13.2 Occurrence in Nature
289
For example, marine red microalgae, Porphyridium marinum, grow optimally at a
light intensity of 100 µmol photons m
−2 s
−1 , sodium nitrate (NaNO 3 ) concentration
of 1 g/L and a sodium chloride concentration of 20 g/l (Himaa et al. 2019). At this
optimal condition, these algae can accumulate up to 140.21 µg per ml which is 13%
higher than when grown in suboptimal conditions. The lower the light intensity and
salinity, the higher the starch accumulated within the microalgae.
Starch is also present in a considerable amount in aquatic plants such as water
hyacinth and duckweed. The composition of starch in aquatic plants varies from
species to species and is also affected by seasonal variation and growth conditions.
In Azolla, for example, filiculoides produces up to 36.4 g/L more sugars than another
strain of Azolla pinnata. Filiculoides biomass contains 6.05% starch while pinnata
contains 4.7%. Pinnata also has higher lignin content (Miranda et al. 2016). Azolla,
in general, has the highest lignin content of all the common aquatic plants explored
in the literature; however, this lignin content (13.2% for pinnata and 10.3% for
filiculoides) is still lower than those of terrestrial lignocellulose crops such as corn
and sugar beets.
In algae, the location of starch on the organism could vary. The starch could be
present in the chloroplast, cytoplasm or pyrenoids. They could also be present in the
form of plates or granules. For example, in the red algae Gracilariopsis, starch is
present in the form of granules within the cytoplasm; in the green algae Cladophora,
starch is present within the chloroplasts in form of granules; and in the green algae
ulva, starch is present in the form of plates around the pyrenoids and as granules in
the chloroplast thylakoid membranes.
Starch content could vary depending on the environmental conditions. Growing
in the open environment weather conditions significantly affect the starch content at
any period. Starch content also varies with the organism’s reproductive cycle. Studies
on the green algae Ulva ohnois indicated a minimal starch accumulation at the initial
growth phase; in the particular study, this occured between March and May and
maximum starch content was recorded in June. Note that the biomass accumulation
rate does not necessarily correlate with the starch accumulation rate. A faster growth
rate is not necessarily implicative of a higher starch content, and the organism could
be accumulating other compounds such as cellulose, proteins and lipids.
There are also instances where starch is degraded into other polymers within the
aquatic organism, and this has been observed in red algae. Degradation of starch
into carrageenan was observed in S. cordalis, a unicellular red algae. It appears that
under various conditions such as nutrient supply and irradiance, and the starch within
the organism is converted into carrageenan (Fournet et al. 2000). This is attributed
to the need for the organism to switch to a biochemical pathway which favors the
surrounding condition. Starch also exists in the aquatic environment in the form of
floridean starch (Himaa et al. 2019). This refers to starch sourced from a particular
strain of red algae known as the florideophyceae. It is mainly characterized by the
absence of the branched polymer of starch, amylopectin. Floridean starch is discussed
in more detail in a separate section within this chapter.
289
For example, marine red microalgae, Porphyridium marinum, grow optimally at a
light intensity of 100 µmol photons m
−2 s
−1 , sodium nitrate (NaNO 3 ) concentration
of 1 g/L and a sodium chloride concentration of 20 g/l (Himaa et al. 2019). At this
optimal condition, these algae can accumulate up to 140.21 µg per ml which is 13%
higher than when grown in suboptimal conditions. The lower the light intensity and
salinity, the higher the starch accumulated within the microalgae.
Starch is also present in a considerable amount in aquatic plants such as water
hyacinth and duckweed. The composition of starch in aquatic plants varies from
species to species and is also affected by seasonal variation and growth conditions.
In Azolla, for example, filiculoides produces up to 36.4 g/L more sugars than another
strain of Azolla pinnata. Filiculoides biomass contains 6.05% starch while pinnata
contains 4.7%. Pinnata also has higher lignin content (Miranda et al. 2016). Azolla,
in general, has the highest lignin content of all the common aquatic plants explored
in the literature; however, this lignin content (13.2% for pinnata and 10.3% for
filiculoides) is still lower than those of terrestrial lignocellulose crops such as corn
and sugar beets.
In algae, the location of starch on the organism could vary. The starch could be
present in the chloroplast, cytoplasm or pyrenoids. They could also be present in the
form of plates or granules. For example, in the red algae Gracilariopsis, starch is
present in the form of granules within the cytoplasm; in the green algae Cladophora,
starch is present within the chloroplasts in form of granules; and in the green algae
ulva, starch is present in the form of plates around the pyrenoids and as granules in
the chloroplast thylakoid membranes.
Starch content could vary depending on the environmental conditions. Growing
in the open environment weather conditions significantly affect the starch content at
any period. Starch content also varies with the organism’s reproductive cycle. Studies
on the green algae Ulva ohnois indicated a minimal starch accumulation at the initial
growth phase; in the particular study, this occured between March and May and
maximum starch content was recorded in June. Note that the biomass accumulation
rate does not necessarily correlate with the starch accumulation rate. A faster growth
rate is not necessarily implicative of a higher starch content, and the organism could
be accumulating other compounds such as cellulose, proteins and lipids.
There are also instances where starch is degraded into other polymers within the
aquatic organism, and this has been observed in red algae. Degradation of starch
into carrageenan was observed in S. cordalis, a unicellular red algae. It appears that
under various conditions such as nutrient supply and irradiance, and the starch within
the organism is converted into carrageenan (Fournet et al. 2000). This is attributed
to the need for the organism to switch to a biochemical pathway which favors the
surrounding condition. Starch also exists in the aquatic environment in the form of
floridean starch (Himaa et al. 2019). This refers to starch sourced from a particular
strain of red algae known as the florideophyceae. It is mainly characterized by the
absence of the branched polymer of starch, amylopectin. Floridean starch is discussed
in more detail in a separate section within this chapter.