Cell Wall Polysaccharides of Marine Algae 22.3 Isolation from Algal Raw Material 555
Part D | 22.3
ˇ-D-Xylp instead of uronic acid (Fig. 22.2h). Ulvans
isolated from several Ulvales species are composed of
variable proportions of these disaccharides. Table 22.8
summarizes various oligosaccharides defined as structural fragments of ulvans.
22.2.5 Other Polysaccharides
Cell walls of many green algae contain alkali soluble
linear (1 ! 4)-ˇ-D-glucuronans [22.25, 157–159]. Sulfated rhamnans have been isolated from Monostroma
nitidum and Monostroma latissinum (Ulotrichales,
Chlorophyta) [22.25, 160–165] and from Gayralia
oxysperma (Ulvales, Chlorophyta) [22.25, 166]. Similar polysaccharides but in smaller amounts have been
detected in Bryopsis plumosa (Bryopsidales, Chlorophyta) [22.19]. These polysaccharides have mainly
(1 ! 2)-linked, but also (1 ! 3) and/or (1 ! 4)-linked
partially sulfated ˛-L-Rhap units. Moreover, they have
single stubs of uronic acid residues as side chains.
Rhamnan sulfate from Monostroma nitidum consists of
(1 ! 3)-linked ˛-L-Rhap residues, some of which are
sulfated mainly at O-2 [22.162]. Minor amounts of internal (1 ! 2)-linked and branched ˛-L-Rhap linkages
have also been found. Branched sulfated glucorhamnan has been isolated from the same alga [22.162].
This polysaccharide is mainly composed of (1 ! 2)
and (1 ! 3)-linked ˛-L-Rhap (1 W 2) partially sulfated
at the O-3 and O-2 positions, respectively. In addition, (1 ! 4)-linked ˇ-D-Glcp fragments are bound at
O-2 of some (1 ! 3)-linked backbone units. By contrast, polysaccharide from Monostroma latissinum is
defined as highly sulfated rhamnan composed mainly of
(1 ! 2)-linked ˛-L-Rhap residues with sulfate groups
substituted at O-3 and/or O-4 [22.163]. Sulfated heterorhamnan isolated from Gayralia oxysperma has
(1 ! 3) and (1 ! 2)-linked ˛-L-Rhap units in the backbone [22.166]. The latter units are partially substituted
at C-3 by side chains containing single GlcpA, GalpA
or Xylp. Both types of Rhap units are partially sulfated
at O-2 and/or O-4; side chain uronic acids are also sulfated but only at O-2.
Sulfated xylomannans, linear or containing single
stubs of ˇ-D-Xylp, or 3-O-methyl-ˇ-D-Xylp at O-2,
have been described for many red algae. Branched sulfated xylomannans (33222 kDa) have been isolated
from two species of the genus Chondrophycus (Ceramiales, Rhodophyta) [22.167]. These polysaccharides
consist of (1 ! 4)-linked ˇ-D-Manp2S backbone carrying stubs (1525%) of single ˇ-D-Xylp (7080%)
and ˇ-D-Manp2S (2030%). Several fractions from
Nothogenia fastigiata (Nemaliales, Rhodophyta) have
been identified as xylomannans with a backbone of
(1 ! 3)-linked ˛-D-Manp sulfated at the O-2 and
O-6 positions and single stubs of ˇ-D-Xylp at O2 [22.168, 169]. Sulfated xylomannan (150 kDa) has
been isolated from Sebdenia polydactyla (Sebdeniales,
Rhodophyta) [22.170]. This polysaccharide contains
a backbone of (1 ! 3)-linked ˛-D-Manp units, partially substituted with a single stub of ˇ-D-Xylp at
O-6. The main polysaccharide fraction isolated from
Nemalion helminthoides (Nemaliales, Rhodophyta) has
been identified as (1 ! 3)-˛-D-mannan sulfated at
the O-4 and O-6 positions; other fractions are similar mannans but they contain single stubs of ˇD-Xylp [22.171, 172]. Sulfated arabinopyranan has
been isolated from the green alga Enteromorpha
clathrata [22.173]. The backbone of this polysaccharide is mainly composed of (1 ! 4)-linked ˇ-L-Arap
residues, partially sulfated at the O-3 position. Two sulfated polysaccharides, i. e., arabinan and arabinogalactan, have been isolated from Codium dwarkense (Bryopsidales, Chlorophyta) [22.174]. Two water-soluble
sulfated polysaccharides from Codium vermilara (Bryopsidales, Chlorophyta) have been identified as (i) partially 2-O-sulfated (1 ! 4)-ˇ-D-mannan and (ii) (1 !
3)-ˇ-L-arabinopyranan highly sulfated at the O-2 and
O-4 positions [22.23, 24].
22.3 Isolation from Algal Raw Material
Crystalline, fibrilar, and matrix polysaccharides of
algal cell walls can be successfully isolated from
raw material by subsequent extractions. The isolation is based on the difference in solubility of these
polysaccharides in various media at neutral, acidic,
or alkali conditions. Usually matrix polysaccharides
are well soluble in hot water, hemicellulose components are soluble in alkali solutions, while crystalline cellulose and, in some cases, xylans or mannans, remain insoluble at these conditions. Before
subsequent extraction of polysaccharides, raw material is usually washed with organic solvents to remove lipids, pigments, and other small molecules, and
then washed with distilled water to remove small hydrophilic molecules. Finally, raw material is dried and
milled.
