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Enzymatic functionalization of cellulosic fi bres for textiles 269

L-Fucpa1

2
(Galpb1) 0–1 (Galpb1) 0–1

2 2
Xylpa1 Xylpa1 Xylpa1

6 6 6
4Glcpb1 4Glcpb1 4Glcpb1 4Glcpb1
n
11.1 A common structure of XGs based on a Glc 4 Xyl 3 core structure.
Variable regioselective addition of galactosyl residues on one or two
xylosyl branches further extends the core. Extension of Gal with an
α-L-fucosyl residue (boxed) distinguishes XGs found in dicot primary
cell walls from those found in seeds, cf. the molecular structure
shown in Fig. 11.4.

species, including the tamarind (Tamarindus indica) and jatoba (Hymenaea
courbaril) trees, as well as the ornamental nasturtium plant (Tropaeolum
majus) (Buckeridge et al., 1997; Edwards et al., 1985; York et al., 1993). In
general, the seed XGs have the same basic oligosaccharide repeat structures
as those in the primary plant cell wall, but are distinguished by a lack of
terminal α(1 → 2)-linked l-fucosyl residues on the β-d-Galp-(1 → 2)-α-d-
Xylp(1 → 6)-d-Glcp sidechains (Buckeridge et al., 1997; Hoffman et al.,
2005; York et al., 1993) (Fig. 11.1). The importance of fucosyl residues in the
cellulose–XG interaction in vitro binding is unclear (Chambat et al., 2005;
Whitney et al., 2006; Zykwinska et al., 2005), although they appear to be of
little biological importance in vivo: mutant Arabidopsis plants that lack XG
fucosylation have normal growth and cell wall strength (Reiter, 2002).
However, selective enzymatic hydrolysis has indicated that the pendant
galactose residues are important in maintaining XG solubility (Shirakawa
et al., 1998; Whitney et al., 2006). The interested reader is referred to the
review by Zhou et al. (2007) for a more detailed overview of XG structure–
function relationships, including the effects on rheology and interactions
with cellulose.
Owing to their availability in large quantities, tree seeds, and especially
tamarind seed kernels, comprise the most relevant sources of XG for fun-
damental studies and industrial applications. ‘Tamarind kernel powder
−1
(TKP)’ is a large-scale (ca. 100 000 tonne y ) agricultural co-product from
the production of tamarind fruit pulp for the food industry (Rao and Sriv-
astava, 1973; Shankaracharya, 1998). De-oiled TKP contains ca. 60% XG
by mass, which can be readily extracted by aqueous solutions to produce
various crude preparations known as ‘tamarind gum’ (Gerard, 1980; Kumar

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