Addition of certain amino acids (L-tryptophan, L-histidine, L-cysteine
and L-cystine) to model solutions of caffeic acid and hydroxytyrosol
(the two most characteristic o-diphenols of ripe olives) improved the
dark colour obtained after oxidation. A detailed study carried out wit
h L-cysteine and caffeic acid showed that, after an initial inhibitory
effect, increasing concentrations of amino acid led to darker solutio
ns. The same effect was also found in hydroxytyrosol solutions with in
creasing amounts (2-8 mM) of cysteine without lag phase, except for 10
mM level. Cysteine also produced darker colour with oxidised storage
brine of ripe olives. These results open the door to a possible use of
this amino acid as additive or aid in processing to produce darker an
d homogeneous ripe olives. (C) 1998 Elsevier Science Ltd. All lights r
eserved.