74
4 Alginates
production with Norway leading the production in Europe at 154,230 tonnes of brown
seaweed harvested from natural stock annually. France harvested 33,919 tonnes wild
seaweed in the same year (Monagail et al. 2017). Therefore, although aquaculture
has become more dominant, wild seaweed still plays a significant role, and however,
these are more economical sold as food for direct consumption rather than as sources
for alginate. 800,000 tonnes of wild seaweed has been recorded in 2014 from a total
of 32 countries. Compared to, as of 2003, 35–42 countries, out of the 195 countries
in the world were reported to be involved in seaweed production (McHugh 2003). As
of 2016, FAO reports 30.1 million tonnes of farmed aquatic plants globally, a large
proportion of this being seaweeds and smaller proportion of microalgae.
It can therefore be concluded that a smaller proportion of the seaweed available
is diverted to alginate production while a larger proportion is used for food as has
been for centuries. This is mainly due to the need for the alginophytes to be sourced
from natural stock. Nonetheless, the alginate market is thriving on brown seaweed
production in the hundred thousand tonnes which presently meets the global demand
estimated at an annual rate of 26,500 MT (Konda et al. 2015).
4.5 Extraction of Alginates
First Isolated by Dr E. C. C Stanford in 1881 in Britain (Draget 2009; Parreidt
et al. 2018), alginate makes up about 10–45% of the dry mass of seaweed (Chen and
Long 2018). Extraction yield of alginate reported ranges from 16.93% from Padina to
30.3% from S. crassifolium (Mushollaeni 2011). Commercially chemical extraction
methods are more widely used in industries. Novel methods are being explored by
researchers which are more cost-effective and also more environmentally friendly.
This includes the use of enzymes such as alginate lyase (Chen and Long 2018).
Alginate is often extracted as sodium alginate or in other forms such as calcium
alginate. These are explored separately in the following subsections.
4.5.1 Extraction of Sodium Alginate
Within the cell walls of brown algae, alginate occurs as salts of alginic acid as calcium,
magnesium and sodium alginic acid salts. Sodium alginate is mostly extracted since
it is the only water-soluble salt of alginic acid. It is therefore of more economic
significance. This solubility in water makes it more practical to extract and also
apply. The extraction process involves isolating the sodium alginate by dissolving it
out in water. The other alginates (calcium and magnesium) must also be converted
to sodium alginates in order to have a good yield of alginate from the source. Three
methods of extractions are outlined as follows. In all three methods, the seaweed is
first prepared by washing, cutting or milling to reduce size and the pigments removed.
Removal of pigment can be achieved with formaldehyde, and the cell walls may be
4 Alginates
production with Norway leading the production in Europe at 154,230 tonnes of brown
seaweed harvested from natural stock annually. France harvested 33,919 tonnes wild
seaweed in the same year (Monagail et al. 2017). Therefore, although aquaculture
has become more dominant, wild seaweed still plays a significant role, and however,
these are more economical sold as food for direct consumption rather than as sources
for alginate. 800,000 tonnes of wild seaweed has been recorded in 2014 from a total
of 32 countries. Compared to, as of 2003, 35–42 countries, out of the 195 countries
in the world were reported to be involved in seaweed production (McHugh 2003). As
of 2016, FAO reports 30.1 million tonnes of farmed aquatic plants globally, a large
proportion of this being seaweeds and smaller proportion of microalgae.
It can therefore be concluded that a smaller proportion of the seaweed available
is diverted to alginate production while a larger proportion is used for food as has
been for centuries. This is mainly due to the need for the alginophytes to be sourced
from natural stock. Nonetheless, the alginate market is thriving on brown seaweed
production in the hundred thousand tonnes which presently meets the global demand
estimated at an annual rate of 26,500 MT (Konda et al. 2015).
4.5 Extraction of Alginates
First Isolated by Dr E. C. C Stanford in 1881 in Britain (Draget 2009; Parreidt
et al. 2018), alginate makes up about 10–45% of the dry mass of seaweed (Chen and
Long 2018). Extraction yield of alginate reported ranges from 16.93% from Padina to
30.3% from S. crassifolium (Mushollaeni 2011). Commercially chemical extraction
methods are more widely used in industries. Novel methods are being explored by
researchers which are more cost-effective and also more environmentally friendly.
This includes the use of enzymes such as alginate lyase (Chen and Long 2018).
Alginate is often extracted as sodium alginate or in other forms such as calcium
alginate. These are explored separately in the following subsections.
4.5.1 Extraction of Sodium Alginate
Within the cell walls of brown algae, alginate occurs as salts of alginic acid as calcium,
magnesium and sodium alginic acid salts. Sodium alginate is mostly extracted since
it is the only water-soluble salt of alginic acid. It is therefore of more economic
significance. This solubility in water makes it more practical to extract and also
apply. The extraction process involves isolating the sodium alginate by dissolving it
out in water. The other alginates (calcium and magnesium) must also be converted
to sodium alginates in order to have a good yield of alginate from the source. Three
methods of extractions are outlined as follows. In all three methods, the seaweed is
first prepared by washing, cutting or milling to reduce size and the pigments removed.
Removal of pigment can be achieved with formaldehyde, and the cell walls may be