Biology Reference
In-Depth Information
The preparation of beads from the resulting amylose-grafted
alginate was attempted by adding its alkaline solution into calcium
chloride aqueous solution. Consequently, beads were obtained from
the amylose-grafted alginate containing shorter amylose graft chains
(DP < 50), whereas that containing longer amylose graft chains (DP
= 100) did not afford the formation of beads. This result indicated
that the longer amylose graft chains attached to the alginate main-
chain disturbed the formation of the stable matrices composed
of the cross-linked calcium alginates, resulting in difficulty in the
formation of beads. In addition, enzymatic disintegradability of
the beads was investigated by
-amylase-catalyzed reaction. When
the beads obtained from the amylose-grafted alginate containing
shorter amylose graft chains were kept standing in the presence
of
β
β
°
C for 6 h, the solution
gradually became turbid, indicating disintegration of the beads.
The chemoenzymatic method was also investigated using
another anionic polysaccharide, i.e., xanthen gum, as a main-
chain of amylose-grafted polymer. Xanthan gum, which is a water-
soluble polysaccharide produced by
-amylase in a stirred acetate buffer at 40
, is a
representative food hydrocolloid [15]. It has a cellulose-type main-
chain (
Xanthomonas campestris
β
-(1
→
4)-glucan) with trisaccharide side-chains (mannose-
β
→
β
→
α
→
3)-) attached
to alternate glucose units in the main-chain [16]. The
-(1
4)-glucuronic acid-
-(1
2)-mannose-
-(1
α
-mannoside
β
unit is acetylated at position 6 and the
-mannoside unit is partially
pyruvated at positions 4 and 6. Because the side-chain contains
carboxylate groups, xanthan gum is an anionic polysaccharide.
The chemoenzymatic synthesis of an amylose-grafted xanthan
gum was performed as follows (Fig. 6.8) [17]. An amine-function-
alized maltooligosaccharide was chemically introduced to xanthan
gum by condensation with its carboxylates using a condensing agent
to produce a maltooligosaccharide-grafted xanthan gum. Then, a
phosphorylase-catalyzed enzymatic polymerization of Glc-1-P from
the graft chain ends on the xanthan gum derivative was performed,
giving an amylose-grafted xanthan gum.
The product formed a gel with an ionic liquid, which was
converted into a hydrogel with high water content by replacement
of the ionic liquid with water. The ionically cross-linked hydrogel
was also provided by soaking the primary formed hydrogel in FeCl
3
aqueous solution. When the mechanical properties of the ionically
cross-linked hydrogels with Fe
3+
were evaluated by compressive
