Bitterness and astringency of flavan-3-ol monomers, dimers and trimers

Intensity of astringency and bitterness of seven flavonoid compounds was evaluated by a time-intensity (TI) procedure. Eighteen trained judges rated intensity continuously from ingestion, through expectoration at 10s until extinction of the sensation. The seven stimuli included two flavan-3-ol monomers, (+)-catechin and (-)-epicatechin, three dimers and two trimers synthesised from catechin or epicatechin by condensation with (+)-dihydroquercitin. As the degree of polymerisation increased, maximum bitterness intensity (I(max) and total duration (T(tot)) decreased whereas astringency I(max) increased. The monomers were significantly higher in bitterness at I(max) than the dimers, which were significantly higher than the trimers. Astringency I(max) of the monomers was lower than the dimers or trimers, although no significant difference was found in T(tot) among the polymer classes. The bond linking the monomeric units had an influence on both sensory properties. The catechin-catechin dimer linked by a 4 leads to 6 bond was more bitter than both catechin-(4 leads to 8)-catechin and catechin-(4 leads to 8)-epicatechin. Astringency was affected by both the specific linkage and the identity of the monomeric units with the dimer, catechin-(4 leads to 8)-catechin, being lower in astringency than either catechin-(4 leads to 6)-catechin or catechin-(4 leads to 8)-epicatechin.