General Properties, Occurrence, and Preparation
1.2
79
β-L-arabinofuranosyl-(1→3)-α-L-arabinopyranosyl linked 1→6 to the D-galactopyranose
chain [72,73].
Xyloglucans and xylans are widely distributed, found in most plant cell walls, see > Fig. 6
for the structures of these hemicelluloses. Glucurono-arabino-xylan is also widely distributed,
especially in soft-wood trees [74]. Glucuronoxylan is prevalent in hard-wood trees [74]. Hemicellulose composed exclusively of D-mannopyranose is found in palm seed endosperm [70],
where it is known as vegetable ivory or ivory nut mannan. Galactomannan are particularly
found in soft-wood trees, but also are found in the seedpods of the locust bean. In particular,
a galactomannan known as guar gum has been obtained from the seeds of the legume, guar,
grown in the semiarid regions of India. It has found widespread use as a thickening agent in
food products. Arabinogalactans are prevalent in soft woods such as, larch, black spruce, Douglas fir, cedar, and juniper [74]. Segments of the structures of D-xyloglucan and D-xylan are
shown in > Fig. 6.
6.1 Properties and Occurrence of Pectin
Pectins are related to hemicelluloses and occur in the plant cell wall in low amounts of 1–5%
(w/w). They are more prevalent in fruits, for example, apple pulp (10–15%) and in orange
and lemon rinds (20–30%). Pectins do have a number of chemical and physical properties that
differ from the hemicelluloses. They are composed of D-galactopyranosyl uronic acids linked
α-(1→4) and have a relatively wide percentage of the carboxyl groups esterified with methyl
groups. There also is a small amount (1 in ∼25 uronic acid residues) with L-rhamnopyranosyl
(6-deoxy-L-mannopyranosyl) residues linked α-(1→2) to the D-galactopyranosyl uronic acid
residues. In addition, pectins also have 2-O-acetyl or 3-O-acetyl ester groups attached to the
uronic acids [75]. The average molecular weight can vary from 20,000 to 400,000 Da, with
a typical average molecular weight of 100,000 Da. Pectins act in plants as an intercellular
cementing agent that provides body to fruits, and of course, it is used in foods as a gelling
agent, especially in the preparation of jellies and confections.
7 Cellulose-like Polysaccharides Containing
N -Acetyl-D-Glucosamine and D-Glucosamine
There are several polysaccharides containing the β-(1→4) structure, but with monomer
residues other than D-glucopyranose, such as N-acetyl-D-glucosamine, D-glucosamine,
N-acetyl-D-muramic acid.
7.1 Properties and Occurrence of Chitin
Chitin is a polysaccharides with the exact same structure as cellulose but containing N-acetylD-glucosamine or D-glucosamine and are fairly widely distributed [76] (see > Fig. 6 for the
structure of a segment of chitin). It is a structural polysaccharide that forms fibers, is water
impermeable, and replaces cellulose in the cell walls of many species of lower organisms,
1.2
79
β-L-arabinofuranosyl-(1→3)-α-L-arabinopyranosyl linked 1→6 to the D-galactopyranose
chain [72,73].
Xyloglucans and xylans are widely distributed, found in most plant cell walls, see > Fig. 6
for the structures of these hemicelluloses. Glucurono-arabino-xylan is also widely distributed,
especially in soft-wood trees [74]. Glucuronoxylan is prevalent in hard-wood trees [74]. Hemicellulose composed exclusively of D-mannopyranose is found in palm seed endosperm [70],
where it is known as vegetable ivory or ivory nut mannan. Galactomannan are particularly
found in soft-wood trees, but also are found in the seedpods of the locust bean. In particular,
a galactomannan known as guar gum has been obtained from the seeds of the legume, guar,
grown in the semiarid regions of India. It has found widespread use as a thickening agent in
food products. Arabinogalactans are prevalent in soft woods such as, larch, black spruce, Douglas fir, cedar, and juniper [74]. Segments of the structures of D-xyloglucan and D-xylan are
shown in > Fig. 6.
6.1 Properties and Occurrence of Pectin
Pectins are related to hemicelluloses and occur in the plant cell wall in low amounts of 1–5%
(w/w). They are more prevalent in fruits, for example, apple pulp (10–15%) and in orange
and lemon rinds (20–30%). Pectins do have a number of chemical and physical properties that
differ from the hemicelluloses. They are composed of D-galactopyranosyl uronic acids linked
α-(1→4) and have a relatively wide percentage of the carboxyl groups esterified with methyl
groups. There also is a small amount (1 in ∼25 uronic acid residues) with L-rhamnopyranosyl
(6-deoxy-L-mannopyranosyl) residues linked α-(1→2) to the D-galactopyranosyl uronic acid
residues. In addition, pectins also have 2-O-acetyl or 3-O-acetyl ester groups attached to the
uronic acids [75]. The average molecular weight can vary from 20,000 to 400,000 Da, with
a typical average molecular weight of 100,000 Da. Pectins act in plants as an intercellular
cementing agent that provides body to fruits, and of course, it is used in foods as a gelling
agent, especially in the preparation of jellies and confections.
7 Cellulose-like Polysaccharides Containing
N -Acetyl-D-Glucosamine and D-Glucosamine
There are several polysaccharides containing the β-(1→4) structure, but with monomer
residues other than D-glucopyranose, such as N-acetyl-D-glucosamine, D-glucosamine,
N-acetyl-D-muramic acid.
7.1 Properties and Occurrence of Chitin
Chitin is a polysaccharides with the exact same structure as cellulose but containing N-acetylD-glucosamine or D-glucosamine and are fairly widely distributed [76] (see > Fig. 6 for the
structure of a segment of chitin). It is a structural polysaccharide that forms fibers, is water
impermeable, and replaces cellulose in the cell walls of many species of lower organisms,