Method of preparing purified polyphenolic flavan-3-ol type extracts ("pyonogenols") from various vegetable starting materials, characterised in that it comprises the steps consisting in exhaustively extracting the crude vegetable matter first with water, in filtering the mixture, in centrifuging the filtrate after it has been left in the cold, in exhaustively extracting the supernatant with ethyl acetate, in separating the organic phase containing the extract, in distilling this phase under reduced pressure to recover the ethyl acetate, in taking up the aqueous residue with water and in lyophilising the aqueous solution obtained, this procedure yielding the desired extract in the form of a completely water-soluble powder. Use of the extract obtained as an active substance having a trapping effect on free radicals, in pharmaceutical, dietary and cosmetic products.