Part D | 22.3
ˇ-D-Xylp instead of uronic acid (Fig. 22.2h). Ulvans
isolated from several Ulvales species are composed of
variable proportions of these disaccharides. Table 22.8
summarizes various oligosaccharides defined as structural fragments of ulvans.
22.2.5 Other Polysaccharides
Cell walls of many green algae contain alkali soluble
linear (1 ! 4)-ˇ-D-glucuronans [22.25, 157–159]. Sulfated rhamnans have been isolated from Monostroma
nitidum and Monostroma latissinum (Ulotrichales,
Chlorophyta) [22.25, 160–165] and from Gayralia
oxysperma (Ulvales, Chlorophyta) [22.25, 166]. Similar polysaccharides but in smaller amounts have been
detected in Bryopsis plumosa (Bryopsidales, Chlorophyta) [22.19]. These polysaccharides have mainly
(1 ! 2)-linked, but also (1 ! 3) and/or (1 ! 4)-linked
partially sulfated ˛-L-Rhap units. Moreover, they have
single stubs of uronic acid residues as side chains.
Rhamnan sulfate from Monostroma nitidum consists of
(1 ! 3)-linked ˛-L-Rhap residues, some of which are
sulfated mainly at O-2 [22.162]. Minor amounts of internal (1 ! 2)-linked and branched ˛-L-Rhap linkages
have also been found. Branched sulfated glucorhamnan has been isolated from the same alga [22.162].
This polysaccharide is mainly composed of (1 ! 2)
and (1 ! 3)-linked ˛-L-Rhap (1 W 2) partially sulfated
at the O-3 and O-2 positions, respectively. In addition, (1 ! 4)-linked ˇ-D-Glcp fragments are bound at
O-2 of some (1 ! 3)-linked backbone units. By contrast, polysaccharide from Monostroma latissinum is
defined as highly sulfated rhamnan composed mainly of
(1 ! 2)-linked ˛-L-Rhap residues with sulfate groups
substituted at O-3 and/or O-4 [22.163]. Sulfated heterorhamnan isolated from Gayralia oxysperma has
(1 ! 3) and (1 ! 2)-linked ˛-L-Rhap units in the backbone [22.166]. The latter units are partially substituted
at C-3 by side chains containing single GlcpA, GalpA
or Xylp. Both types of Rhap units are partially sulfated
at O-2 and/or O-4; side chain uronic acids are also sulfated but only at O-2.
Sulfated xylomannans, linear or containing single
stubs of ˇ-D-Xylp, or 3-O-methyl-ˇ-D-Xylp at O-2,
have been described for many red algae. Branched sulfated xylomannans (33222 kDa) have been isolated
from two species of the genus Chondrophycus (Ceramiales, Rhodophyta) [22.167]. These polysaccharides
consist of (1 ! 4)-linked ˇ-D-Manp2S backbone carrying stubs (1525%) of single ˇ-D-Xylp (7080%)
and ˇ-D-Manp2S (2030%). Several fractions from
Nothogenia fastigiata (Nemaliales, Rhodophyta) have
been identified as xylomannans with a backbone of
(1 ! 3)-linked ˛-D-Manp sulfated at the O-2 and
O-6 positions and single stubs of ˇ-D-Xylp at O2 [22.168, 169]. Sulfated xylomannan (150 kDa) has
been isolated from Sebdenia polydactyla (Sebdeniales,
Rhodophyta) [22.170]. This polysaccharide contains
a backbone of (1 ! 3)-linked ˛-D-Manp units, partially substituted with a single stub of ˇ-D-Xylp at
O-6. The main polysaccharide fraction isolated from
Nemalion helminthoides (Nemaliales, Rhodophyta) has
been identified as (1 ! 3)-˛-D-mannan sulfated at
the O-4 and O-6 positions; other fractions are similar mannans but they contain single stubs of ˇD-Xylp [22.171, 172]. Sulfated arabinopyranan has
been isolated from the green alga Enteromorpha
clathrata [22.173]. The backbone of this polysaccharide is mainly composed of (1 ! 4)-linked ˇ-L-Arap
residues, partially sulfated at the O-3 position. Two sulfated polysaccharides, i. e., arabinan and arabinogalactan, have been isolated from Codium dwarkense (Bryopsidales, Chlorophyta) [22.174]. Two water-soluble
sulfated polysaccharides from Codium vermilara (Bryopsidales, Chlorophyta) have been identified as (i) partially 2-O-sulfated (1 ! 4)-ˇ-D-mannan and (ii) (1 !
3)-ˇ-L-arabinopyranan highly sulfated at the O-2 and
O-4 positions [22.23, 24].
22.3 Isolation from Algal Raw Material
Crystalline, fibrilar, and matrix polysaccharides of
algal cell walls can be successfully isolated from
raw material by subsequent extractions. The isolation is based on the difference in solubility of these
polysaccharides in various media at neutral, acidic,
or alkali conditions. Usually matrix polysaccharides
are well soluble in hot water, hemicellulose components are soluble in alkali solutions, while crystalline cellulose and, in some cases, xylans or mannans, remain insoluble at these conditions. Before
subsequent extraction of polysaccharides, raw material is usually washed with organic solvents to remove lipids, pigments, and other small molecules, and
then washed with distilled water to remove small hydrophilic molecules. Finally, raw material is dried and
milled.