ABSTRACT
In the study, hair colouring by utilising enzymatic oxidation
of nine species of bio-catechols, which are biobased materials having the catechol
(o-dihydroxybenzene) group, was examined. The
bio-catechols used are (+)-catechin (Cat), (-)-epicatechin (EC), L-3,4-dihydroxyphenylalanine (DOPA), hematoxylin
(HX), brazilin (BZ), rosmarinic acid (RA), caffeic acid (CA), chlorogenic acid
(ChA) or ellagic acid (EA). The dyeability of human white hair samples dyed by
two kinds of dyeing methods using the bio-catechols was compared. First one is dyeing
hair during the enzymatic oxidation of a bio-catechol dye precursor in a dye
solution (simultaneous oxidation dyeing method). Second one is dyeing hair by
oxidising enzymatically the precursor on hair, which is pre-treated with a
bio-catechol solution (post-oxidation dyeing method). The results show that the
bio-catechols except EA are oxidised to give colourants and Cat, EC, DOPA, HX
and BZ are available for hair dyeing. Overall, the dyeability of simultaneous
oxidation dyeing method is higher than that of post-oxidation one. The colour
of the hair dyed by simultaneous method is yellowish brown for Cat or EC, grey
for DOPA, dark yellowish brown for HX or reddish brown for BZ, respectively.
The most vivid or deepest colour of dyed hair is obtained by dyeing with Cat or
HX, respectively, in the simultaneous technique. It was found that the
bio-catechols having chroman (3, 4-dihydro-2H-1-benzopyran)
structure in the molecule such as Cat, EC, HX and BZ are useful for hair
colouring.