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5 Fucoidan
5.5.1 Acid Extraction
The use of acid for extraction of fucoidan is the oldest known method. This involves
solubilizing the fucoidan in an aqueous acid solution at high temperature. This is then
followed by precipitation of the dissolved fucoidan with ethanol. This process is based
on the fact that fucoidan is soluble in polar liquids at low pH and elevated temperature
but insoluble in less polar solvents. Subsequent solubilization and precipitation can
then be carried to further purify the extracted fucoidan (Fitton et al. 2015a, b). The
proteins and alginate within the algae or sea cucumber will also be dissolved at
low pH and high temperature. The alginates can be separated from the fucoidan by
precipitation.
An example process is as follows (Sinurat et al. 2015; Lu et al. 2018): The brown
seaweeds are first soaked in a mixture of methanol, chloroform and water in the ratio
4:2:1 over a duration of 12 h. This process removes the fats and depigments the brown
algae. This is then followed by washing in acetone, and the defatted and depigmented
algae are then air-dried. The dried biomass is then treated with 0.01M HCl at a pH
of 4 with a weight-to-volume ratio of 1:10 (g:ml) under continuous stirring for 6 h.
The liquid extract obtained after filtering contains fucoidan as well as acid-soluble
proteins, alginates and smaller particles which get through the filter pore space. The
alginate is separated by precipitation with 4M of calcium chloride (CaCl 2 ) under
incubation for a period of 30 min after which the precipitates are filtered off. The
precipitation is repeated to further remove more alginates. This is then followed by
centrifugation at 1544 g for 15 min in order to remove the smaller particles. Crude
fucoidan is then obtained from the solution by precipitation with ethanol and further
purified by dialysis at a cutoff point of 10 kDa. This process is based on method
reported for research studies which can also be scaled up for industrial fucoidan
production. A flowchart of the extraction process is provided in Fig. 5.2.
5.5.2 Enzyme Extraction
Here an example extraction process of extraction of fucoidan from sea cucumber
is used to explain the enzyme-based extraction of fucoidan. The enzyme extraction
process involves breaking down of the proteins in the tissue using papain. The body
of the sea cucumber which can be purchased from fishermen or from the market is
dried and milled into smaller particle sizes. The pH is adjusted using hydrochloric
acid, and the papain is added at a concentration of 0.15%. The extraction is carried out
at 50 °C for a period of 2 h at a ph of 6 and a solid-to-liquid ratio of 1 g:16.26 mL—
based on optimum conditions reported by Qin et al. (2018). This process results in the
breaking down of the tissue proteins into peptides. The pH is then adjusted to a lower
pH of 2.8 at a temperature of 4 °C over a period of 4 h. This allows the acidic proteins
to be removed and separated by centrifugation (7441 × g for 20 min). The liquid
supernatant obtained after the centrifugation contains a mixture of compounds. The
5 Fucoidan
5.5.1 Acid Extraction
The use of acid for extraction of fucoidan is the oldest known method. This involves
solubilizing the fucoidan in an aqueous acid solution at high temperature. This is then
followed by precipitation of the dissolved fucoidan with ethanol. This process is based
on the fact that fucoidan is soluble in polar liquids at low pH and elevated temperature
but insoluble in less polar solvents. Subsequent solubilization and precipitation can
then be carried to further purify the extracted fucoidan (Fitton et al. 2015a, b). The
proteins and alginate within the algae or sea cucumber will also be dissolved at
low pH and high temperature. The alginates can be separated from the fucoidan by
precipitation.
An example process is as follows (Sinurat et al. 2015; Lu et al. 2018): The brown
seaweeds are first soaked in a mixture of methanol, chloroform and water in the ratio
4:2:1 over a duration of 12 h. This process removes the fats and depigments the brown
algae. This is then followed by washing in acetone, and the defatted and depigmented
algae are then air-dried. The dried biomass is then treated with 0.01M HCl at a pH
of 4 with a weight-to-volume ratio of 1:10 (g:ml) under continuous stirring for 6 h.
The liquid extract obtained after filtering contains fucoidan as well as acid-soluble
proteins, alginates and smaller particles which get through the filter pore space. The
alginate is separated by precipitation with 4M of calcium chloride (CaCl 2 ) under
incubation for a period of 30 min after which the precipitates are filtered off. The
precipitation is repeated to further remove more alginates. This is then followed by
centrifugation at 1544 g for 15 min in order to remove the smaller particles. Crude
fucoidan is then obtained from the solution by precipitation with ethanol and further
purified by dialysis at a cutoff point of 10 kDa. This process is based on method
reported for research studies which can also be scaled up for industrial fucoidan
production. A flowchart of the extraction process is provided in Fig. 5.2.
5.5.2 Enzyme Extraction
Here an example extraction process of extraction of fucoidan from sea cucumber
is used to explain the enzyme-based extraction of fucoidan. The enzyme extraction
process involves breaking down of the proteins in the tissue using papain. The body
of the sea cucumber which can be purchased from fishermen or from the market is
dried and milled into smaller particle sizes. The pH is adjusted using hydrochloric
acid, and the papain is added at a concentration of 0.15%. The extraction is carried out
at 50 °C for a period of 2 h at a ph of 6 and a solid-to-liquid ratio of 1 g:16.26 mL—
based on optimum conditions reported by Qin et al. (2018). This process results in the
breaking down of the tissue proteins into peptides. The pH is then adjusted to a lower
pH of 2.8 at a temperature of 4 °C over a period of 4 h. This allows the acidic proteins
to be removed and separated by centrifugation (7441 × g for 20 min). The liquid
supernatant obtained after the centrifugation contains a mixture of compounds. The