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8 Ulvans
that the sulfate groups of ulvan generally attaches to either the second or third carbon
of the rhamnose unit or the second carbon of the xylose unit (Tabarsa et al. 2018).
The bioactivity of ulvans is affected by the molecular weight. The molecular
weight of ulvans varies between 100 and 8000 kDa (Lahaye 1998) although others
report it between 150 and 2000 kDa (Rioux and Turgeon 2015). Lower molecular weight has been shown to favor interactions with immune cells which aid
immunomodulatory and inflammatory activities (Chen et al. 2008; Jaswir and Monsur 2011). This superior bioactivity of lower molecular weight ulvan over higher
molecular weight ulvan is attributed to the ease of access into the cells and ease of
proton exchange as a result of lower molecular weight (Qi et al. 2005).
Each repeating unit within the ulvan structure plays a distinct role in the bioactivity
of ulvan. Rhamnose can aid in hyaluronic and collagen production in human fibroblast
dermal cells through interacting in biosynthetic pathways in the dermis (Adrien et al.
2017). The presence of functional groups such as sulfate and amine groups also
confers certain properties on the ulvan polymer. The repeated disaccharide units of
ulvans comprising mainly of uronic acid linked to sulfated rhamnose or xylose make
them applicable for modulation of cellular activities carried out by polysaccharides
in mammals. These properties make them applicable in areas such as wound healing,
tissue repair and antiviral activities.
While each repeating unit has its contributory role to the physicochemical and
bioactive properties of the ulvan, the configuration, order with which the repeating units are arranged within the polymeric structure, is also important. This in
turn affects the conformation of the ulvan molecules and consequently the overall
properties. Branching occurs usually at the 1.2 linked glucuronic acid linked to the
rhamnose (Kidgell 2019; Lahaye and Robic 2007). As with most polymers the level
of branching is related to properties such as crystallinity, thermal and mechanical
properties of the polymer.
Ulvans are soluble polysaccharides that dissolve in water to form a gel-like solution. Like all polymers, ulvans will increase the viscosity of the solution within which
it is dissolves in. The solution viscosity of ulvan depends on the pH and the presence of salts. At low to neutral pH, ulvan takes on a bead-like conformation which
aggregates in the presence of salts such as sodium chloride. Such solutions of ulvan
usually have low viscosity. In more alkaline environment, ulvan forms more viscous
solutions with higher gel strength (Lahaye and Robic 2007).
The biochemistry of ulvans varies for different sources as a result of variation in
the primary structure, molecular weight, branching and the polydisperse nature of the
polymer. These variation correlate with their bioactive properties. For instance, low
molecular weight ulvans have been shown to stimulate kidney macrophage better than
ulvans with higher molecular weights (Fernández-Díaz et al. 2017). There have been
studies which investigate the bioactive properties of crude ulvan extract and those
which separate the ulvan into different molecular weight fractions to investigate the
properties of specific molecular weight range, and other studies have extended to
modification of ulvans to control specific properties. Chemical properties such as
degree of sulfation can be modified by removal or addition of sulfate functional
groups such as solvolysis or base hydrolysis (Qi et al. 2012). The chain length of the
8 Ulvans
that the sulfate groups of ulvan generally attaches to either the second or third carbon
of the rhamnose unit or the second carbon of the xylose unit (Tabarsa et al. 2018).
The bioactivity of ulvans is affected by the molecular weight. The molecular
weight of ulvans varies between 100 and 8000 kDa (Lahaye 1998) although others
report it between 150 and 2000 kDa (Rioux and Turgeon 2015). Lower molecular weight has been shown to favor interactions with immune cells which aid
immunomodulatory and inflammatory activities (Chen et al. 2008; Jaswir and Monsur 2011). This superior bioactivity of lower molecular weight ulvan over higher
molecular weight ulvan is attributed to the ease of access into the cells and ease of
proton exchange as a result of lower molecular weight (Qi et al. 2005).
Each repeating unit within the ulvan structure plays a distinct role in the bioactivity
of ulvan. Rhamnose can aid in hyaluronic and collagen production in human fibroblast
dermal cells through interacting in biosynthetic pathways in the dermis (Adrien et al.
2017). The presence of functional groups such as sulfate and amine groups also
confers certain properties on the ulvan polymer. The repeated disaccharide units of
ulvans comprising mainly of uronic acid linked to sulfated rhamnose or xylose make
them applicable for modulation of cellular activities carried out by polysaccharides
in mammals. These properties make them applicable in areas such as wound healing,
tissue repair and antiviral activities.
While each repeating unit has its contributory role to the physicochemical and
bioactive properties of the ulvan, the configuration, order with which the repeating units are arranged within the polymeric structure, is also important. This in
turn affects the conformation of the ulvan molecules and consequently the overall
properties. Branching occurs usually at the 1.2 linked glucuronic acid linked to the
rhamnose (Kidgell 2019; Lahaye and Robic 2007). As with most polymers the level
of branching is related to properties such as crystallinity, thermal and mechanical
properties of the polymer.
Ulvans are soluble polysaccharides that dissolve in water to form a gel-like solution. Like all polymers, ulvans will increase the viscosity of the solution within which
it is dissolves in. The solution viscosity of ulvan depends on the pH and the presence of salts. At low to neutral pH, ulvan takes on a bead-like conformation which
aggregates in the presence of salts such as sodium chloride. Such solutions of ulvan
usually have low viscosity. In more alkaline environment, ulvan forms more viscous
solutions with higher gel strength (Lahaye and Robic 2007).
The biochemistry of ulvans varies for different sources as a result of variation in
the primary structure, molecular weight, branching and the polydisperse nature of the
polymer. These variation correlate with their bioactive properties. For instance, low
molecular weight ulvans have been shown to stimulate kidney macrophage better than
ulvans with higher molecular weights (Fernández-Díaz et al. 2017). There have been
studies which investigate the bioactive properties of crude ulvan extract and those
which separate the ulvan into different molecular weight fractions to investigate the
properties of specific molecular weight range, and other studies have extended to
modification of ulvans to control specific properties. Chemical properties such as
degree of sulfation can be modified by removal or addition of sulfate functional
groups such as solvolysis or base hydrolysis (Qi et al. 2012). The chain length of the