10.5 Extraction of Proteins from Algae and Aquatic Plants
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minimal concentration of minerals in the water and optimize concentration gradient
and consequently osmotic pressure. Using this method to extract both water-soluble
and insoluble proteins from Palmaria palmata, one study reports a yields of 0.0677%
for the osmotic method and a yield of 0.0692% (mass protein per dry weight of algae)
using shear force (Harnedy and FitzGerald 2013). Extraction yield of up to 40% has
been reported using the physical method (Harnedy and FitzGerald 2013).
10.5.2 Chemical Extraction
This method requires the use of an alkali or acidic solution for extraction of the
protein. The protein becomes soluble at altered pH and in some cases elevated temperatures. This is likely to obtain the protein in a denatured form. Yields of up to
59% can be obtained using this method (Barbarino and Lourenço 2005). The alkali
or acid could also be used to disrupt the cell wall structure, allowing the protein
to be released more easily. Sodium hydroxide and hydrochloric acid are commonly
used; others include polyethylene glycol, potassium carbonate and N-acetyl-cysteine
(Bleakley and Hayes 2017).
In some cases, the protein can be extracted alongside other components which can
be used alongside the protein, for example, as animal feed. In this case, the processor
can eliminate the cost of separating the protein from these components and simply
needs to obtain the protein from the biomass. An example of this is extraction of leaf
protein concentrate from the water hyacinth. Here the extraction of the leaf protein
concentrate was carried out by first blanching the washed water hyacinth leaves for
5 min with acetic acid at 5% concentration. The blanched leaves where then rinsed
with deionized water to get rid of the acids on the surface after which the biomass was
dried. The next step is to extract the fats, and this was done by soaking in 95% ethanol
within which the fat is soluble. This process was allowed 6 h to allow the alcohol
penetrate into the walls and dissolve the fats and other ethanol-soluble compounds.
This leaves behind the carbohydrates, proteins, minerals and other compounds such
as alkaloids and phenolic compounds. The residual fat in the leap protein concentrate
depends on the yield of extraction. This concentrate can then be used as a protein
source in applications such as animal feed.
10.5.3 Enzyme Extraction
Another way to extract proteins from the algal biomass is through the use of enzymes.
The role of the enzyme is to breakdown the polysaccharides to sugar units which are
soluble and separating the protein. The water-soluble proteins can be separated from
the water-soluble sugars by separation method such as precipitation of the protein
or crystallization of sugars. The enzymes used depend on the type of algae and its
components. Enzymes such as carrageenase, xylanase and cellulase are used for
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minimal concentration of minerals in the water and optimize concentration gradient
and consequently osmotic pressure. Using this method to extract both water-soluble
and insoluble proteins from Palmaria palmata, one study reports a yields of 0.0677%
for the osmotic method and a yield of 0.0692% (mass protein per dry weight of algae)
using shear force (Harnedy and FitzGerald 2013). Extraction yield of up to 40% has
been reported using the physical method (Harnedy and FitzGerald 2013).
10.5.2 Chemical Extraction
This method requires the use of an alkali or acidic solution for extraction of the
protein. The protein becomes soluble at altered pH and in some cases elevated temperatures. This is likely to obtain the protein in a denatured form. Yields of up to
59% can be obtained using this method (Barbarino and Lourenço 2005). The alkali
or acid could also be used to disrupt the cell wall structure, allowing the protein
to be released more easily. Sodium hydroxide and hydrochloric acid are commonly
used; others include polyethylene glycol, potassium carbonate and N-acetyl-cysteine
(Bleakley and Hayes 2017).
In some cases, the protein can be extracted alongside other components which can
be used alongside the protein, for example, as animal feed. In this case, the processor
can eliminate the cost of separating the protein from these components and simply
needs to obtain the protein from the biomass. An example of this is extraction of leaf
protein concentrate from the water hyacinth. Here the extraction of the leaf protein
concentrate was carried out by first blanching the washed water hyacinth leaves for
5 min with acetic acid at 5% concentration. The blanched leaves where then rinsed
with deionized water to get rid of the acids on the surface after which the biomass was
dried. The next step is to extract the fats, and this was done by soaking in 95% ethanol
within which the fat is soluble. This process was allowed 6 h to allow the alcohol
penetrate into the walls and dissolve the fats and other ethanol-soluble compounds.
This leaves behind the carbohydrates, proteins, minerals and other compounds such
as alkaloids and phenolic compounds. The residual fat in the leap protein concentrate
depends on the yield of extraction. This concentrate can then be used as a protein
source in applications such as animal feed.
10.5.3 Enzyme Extraction
Another way to extract proteins from the algal biomass is through the use of enzymes.
The role of the enzyme is to breakdown the polysaccharides to sugar units which are
soluble and separating the protein. The water-soluble proteins can be separated from
the water-soluble sugars by separation method such as precipitation of the protein
or crystallization of sugars. The enzymes used depend on the type of algae and its
components. Enzymes such as carrageenase, xylanase and cellulase are used for