Chemistry Reference
In-Depth Information
CH
2
OH
CH
2
OH
O
O
H
H
H
H
H
H
OH
H
OH
H
O
O
O
H
OH
H
OH
n
(a)
Amylose -
α
-1, 4 linkage
CH
2
OH
CH
2
OH
O
O
H
H
H
H
H
H
OH
H
OH
H
O
O
O
m
H
OH
H
OH
H
2
C
CH
2
OH
CH
2
OH
O
O
O
H
H
H
H
H
H
H
H
H
OH
H
OH
H
OH
H
O
O
O
O
H
OH
H
OH
H
OH
n
(b)
Amylopectin -
α
-1, 4 &
α
-1, 6 linkages
FIGURE 13.2
Chemical structure for the two main components of starch (a) amylose and (b) amylopectin.
consisting of D-anhydroglucose (C
6
H
11
O
5
) repeat units containing three hydroxyl
groups with the repeat units joined by
-1,4 ether linkages at C
1
and C
4
positions
(see
Figs. 13.1
and
13.3 [10]
). Cellulose provides strength and rigidity to plants
due to crystalline packing of the linear polymer chains.
The two other biopolymers found in plants are hemicelluloses and lignin; see
Fig. 13.3
. The amount of each constituent in a plant is dependent on both species
and growing conditions. Hemicellulose is very hydrophilic and is composed of
multiple polysaccharides of 5- and 6-carbon ring sugars with branched pendant
groups
[10]
. Lignin is an amorphous and highly complex cross-linked molecule
with aliphatic and aromatic constituents
[10]
. Lignin provides plant tissue and
individual fibers with compressive strength and stiffens the cell wall of the fibers
to protect polysaccharides, cellulose, and hemicelluloses from chemical and phys-
ical damage
[11]
. Due to the complex nature of lignin, it is very hard for the
majority of microorganisms to break it down. However, certain species of fungi
are capable of degrading lignin
[12]
. Lignin has been deemed the limiting step in
the degradation of wood and plant fibers.
β
