8.5 Extraction of Ulvan
175
Here, the extraction method used by Tabarsa et al. (2018) to extract ulvan from
Ulva intestinalis is used as an example of extraction process. Algae strain U. intestinalis were sourced from the Iranian coast, Noor. The collected biomass was then
washed using tap water followed by drying at a temperature of 60 °C. To reduce
the particle size, the washed and dried algae mass was ground using a blender and
sieved to particle size below 0.5 mm. To isolate crude polysaccharide, the alcoholsoluble pigments, lipids and low molecular weight compounds were removed from
the ground seaweed by adding 80% ethanol at a mass-to-volume ratio of 1:10 (g:mL).
This was left overnight at ambient conditions. Separation was carried out using a centrifuge at 10 °C at 8000 rpm for 10 min followed by decanting off of the supernatant.
The solid residue which now contains a mix of polysaccharides and other macromolecules is then rinsed with acetone and dried at room temperature. The next stage
which involved extraction of the water-soluble polysaccharides was carried out at
65 °C using distilled water in the mass-to-volume ratio of 1: 20 (g:ml). The extraction time allowed in the particular study was 2 h. Following the extraction period,
the liquid extract was separated from the solid residue using centrifugation at 10 °C
operating at 10,000 rpm for 10 min. The extraction was repeated with fresh distilled water to further remove soluble sulphated polysaccharides. The extracts from
both runs were combined and evaporated under reduced pressure at a temperature
of 60 °C. The ulvan was precipitated out using 90% ethanol (when added to liquid
mixture concentration of ethanol decreases to 70%). Precipitation was allowed to
take place overnight at 4 °C followed by centrifugation at 10,000 rpm for 10 min at
10 °C. The precipitated were further washed and dehydrated with acetone and 99%
ethanol, respectively. The final product was dried at room temperature.
Following extraction of the crude ulvan, it is often desired to separate into different fractions. This could be for analysis or obtaining a less polydisperse product.
The bioactivity of ulvans like other polysaccharides is affected by the molecular
weight. Therefore, separating into fractions with specific range of molecular weight
is important in analyzing and utilizing these bioactivities and physicochemical properties. Fractionation can be carried out using methods such as DEAE-Sepharose Fast
Flow column (Tabarsa et al. 2018).
Co-extraction can be carried out to extract other polymers alongside the ulvan
since the cell walls always contain other useful polysaccharides such as cellulose,
xyloglucans as well as proteins. This would then involve including a separation
process after the extraction stage. The yield and quality of ulvan obtained from
any given biomass depend on the conditions of extraction. Temperature, pH, use
of extractants and concentration of extractant, particle size of biomass, duration of
extraction and pretreatment method are factors which have been identified to affect
the yield and quality of ulvan extraction (Kidgell et al. 2019). The yield is defined
in terms of the quantity of actual extract compared to the known content of ulvan in
the biomass, while the quality is quantified by the degree of polymerization; hence,
molecular weight of the ulvan extracted the purity (i.e., absence of other polymers
and contaminants) and the level of degradation as a result of depolymerization and
desulphurization of the ulvan in the process of extraction.
175
Here, the extraction method used by Tabarsa et al. (2018) to extract ulvan from
Ulva intestinalis is used as an example of extraction process. Algae strain U. intestinalis were sourced from the Iranian coast, Noor. The collected biomass was then
washed using tap water followed by drying at a temperature of 60 °C. To reduce
the particle size, the washed and dried algae mass was ground using a blender and
sieved to particle size below 0.5 mm. To isolate crude polysaccharide, the alcoholsoluble pigments, lipids and low molecular weight compounds were removed from
the ground seaweed by adding 80% ethanol at a mass-to-volume ratio of 1:10 (g:mL).
This was left overnight at ambient conditions. Separation was carried out using a centrifuge at 10 °C at 8000 rpm for 10 min followed by decanting off of the supernatant.
The solid residue which now contains a mix of polysaccharides and other macromolecules is then rinsed with acetone and dried at room temperature. The next stage
which involved extraction of the water-soluble polysaccharides was carried out at
65 °C using distilled water in the mass-to-volume ratio of 1: 20 (g:ml). The extraction time allowed in the particular study was 2 h. Following the extraction period,
the liquid extract was separated from the solid residue using centrifugation at 10 °C
operating at 10,000 rpm for 10 min. The extraction was repeated with fresh distilled water to further remove soluble sulphated polysaccharides. The extracts from
both runs were combined and evaporated under reduced pressure at a temperature
of 60 °C. The ulvan was precipitated out using 90% ethanol (when added to liquid
mixture concentration of ethanol decreases to 70%). Precipitation was allowed to
take place overnight at 4 °C followed by centrifugation at 10,000 rpm for 10 min at
10 °C. The precipitated were further washed and dehydrated with acetone and 99%
ethanol, respectively. The final product was dried at room temperature.
Following extraction of the crude ulvan, it is often desired to separate into different fractions. This could be for analysis or obtaining a less polydisperse product.
The bioactivity of ulvans like other polysaccharides is affected by the molecular
weight. Therefore, separating into fractions with specific range of molecular weight
is important in analyzing and utilizing these bioactivities and physicochemical properties. Fractionation can be carried out using methods such as DEAE-Sepharose Fast
Flow column (Tabarsa et al. 2018).
Co-extraction can be carried out to extract other polymers alongside the ulvan
since the cell walls always contain other useful polysaccharides such as cellulose,
xyloglucans as well as proteins. This would then involve including a separation
process after the extraction stage. The yield and quality of ulvan obtained from
any given biomass depend on the conditions of extraction. Temperature, pH, use
of extractants and concentration of extractant, particle size of biomass, duration of
extraction and pretreatment method are factors which have been identified to affect
the yield and quality of ulvan extraction (Kidgell et al. 2019). The yield is defined
in terms of the quantity of actual extract compared to the known content of ulvan in
the biomass, while the quality is quantified by the degree of polymerization; hence,
molecular weight of the ulvan extracted the purity (i.e., absence of other polymers
and contaminants) and the level of degradation as a result of depolymerization and
desulphurization of the ulvan in the process of extraction.