Page 221 - Advances in Textile Biotechnology

202 Advances in textile biotechnology

wool fibres can be estimated as follows: ∼95 μmol in the cuticle, ∼55 μmol
in the CMC, and ∼950 μmol in the cortex. Endogenous TGases are impli-
−1
cated in the process of maturation of keratin fibres and about 15 μmol g

of ε-(γ-glutamyl)lysine isopeptide crosslinks have been identified in the
enzymatic digest of untreated wool (Asquith et al., 1970). However, signifi -
cant amounts of free Gln binding sites are still available in the wool fi bre
for further TGase-mediated crosslinking and/or incorporation of primary
amines. The content of Lys, whose primary amino group may act as the acyl
−1
acceptor to form an isopeptide bond, is about 282 μmol g (∼2.8 mol%) in
untreated wool fi bres.
The pioneering work of Cortez et al. (2004) has demonstrated that TGase
can use the Gln residues of wool as substrate and that the enzymatic

approach to the modification of wool fibre properties is feasible. Both tissue

and microbial TGases proved to be effective in:
(i) maintaining and/or improving wool fi bre strength;
(ii) reducing the propensity of wool fabrics to shrink under normal
washing conditions; and
(iii) incorporating functional amine compounds into wool fi bres.
When wool fibres previously treated with protease, or with reducing/oxidis-

ing agents to simulate adverse industrial processing conditions likely to
lower fibre properties such as strength and handle, were exposed to the

action of tissue or microbial TGases, the enzymatic treatment was able to

restore the initial fibre properties, in particular tensile strength, thus reme-
diating the damages induced by proteolytic and/or chemical degradation.
TGases were able to improve strength of intact wool fi bres as well, though
to a lower extent. The higher the extent of fibre damage, the higher the

beneficial effect of TGase, indicating that more extensive degradation made

the fibre more accessible to the enzyme and facilitated the TGase-catalysed
crosslinking via ε-(γ-glutamyl)lysine bridges.
The potential of TGase to prevent/recover damages caused by the use of
common household detergents containing proteolytic enzymes and to
prolong the longevity of wool textiles was also demonstrated (Cortez et al.,
2005). Incubation with microbial TGase before detergent washing led to a
significant increase in tensile strength. After three washing cycles, the tensile

properties of TGase-treated wool samples decreased but to a much lower
extent than those not exposed to TGase. Treatment with TGase also had

beneficial effects on colour fastness because it lowered the amount of dye
released from the wool fabric into the washing liquor. All these results can
be explained in terms of higher crosslinking density induced by the enzyme
within the wool fibre matrix. The contribution of microbial TGase in improv-

ing yarn strength, decreasing area shrinkage and increasing wettability of
wool materials damaged by chemical (oxidative) or enzymatic (protease)

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