4.5 Extraction of Alginates
77
then follows as outlined in method 2. If the acid method is used, alginic acid formed
is gelatinous and cannot be separated by filtration, and flotation is used in this case.
The gelatinous alginic acid is then dewatered followed by reconversion to sodium
alginate as outlined in method 1.
The color of the sodium alginate extract is very important in enhancing or diminishing its market value. Lighter colored alginate attracts better price. This necessitates
a decoloring process either before or after the alkali treatment. Decoloring can be
achieved by either bleaching the final product with sodium hypochlorite to remove
color or soaking the seaweed in formalin prior to extraction in order to adhere the
pigment to the cellulose such that the pigment is retained in the cellulose while the
sodium alginate is extracted.
4.5.5 Extraction of Calcium Alginate and Other Salts
of Alginic Acid
The process of extracting sodium alginate also involves formation of calcium alginate, and therefore, if calcium alginate is the desired product, following the initial
treatment of the seaweed with hot sodium carbonate, the calcium salt route of method
1 can be taken (McHugh 1987). Addition of calcium salt such as calcium chloride
will result in the formation of calcium alginate which is an insoluble fibrous alginate
that can be separated by filtration. Although sodium alginate is more widely produced, calcium alginate finds increasing applications in food and pharmaceuticals.
The other salts of alginate are obtained following neutralization of alginic acid using
alkali like potassium carbonate and ammonium hydroxide. The alkali used depends
on the desired salt.
However, propylene glycol alginate is made in a different way. It is an ester of
alginic acid, and its application varies from that of the alginate salts. The process of
producing propylene glycol alginate begins from the moist alginic acid which has
partially reacted with sodium carbonate. This partially reacted alginic acid is then
treated with propylene oxide at a temperature of 80 °C for two hours under pressure.
4.5.6 Enzyme Extraction of Alginate
Although the chemical extraction method is almost the only method used in commercial production of alginate, other methods of extraction are possible greener
alternatives to obtain alginates. For such process, alginate lyases can be employed,
and however, these alginate degrading enzymes are primarily used in breaking down
the alginate chains into oligosaccharides of alginate, mannuronic and guluronic acids
(Rhein-Knudsen et al. 2015). These have been shown to have some bioactive properties and show potential for applications in biomedicine and biofuel production. The
77
then follows as outlined in method 2. If the acid method is used, alginic acid formed
is gelatinous and cannot be separated by filtration, and flotation is used in this case.
The gelatinous alginic acid is then dewatered followed by reconversion to sodium
alginate as outlined in method 1.
The color of the sodium alginate extract is very important in enhancing or diminishing its market value. Lighter colored alginate attracts better price. This necessitates
a decoloring process either before or after the alkali treatment. Decoloring can be
achieved by either bleaching the final product with sodium hypochlorite to remove
color or soaking the seaweed in formalin prior to extraction in order to adhere the
pigment to the cellulose such that the pigment is retained in the cellulose while the
sodium alginate is extracted.
4.5.5 Extraction of Calcium Alginate and Other Salts
of Alginic Acid
The process of extracting sodium alginate also involves formation of calcium alginate, and therefore, if calcium alginate is the desired product, following the initial
treatment of the seaweed with hot sodium carbonate, the calcium salt route of method
1 can be taken (McHugh 1987). Addition of calcium salt such as calcium chloride
will result in the formation of calcium alginate which is an insoluble fibrous alginate
that can be separated by filtration. Although sodium alginate is more widely produced, calcium alginate finds increasing applications in food and pharmaceuticals.
The other salts of alginate are obtained following neutralization of alginic acid using
alkali like potassium carbonate and ammonium hydroxide. The alkali used depends
on the desired salt.
However, propylene glycol alginate is made in a different way. It is an ester of
alginic acid, and its application varies from that of the alginate salts. The process of
producing propylene glycol alginate begins from the moist alginic acid which has
partially reacted with sodium carbonate. This partially reacted alginic acid is then
treated with propylene oxide at a temperature of 80 °C for two hours under pressure.
4.5.6 Enzyme Extraction of Alginate
Although the chemical extraction method is almost the only method used in commercial production of alginate, other methods of extraction are possible greener
alternatives to obtain alginates. For such process, alginate lyases can be employed,
and however, these alginate degrading enzymes are primarily used in breaking down
the alginate chains into oligosaccharides of alginate, mannuronic and guluronic acids
(Rhein-Knudsen et al. 2015). These have been shown to have some bioactive properties and show potential for applications in biomedicine and biofuel production. The