218
10 Aquatic Plants and Algae Proteins
extraction of protein from red algae (Joubert and Fleurence 2008; Fleurence et al.
1995). One limitation of the enzyme extraction method is the high concentration of
enzymes required to achieve commercially feasible yields. This could be around (48.0
× 10
3 units/100 g) (Bleakley and Hayes 2017). Extraction yields of the enzymatic
method are higher compared to the other conventional methods. Extraction yields of
up to 87% (weight of protein extracted per weight of protein present in the biomass)
have been reported (Harnedy and FitzGerald 2013).
10.5.4 Ultrafiltration and Diafiltration
These processes can be used in combination to optimize the yield and/or quality of
protein extract. For example, in the extraction of water-soluble protein from Nannochloropsis gaditana microalgae, the cell disruption in order to free the proteins
prior to ultrafiltration or diafiltration was carried out with either a combination of
high-pressure homogenization and ultrafiltration/diafiltration or a combination of
enzyme treatment with protease enzyme and ultrafiltration/diafiltration (Safi et al.
2017). This method is presented as a mild biorefinery process which has less environmental impact in terms of minimal use of solvents and acids or alkali. High-pressure
homogenization at 150 GPa permeating at 9 L h
−1 was sufficient to break the cell
walls of the microalgae and release the proteins in the aqueous system. The ultracentrifugation followed by diafiltration was then required to separate the polysaccharides
from the proteins. Although the system was maintained at room temperature with
no additional heat input, due to the frictional forces resulting in heat generation during homogenization, a cooling system was necessary to maintain the temperature at
30 °C. When cell disruption was achieved using enzymatic treatment, this was carried out at a temperature of 50 °C and a pH of 8. The enzyme treatment was allowed
a period of 4 h using alcalase, a protease enzyme.
The combination of enzyme treatment with ultrafiltration and diafiltration resulted
in a higher yield than when high-pressure homogenization was combined with ultrafiltration/diafiltration in the particular study where a yield of 24.8% was obtained for
the former and 17.4% for the latter. This does not necessarily mean that the enzyme
method would always result in a higher yield for all algae; this needs to be carried
out for a range of species and a correlation drawn between yield and species for both
methods before such conclusions can be made. Figure 10.1 shows a flowchart of the
extraction process involving cell disruption, ultrafiltration and diafiltration.
10.5.5 Assisted Extraction
The conventional extraction methods can be modified by using additional techniques
to assist the extraction process. An example is the use of ultrasound. This could be
used to create tiny bubbles within the extraction medium, weather neutral, alkaline
10 Aquatic Plants and Algae Proteins
extraction of protein from red algae (Joubert and Fleurence 2008; Fleurence et al.
1995). One limitation of the enzyme extraction method is the high concentration of
enzymes required to achieve commercially feasible yields. This could be around (48.0
× 10
3 units/100 g) (Bleakley and Hayes 2017). Extraction yields of the enzymatic
method are higher compared to the other conventional methods. Extraction yields of
up to 87% (weight of protein extracted per weight of protein present in the biomass)
have been reported (Harnedy and FitzGerald 2013).
10.5.4 Ultrafiltration and Diafiltration
These processes can be used in combination to optimize the yield and/or quality of
protein extract. For example, in the extraction of water-soluble protein from Nannochloropsis gaditana microalgae, the cell disruption in order to free the proteins
prior to ultrafiltration or diafiltration was carried out with either a combination of
high-pressure homogenization and ultrafiltration/diafiltration or a combination of
enzyme treatment with protease enzyme and ultrafiltration/diafiltration (Safi et al.
2017). This method is presented as a mild biorefinery process which has less environmental impact in terms of minimal use of solvents and acids or alkali. High-pressure
homogenization at 150 GPa permeating at 9 L h
−1 was sufficient to break the cell
walls of the microalgae and release the proteins in the aqueous system. The ultracentrifugation followed by diafiltration was then required to separate the polysaccharides
from the proteins. Although the system was maintained at room temperature with
no additional heat input, due to the frictional forces resulting in heat generation during homogenization, a cooling system was necessary to maintain the temperature at
30 °C. When cell disruption was achieved using enzymatic treatment, this was carried out at a temperature of 50 °C and a pH of 8. The enzyme treatment was allowed
a period of 4 h using alcalase, a protease enzyme.
The combination of enzyme treatment with ultrafiltration and diafiltration resulted
in a higher yield than when high-pressure homogenization was combined with ultrafiltration/diafiltration in the particular study where a yield of 24.8% was obtained for
the former and 17.4% for the latter. This does not necessarily mean that the enzyme
method would always result in a higher yield for all algae; this needs to be carried
out for a range of species and a correlation drawn between yield and species for both
methods before such conclusions can be made. Figure 10.1 shows a flowchart of the
extraction process involving cell disruption, ultrafiltration and diafiltration.
10.5.5 Assisted Extraction
The conventional extraction methods can be modified by using additional techniques
to assist the extraction process. An example is the use of ultrasound. This could be
used to create tiny bubbles within the extraction medium, weather neutral, alkaline