7.5 Extraction of Agar from Red Seaweed
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beneficial properties in terms of bioactivity such as antioxidant property. An extraction yield of 10–12% is achievable using the hot water method, albeit with brownish
color and impurities (Martinez-Sanz et al. 2019). This method is relatively simpler;
it involves boiling the washed red algae biomass in hot water for an extended period
of time. The liquid extract is then separated from the solid algae residue by filtration.
7.5.4 Enzyme Extraction
Although alkali extraction is more commonly used for extraction of agar, enzymeassisted extraction is also attractive prospect for the potential of low energy requiring and more environmentally friendly extraction process. More recently, enzyme
extraction of agar has been explored. Gel strength of 1521 g/cm
2 , 29.2% 3.6-anhydrol-galactose and 0.84% sulfate content were obtained for agar extracted using the
enzyme-assisted method. The agarase enzyme is capable of breaking the glycosidic
linkages in agar which makes it more readily dissolve in the aqueous medium of
extraction (Xiao et al. 2019). Using the enzyme extraction method to extract agar
from Gracilaria caudata, agar with an average molecular weight of 116.51 kDa and
a degree of sulfation of 0.14% was obtained (Alencar et al. 2019). Although alkali
extraction results in agar with superior properties than enzyme-based extraction of
agar, when considering the environmental impact, the enzyme-based extraction provides a more eco-friendly alternative. The biodegradation of agarose can be used
as a means of extracting agarose oligomers, dimers or monomers from red algae.
Although it results in short-chain degraded agar, these may be useful, for example, the more bioactive oligomeric forms of agar in cosmetics and pharmaceutical
applications.
7.5.5 Ultrasound-Assisted Extraction
Ultrasound is commercially used in the food industry in the extraction and processing of various food compounds in the form of sonication. The ultrasound acts by
creating multiple cavities in the process of formation, expansion and bursting of
these microcavities; they exert pressure on the cell walls causing its disruption. The
combination of the alkali extraction method with sonication results in more effective
extraction process. Although alkali and heat are still required, the time of extraction could be effectively reduced, hence resulting in optimal use of time by up to
fourfold (Martinez-Sanz et al. 2019). It is also possible to reduce the amount of the
alkali required by combining the process with sonication. Unlike in alkali extraction
which results in degradation of some of the agar upon extraction thereby resulting
in reduced yield, use of ultrasound does not alter the yield or properties of the agar
obtained.
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beneficial properties in terms of bioactivity such as antioxidant property. An extraction yield of 10–12% is achievable using the hot water method, albeit with brownish
color and impurities (Martinez-Sanz et al. 2019). This method is relatively simpler;
it involves boiling the washed red algae biomass in hot water for an extended period
of time. The liquid extract is then separated from the solid algae residue by filtration.
7.5.4 Enzyme Extraction
Although alkali extraction is more commonly used for extraction of agar, enzymeassisted extraction is also attractive prospect for the potential of low energy requiring and more environmentally friendly extraction process. More recently, enzyme
extraction of agar has been explored. Gel strength of 1521 g/cm
2 , 29.2% 3.6-anhydrol-galactose and 0.84% sulfate content were obtained for agar extracted using the
enzyme-assisted method. The agarase enzyme is capable of breaking the glycosidic
linkages in agar which makes it more readily dissolve in the aqueous medium of
extraction (Xiao et al. 2019). Using the enzyme extraction method to extract agar
from Gracilaria caudata, agar with an average molecular weight of 116.51 kDa and
a degree of sulfation of 0.14% was obtained (Alencar et al. 2019). Although alkali
extraction results in agar with superior properties than enzyme-based extraction of
agar, when considering the environmental impact, the enzyme-based extraction provides a more eco-friendly alternative. The biodegradation of agarose can be used
as a means of extracting agarose oligomers, dimers or monomers from red algae.
Although it results in short-chain degraded agar, these may be useful, for example, the more bioactive oligomeric forms of agar in cosmetics and pharmaceutical
applications.
7.5.5 Ultrasound-Assisted Extraction
Ultrasound is commercially used in the food industry in the extraction and processing of various food compounds in the form of sonication. The ultrasound acts by
creating multiple cavities in the process of formation, expansion and bursting of
these microcavities; they exert pressure on the cell walls causing its disruption. The
combination of the alkali extraction method with sonication results in more effective
extraction process. Although alkali and heat are still required, the time of extraction could be effectively reduced, hence resulting in optimal use of time by up to
fourfold (Martinez-Sanz et al. 2019). It is also possible to reduce the amount of the
alkali required by combining the process with sonication. Unlike in alkali extraction
which results in degradation of some of the agar upon extraction thereby resulting
in reduced yield, use of ultrasound does not alter the yield or properties of the agar
obtained.