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8 Ulvans
Unlike brown algae with a relatively complex reproductive cycle which makes
controlled cultivation in aquaculture more labor and cost intensive to be economically viable for commercial biopolymer production, the cultivation of green algae
is relatively simpler. Due to its relatively rapid growth rate and simpler cultivation
process, the ulvan species of green algae are more promising for the cultivation of
monocultures which will result in more uniform ulvan extracts. This is important in
developing standard formulations with specific bioactivities where factors such as
molecular weight and degree of sulfation are within shorter ranges. Some Ulva green
algae grow so easily that in situations where there is an environmental imbalance
in the aquatic ecosystem such as increase in nutrient content of the water this could
result in drastic population boom of green algae resulting in what is known as green
tides (Kidgell et al. 2019). The Ulva species have been identified as one of the algae
species which form algae blooms (Young and Gobler 2016). Ulva prolifera, a highly
productive Ulva can increase by 28% in population within a period of 24 h (Zhang
et al. 2019). In a well-managed controlled environment, this rapid reproductive rate
is an advantage for generating feedstock for ulvan production.
Asian countries generally contribute a large fraction of global algae production.
Algae are also produced in some countries in Europe and the USA. The FAO data
on global commercial algae production makes no mention of the Ulva species. This
could be classified under “other” (FAO 2018). However, the Ulva green algae are
evidently abundant as they have resulted in algae blooms in areas such as the Yellow
Sea in China off the coast of Jiangsu and Shandong Province (Zhang et al. 2019) and
in Japan at Yatsu tidal flat in Tokyo Bay (Yabe et al. 2009). Green tides in the Yatsu
tidal flat of Tokyo Bay could cover an area of water up to 27.1 ha (0.271 km
2 ) of a
total area of 40 ha (0.4 km
2 ) at peak growth (Yabe et al. 2009). That is over 67% of
the lagoon being covered by green tide. The green tide of the Yellow Sea in China
covers an area of 20,000 km
2 and has been described as the largest ever experienced
in the world (Zhang et al. 2019). Therefore, not only is the ulvan producing green
algae available, they are presently causing environmental nuisance and finding ways
to utilize these green algae is a priority.
8.5 Extraction of Ulvan
As a water-soluble fiber, ulvan can be extracted from green algae using aqueous
extraction. Typical extraction temperature ranges between 80 and 90 °C. An extractant such as ammonium oxalate is often used at a 0.02M concentration (Robic et al.
2009) as a divalent cationic chelating agent to aid the extraction by making the
biomass more susceptible to the solvent. The crude extract can be further purified
using alcohol or quaternary ammonium salt precipitation (Lahaye and Robic 2007;
Shao et al. 2011; Rioux and Turgeon 2015). High-temperature acidic extraction at
a pH of 2 and a temperature of around 80 °C are also used to extract ulvan (Yaich
et al. 2014; Rioux and Turgeon 2015).
8 Ulvans
Unlike brown algae with a relatively complex reproductive cycle which makes
controlled cultivation in aquaculture more labor and cost intensive to be economically viable for commercial biopolymer production, the cultivation of green algae
is relatively simpler. Due to its relatively rapid growth rate and simpler cultivation
process, the ulvan species of green algae are more promising for the cultivation of
monocultures which will result in more uniform ulvan extracts. This is important in
developing standard formulations with specific bioactivities where factors such as
molecular weight and degree of sulfation are within shorter ranges. Some Ulva green
algae grow so easily that in situations where there is an environmental imbalance
in the aquatic ecosystem such as increase in nutrient content of the water this could
result in drastic population boom of green algae resulting in what is known as green
tides (Kidgell et al. 2019). The Ulva species have been identified as one of the algae
species which form algae blooms (Young and Gobler 2016). Ulva prolifera, a highly
productive Ulva can increase by 28% in population within a period of 24 h (Zhang
et al. 2019). In a well-managed controlled environment, this rapid reproductive rate
is an advantage for generating feedstock for ulvan production.
Asian countries generally contribute a large fraction of global algae production.
Algae are also produced in some countries in Europe and the USA. The FAO data
on global commercial algae production makes no mention of the Ulva species. This
could be classified under “other” (FAO 2018). However, the Ulva green algae are
evidently abundant as they have resulted in algae blooms in areas such as the Yellow
Sea in China off the coast of Jiangsu and Shandong Province (Zhang et al. 2019) and
in Japan at Yatsu tidal flat in Tokyo Bay (Yabe et al. 2009). Green tides in the Yatsu
tidal flat of Tokyo Bay could cover an area of water up to 27.1 ha (0.271 km
2 ) of a
total area of 40 ha (0.4 km
2 ) at peak growth (Yabe et al. 2009). That is over 67% of
the lagoon being covered by green tide. The green tide of the Yellow Sea in China
covers an area of 20,000 km
2 and has been described as the largest ever experienced
in the world (Zhang et al. 2019). Therefore, not only is the ulvan producing green
algae available, they are presently causing environmental nuisance and finding ways
to utilize these green algae is a priority.
8.5 Extraction of Ulvan
As a water-soluble fiber, ulvan can be extracted from green algae using aqueous
extraction. Typical extraction temperature ranges between 80 and 90 °C. An extractant such as ammonium oxalate is often used at a 0.02M concentration (Robic et al.
2009) as a divalent cationic chelating agent to aid the extraction by making the
biomass more susceptible to the solvent. The crude extract can be further purified
using alcohol or quaternary ammonium salt precipitation (Lahaye and Robic 2007;
Shao et al. 2011; Rioux and Turgeon 2015). High-temperature acidic extraction at
a pH of 2 and a temperature of around 80 °C are also used to extract ulvan (Yaich
et al. 2014; Rioux and Turgeon 2015).