The present invention relates to compounds comprising the general formula (I), in which R1 and R2, which may be identical or different, are selected from the group comprising &mdash；H or a linear or branched alkyl group having from 1 to 6 carbon atoms or together form an aromatic or aliphatic ring with 5 or 6 atoms； Y and Z, which may be identical or different, are selected from the group comprising &mdash；H, &mdash；OH, &mdash；COOH, &mdash；OR3, &mdash；CH(OR3)COOH, in which R3 is selected from H, phenyl, benzyl, &mdash；CF3 or &mdash；CF2CF3, vinyl, allyl and a linear or branched alkyl group having from 1 to 6 carbon atoms.
