[Comparative study of different extraction methods and assays of tannins in some pteridophytes]

Various processes of extraction and quantitative analysis of a condensed tannin in a plant extract, which also includes some chlorogenic acids, have been examined. 60% methanol, at 50 degrees C, proved the most efficient extraction solvent. Several methods of analysis have been tried. The measure of the colour intensity obtained by the action of sulphuric vanilline on flavanols cannot be used because it depends on the tannin condensation stage. It is impossible to separate tannin from chlorogenic acids using the methods of adsorption by skin or nylon powders, or precipitation by polyvinylpyrrolidone. Only paper chromatography, followed by the distinct elution of the various phenolic compounds, allows the tannin evaluation by subtraction; but owing to the variability of the results, many more experiments are necessary. Some other processes are being studied.