Page 230 - Advances in Textile Biotechnology

Functionalisation of wool and silk fi bres using enzymes 211

thermal stability and gel formation ability of isolated chicken breast myo-

fibril proteins, and the potential of tyrosinase to modify the fi rmness, water-
holding capacity, and microstructure of cooked chicken breast meat
homogenate gels were recently investigated (Lantto et al., 2007b). The
results showed that tyrosinase was effective in crosslinking myofi brillar
proteins. Crosslinking resulted in enhanced thermal properties, improved
gel-forming ability and gel properties of the meat protein systems. Particu-
larly interesting is the contribution of tyrosinase to improve water-holding
capacity, a target that could not be achieved by TGase-aided crosslinking
alone. In an attempt to tailor the textural and nutritional properties of food
polymers and to develop novel food formulations, Selinheimo et al. (2008)
studied the ability of two oxidative enzymes, the tyrosinase from T. reesei
and the laccase from Trametes hirsuta, to catalyse the conjugation between
proteins and carbohydrates. The results reported indicate that both enzymes
were able to catalyse the conjugation between the protein substrate casein
and the phenolic acids of hydrolysed oat spelt xylan, although to a different

extent. The higher efficiency of tyrosinase to crosslink casein was confi rmed,
but the possible inhibitory effect of phenolic acids added to the reaction
system was also highlighted. To fully exploit the potential of these enzymes
for the conjugation of food polymers, further optimisation of the reaction
system is needed.

Biopolymer conjugation
The ability of fungal tyrosinases to crosslink biopolymers has been exten-
sively investigated using several types of substrates such as proteins and
polysaccharides. Tyrosinases produce quinones, which are prone to react
non-enzymatically with nucleophilic moieties, such as lysyl, tyrosyl, cysteinyl
and histidinyl residues of proteins and primary amino groups of other bio-
polymers (for example chitosan) resulting in formation of crosslinks in the
protein structures or formation of polymer conjugates.
Chitosan has been widely used as model substrate to demonstrate the
potential of tyrosinase-catalysed polymer modifi cation. Payne et al. (1996)
devised an enzymatic strategy to modify this natural polymer by binding
tyrosinase-oxidised phenolic reactants to the polysaccharide chains, thus
obtaining a polymer with new properties. Interestingly, the enzymatic
approach was extended to the synthetic polymer poly(4-hydroxystyrene),
whose tyrosinase-oxidised phenolic moieties were grafted with aniline or
chitosan, thus proving the validity of the concept of enzymatic polymer
grafting (Shao et al., 1999). Tyrosinase-aided grafting of chlorogenic acid
onto chitosan under homogeneous conditions allowed widening of the
water solubility window of the polymer under alkaline conditions (Kumar
et al., 1999). Gelation of chitosan was enhanced by reaction with small

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