assay was applied to estimate the amount of total tannins in extracts from walnut plant materials. We found that the protein-precipitating activity of the tannin extracts were increased by 30-75 % when antioxidants (ascorbic acid or sodium metabisulfite, 5.5 mM) were added in extraction solvents (50% aqueous methanol). The extracts obtained with Na2S2O5 were much less brown than control. Moreover, two-dimensional thin-layer chromatography revealed some additional polyphenolic compounds in the extracts made with Na2S2O5. These results suggest that the amount of tannins and/or their protein-precipitating property may be strongly affected by oxidation events during extraction procedure. The addition of antioxidants in the extraction solvents is useful to limit this problem.
authors.affiliation: Station d'Amélioration des Arbres Forestiers, Institut National de la Recherche Agronomique, Ardon, F-45160, Olivet, France.
authors.forename: S
authors.initials: S
authors.lastname: Peng
authors.forename: C
authors.initials: C
authors.lastname: Jay-Allemand