Page 231 - Advances in Textile Biotechnology

212 Advances in textile biotechnology

molecular weight freely diffusible reactive o-quinone species obtained by
tyrosinase oxidation of p-cresol (Kumar et al., 2000). The enzymatic grafting
of phenolic compounds containing carboxyl groups allowed conferring on
chitosan the ability to absorb cationic dyestuffs from wastewaters (Chao
et al., 2004). By using dopamine as tyrosinase substrate, water-resistant
adhesive properties were imparted on chitosan (Yamada et al., 2000 and
2008). Novel bio-based functional coatings for packaging materials for
foodstuffs were developed by tyrosinase-catalysed grafting of octyl or
dodecyl gallate onto chitosan and the coated polypropylene or paper sheets
resulted in strong antimicrobial activity and effective barrier effect against
oxygen transmission under dry conditions (Vartiainen et al., 2008).
Chen et al. (2001) tried to disclose details of the quinone-driven conjuga-
tion of biopolymers by mimicking quinone-based natural processes, such as
the transformation of animal secretions into strong adhesives (e.g. setting
of mussel glue) or the sclerotisation of cuticle in insects. Various biologically
active proteins were coupled to chitosan by means of a series of phenolic
coupling precursors. In most cases, the protein–polysaccharide coupling was
favoured by the phenolic precursor indicating that the accessibility of
surface Tyr residues in globular proteins might be a limiting factor for the
yield of the reaction, although it might play a key role in terms of selectiv-

ity and specificity of the reaction. All the proteins coupled with chitosan
maintained their biological activity. Owing to the more open structure of
gelatine compared with the globular proteins previously investigated, tyros-
inase was able to oxidise the protein-bound Tyr residues and the quinone
species thus formed could bind to the amino group of chitosan leading to
formation of gelatine–chitosan conjugates (Chen et al., 2002). Rheological
measurements gave evidence of the conjugation. Properties of these chito-
san–gelatine gels and their potential use for in situ applications were further
investigated by Chen et al. (2003a). This approach was further extended to
grafting casein-derived peptides onto chitosan with the aim of exploiting
food processing by-products for the production of environmentally friendly
polymers with useful functional properties (Aberg et al., 2004).
To overcome the difficulties related to accessibility of Tyr residues in

globular protein the fusion proteins technology was exploited to produce a
five Tyr residues tagged green fluorescent protein (Chen et al., 2003b). The

Tyr tail was designed to facilitate the tyrosinase-catalysed activation, a
prerequisite for the effective formation of protein–chitosan conjugates.
Because of the pH-responsive properties and the electrostatic nature of
chitosan, these conjugates could be selectively deposited onto micropat-
terned surfaces in response to an applied voltage, thus paving the way to
the production of bioactive microdevices. The protein tagging technique
was further exploited by Lewandowski et al. (2006) for a non-chromato-
graphic, fully enzymatic approach aiming at recovering proteins from cell

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