294
13 Starch
presented various starch conformations which included ovoid, spherical and pearshaped starch granules as well as irregularly shaped ones. The pyrenoids were also
found to be surrounded by starch plates (Prabhu et al. 2019). This orientation of starch
within these particular algae does not deviate from that of similar starch-containing
terrestrial plants.
Hydrolysis occurs more readily in gelatinized starch than in the native granular
starch form. This can be explained by the increased surface area of the chain as they
interact with water to form temporary network structures in the gelatinized form,
thus leaving the polymer chains more vulnerable to degradation. Hydrolysis can be
carried out using acids or enzymes. Amylase and amyloglucosidase are enzymes
used for enzymatic hydrolysis of starch. Enzymatic hydrolysis is preferred as the
enzymes are selective, and they break only the amylose and amylopectin glycosidic
bonds. However, the acid hydrolysis is non-selective and breaks all the glycosidic
bonds within the biomass. For applications, such as bioethanol production acid,
hydrolysis of all the carbohydrates is desirable; however, for more selective processes
or analysis, enzyme hydrolysis is preferred. Studies on aquatic-sourced starch such
as that from U. ohnois macroalgae (Prabhu et al. 2019) have shown that aquatic
starches are susceptible to enzymatic and acidic hydrolysis as terrestrial plant-sourced
starches. For example, high-performance ion chromatograms of starch from the green
algae U. ohnois showing major peak indicating the presence of main glucose in the
acid- and enzyme-hydrolyzed starch extracts confirm that starch from such source can
be hydrolyzed to form glucose. The susceptibility to hydrolysis is an important step
toward determining the suitability of algal starch for human or animal consumption
and for other applications.
Granule size is an important characteristic of starch. It affects properties such as
gelatinization temperature, efficiency of hydrolysis and crystallinity. Gelatinization
temperature of different sources of starch is due to the variation in the amylose and
amylopectin content and the size of the starch granules. For instance, the starch granules of the green algae U. ohnois are smaller than those of potato starch, resulting in a
higher gelatinization temperature of potato starch. Starch from microalgae Chlorella
sorokiniana has granule size of 1 µm. In addition to this, its molecular weight, A
type crystallinity pattern (crystallinity 30%) as well as amylose content is similar to
starch from cereal plants (Gifuni et al. 2017). When SEM images of starch granules
extracted from aquatic plant U. ohnoi were compared, the surfaces of the algal starch
appeared smoother compared to that of the potato-sourced starch. Typical size of
red macroalgae starch granule is ~2 to 5 µm (Yu et al. 2002) that of U. ohnoi was
observed to range an average of 6.6 µm with a relatively large standard deviation
as the granule sizes ranged from 0.7 to 27.4 µm with multiple peaks in the size
distribution characterization. Although the size of U. ohnoi starch granules is larger
than that of typical red macroalgae, this variation in the size distribution of starch
granules within species of aquatic plants is not too far from those of other typical
terrestrial-sourced starch. For instance, potato starch granules have an average size
of 45.5 µm while those of rice starch are between 2 and 7 µm (Le Corre and Brass
2010). This implies that the applicability of starch extracted from aquatic source is
not limited by the granule size. Although the cause of this variation in starch granule
13 Starch
presented various starch conformations which included ovoid, spherical and pearshaped starch granules as well as irregularly shaped ones. The pyrenoids were also
found to be surrounded by starch plates (Prabhu et al. 2019). This orientation of starch
within these particular algae does not deviate from that of similar starch-containing
terrestrial plants.
Hydrolysis occurs more readily in gelatinized starch than in the native granular
starch form. This can be explained by the increased surface area of the chain as they
interact with water to form temporary network structures in the gelatinized form,
thus leaving the polymer chains more vulnerable to degradation. Hydrolysis can be
carried out using acids or enzymes. Amylase and amyloglucosidase are enzymes
used for enzymatic hydrolysis of starch. Enzymatic hydrolysis is preferred as the
enzymes are selective, and they break only the amylose and amylopectin glycosidic
bonds. However, the acid hydrolysis is non-selective and breaks all the glycosidic
bonds within the biomass. For applications, such as bioethanol production acid,
hydrolysis of all the carbohydrates is desirable; however, for more selective processes
or analysis, enzyme hydrolysis is preferred. Studies on aquatic-sourced starch such
as that from U. ohnois macroalgae (Prabhu et al. 2019) have shown that aquatic
starches are susceptible to enzymatic and acidic hydrolysis as terrestrial plant-sourced
starches. For example, high-performance ion chromatograms of starch from the green
algae U. ohnois showing major peak indicating the presence of main glucose in the
acid- and enzyme-hydrolyzed starch extracts confirm that starch from such source can
be hydrolyzed to form glucose. The susceptibility to hydrolysis is an important step
toward determining the suitability of algal starch for human or animal consumption
and for other applications.
Granule size is an important characteristic of starch. It affects properties such as
gelatinization temperature, efficiency of hydrolysis and crystallinity. Gelatinization
temperature of different sources of starch is due to the variation in the amylose and
amylopectin content and the size of the starch granules. For instance, the starch granules of the green algae U. ohnois are smaller than those of potato starch, resulting in a
higher gelatinization temperature of potato starch. Starch from microalgae Chlorella
sorokiniana has granule size of 1 µm. In addition to this, its molecular weight, A
type crystallinity pattern (crystallinity 30%) as well as amylose content is similar to
starch from cereal plants (Gifuni et al. 2017). When SEM images of starch granules
extracted from aquatic plant U. ohnoi were compared, the surfaces of the algal starch
appeared smoother compared to that of the potato-sourced starch. Typical size of
red macroalgae starch granule is ~2 to 5 µm (Yu et al. 2002) that of U. ohnoi was
observed to range an average of 6.6 µm with a relatively large standard deviation
as the granule sizes ranged from 0.7 to 27.4 µm with multiple peaks in the size
distribution characterization. Although the size of U. ohnoi starch granules is larger
than that of typical red macroalgae, this variation in the size distribution of starch
granules within species of aquatic plants is not too far from those of other typical
terrestrial-sourced starch. For instance, potato starch granules have an average size
of 45.5 µm while those of rice starch are between 2 and 7 µm (Le Corre and Brass
2010). This implies that the applicability of starch extracted from aquatic source is
not limited by the granule size. Although the cause of this variation in starch granule