Page 240 - Advances in Textile Biotechnology

Functionalisation of wool and silk fi bres using enzymes 221

observed, indicating oxidation of the secondary substrates of laccase, i.e.,
wool, Cys, or Tyr. Lantto et al. calculated that with the laccase/HBT system
about 5% Cys and 20% Tyr residues present in the cuticle were oxidised.
However, only very low amounts of oxidised species were detected by XPS
analysis of the wool surface, probably because oxidised mediator molecules

that were absorbed or covalently bound to the fibre surface interfered with

measurements. When wool fibres were exposed to the action of two per-
oxidases, HRP and a peroxidase of fungal origin (NS51004), about 35–40%
of the Tyr residues located in the cuticle were oxidised based on H 2 O 2 con-
sumption (Lantto et al., 2005b). XPS and FTIR analyses could detect only

slight changes in surface chemistry of wool fibres incubated with the fungal
peroxidase.
The reaction of silk fibres with HRP and H 2 O 2 was investigated by study-

ing the intermediates enzymatically generated by means of electron para-
magnetic resonance (EPR) and UV/vis spectrophotometry (Oliva et al.,
2003). The time dependence of the EPR spectrum indicated that HRP

compound II was still present after 5 min of silk fibre oxidation, and this
was confirmed by spectrophotometric results. On the contrary, after about

10 min, only the presence of HRP compound I was detectable. The latter
species became weaker within a few weeks with sample ageing. Further-
more, both HRP compounds I and II were observed to decay in the pres-
ence of silk, the latter more quickly than the former. By contrast, these two
oxidised forms of HRP remained stable (compound I) or decayed more
slowly (compound II) without silk. This suggests that silk took part in the
reaction as an electron donor probably by oxidation of the Tyr side chains

of silk fibroin by HRP.
The peroxidase- and laccase-catalysed coloration of wool fibres has been

reported by Shin et al. (2001). In situ production of oligomers and polymers
from different phenolic compounds by HRP/H 2O 2 allowed different colours

to be obtained on wool fibres, from black to brown, grey, and yellow. To
avoid the use of H 2 O 2 , laccase was used to oxidise hydroquinone or ferulic
acid for the enzymatic dyeing of wool. Colour depth was sensitive to both
enzyme and phenol concentration. A mordanting treatment with chromium
compounds enhanced the fixation of the phenolic colouring matters onto

wool fibres. The enzymatic coloration of wool fibres was further investigated

by Tzanov et al. (2003), who applied a factorial experimental design to
understand the effect of different reaction parameters in an enzymatic
system comprising laccase, a dye precursor, and catechol or resorcinol as
dye modifiers. Different hues and depths of shade were obtained by varying

the concentration of the modifiers and the time of laccase treatment. By

coupling ultrasonic irradiation with cyclic voltammetry for the laccase-
mediated oxidation of 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate)
(ABTS) in the presence of wool fabrics, a high depth of wool coloration

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