5.2 Occurrence in Nature
97
polymers present in algae, the fucoidan content in brown algae shows seasonal variation. Fucoidans further show more complex seasonal variation in their structure and
bioactivities (Fletcher et al. 2017).
Although not conventional sources of fucoidan, one study discovered the presence of fucoidan-like compounds in sea grasses (Kannan et al. 2013). The sulfated
polysaccharide extracted from the sea grass Halodule pinifolia contained fucoidanrelated monomers such as mannuronic acid, fucose and high level of uronic acid and
showed antioxidant activity, thus suggesting the possibility that fucoidans might not
be limited to brown algae and echinoderms alone.
Sea cucumbers are marine invertebrates which produce sulfated fucoidan as one
of their main polysaccharide components, the other being fucosylated glycosaminoglycan (Qin et al. 2018). Species of sea cucumber include Phylloporus proteus (Qin
et al. 2018) and Holothuria tubulosa (Chang et al. 2015).
5.3 Chemistry of Fucoidans
Fucoidans are sulfated polysaccharide with a sulfate group attached to some of the
monosaccharide units. The polysaccharide backbone is made up of mainly 1 → 3
linked or alternating 1 → 3 and 1 → 4 linked fucose units with some sulfate groups
attached to the oxygens. Branching occurs linking the mainly fucose backbone with
other monosaccharides such as rhamnose, xylose, arabinose, galactose and uronic
acid (Weelden et al. 2019). The level of branching, sulfation and polymer chain
configuration and monosaccharide units present within a given fucoidan depends on
the species, growth condition of the species and extraction method. These structural
variations also result in significant variation in the activities of the fucoidans.
Peng et al. (2018) reported fucoidan from Kjellmaniella crassifolia which contains
71.68% carbohydrate and 20.04% sulfate with 31.89% of the monosaccharides being
fucose and 23.54% galactose. Wei et al. (2019) reported fucose and galactose contents
of 77.4% and 13.9%, respectively, in fucose extracted from brown algae. Figure 5.1
shows different backbone structures of fucoidans from different sources showing
1 → 3 and 1 → 4 linkages and example of a sulfate attachment (Weelden et al.
2019).
Fucoidans are polydisperse such that within any given sample, the molecular
weight and degree of polymerization of each fucoidan polymer chain varies. This
is not uncommon characteristics of polymers. Methods such as mass spectrometry,
gas chromatography, MALDI-TOF and NMR are available for characterization of
fucoidan, and these have been employed in understanding the chemical structure
of fucoidan from different sources. In addition to the polydispersity, the average
molecular weight, configuration and degree of branching vary for fucoidans from
different sources (Fitton et al. 2015a, b). The fucoidans from sea cucumber tend to
have less complex structure and species relationship. For example, fucoidans from
97
polymers present in algae, the fucoidan content in brown algae shows seasonal variation. Fucoidans further show more complex seasonal variation in their structure and
bioactivities (Fletcher et al. 2017).
Although not conventional sources of fucoidan, one study discovered the presence of fucoidan-like compounds in sea grasses (Kannan et al. 2013). The sulfated
polysaccharide extracted from the sea grass Halodule pinifolia contained fucoidanrelated monomers such as mannuronic acid, fucose and high level of uronic acid and
showed antioxidant activity, thus suggesting the possibility that fucoidans might not
be limited to brown algae and echinoderms alone.
Sea cucumbers are marine invertebrates which produce sulfated fucoidan as one
of their main polysaccharide components, the other being fucosylated glycosaminoglycan (Qin et al. 2018). Species of sea cucumber include Phylloporus proteus (Qin
et al. 2018) and Holothuria tubulosa (Chang et al. 2015).
5.3 Chemistry of Fucoidans
Fucoidans are sulfated polysaccharide with a sulfate group attached to some of the
monosaccharide units. The polysaccharide backbone is made up of mainly 1 → 3
linked or alternating 1 → 3 and 1 → 4 linked fucose units with some sulfate groups
attached to the oxygens. Branching occurs linking the mainly fucose backbone with
other monosaccharides such as rhamnose, xylose, arabinose, galactose and uronic
acid (Weelden et al. 2019). The level of branching, sulfation and polymer chain
configuration and monosaccharide units present within a given fucoidan depends on
the species, growth condition of the species and extraction method. These structural
variations also result in significant variation in the activities of the fucoidans.
Peng et al. (2018) reported fucoidan from Kjellmaniella crassifolia which contains
71.68% carbohydrate and 20.04% sulfate with 31.89% of the monosaccharides being
fucose and 23.54% galactose. Wei et al. (2019) reported fucose and galactose contents
of 77.4% and 13.9%, respectively, in fucose extracted from brown algae. Figure 5.1
shows different backbone structures of fucoidans from different sources showing
1 → 3 and 1 → 4 linkages and example of a sulfate attachment (Weelden et al.
2019).
Fucoidans are polydisperse such that within any given sample, the molecular
weight and degree of polymerization of each fucoidan polymer chain varies. This
is not uncommon characteristics of polymers. Methods such as mass spectrometry,
gas chromatography, MALDI-TOF and NMR are available for characterization of
fucoidan, and these have been employed in understanding the chemical structure
of fucoidan from different sources. In addition to the polydispersity, the average
molecular weight, configuration and degree of branching vary for fucoidans from
different sources (Fitton et al. 2015a, b). The fucoidans from sea cucumber tend to
have less complex structure and species relationship. For example, fucoidans from