6.4 Availability of Raw Materials
129
According to FAO reports, production of some red algae species has increased
in the past 10 years while some have dropped. K. alvarezii, for example, showed
annual increase in production from 1285 MT in 2005 to 1963 in 2012. This was
then followed by a decline to 1726 MT in 2013 to 1527 in 2016 (FAO 2018). On the
other hand, Porphyra has shown a general annual rise from 703,000 tonnes in 2005 to
1,353,000 tonnes in 2016. This excludes a drop from 1,072,000 to 1,123,000 tonnes
between 2010 and 2012. On this basis, the future availability of red algae is quite
unpredictable.
The factors which may pose a threat to the availability of red algae are interwoven with the factors which pose a threat to the aquatic environment as a whole.
Exploring renewable sources of polymers used in products such as processing agents,
packaging, energy storage, printing, cosmetics and textiles is a route to abating the
threat of depleting fossil fuel reserves. The other issue is the impact of the process
of extraction of these resources on the environment. The next section explores the
environmental impact of producing carrageenan from red algae.
6.5 Extraction of Carrageenan
Carrageenan is soluble in aqueous alkali solution at high temperature and insoluble
in alcohol and certain salt solutions (Williams and Phillips 2003), and this property
serves as a basis for its extraction from red seaweed. Alkalis commonly used include
sodium hydroxide, potassium hydroxide and calcium hydroxide. Here, we use a
typical chemical extraction process as used in the literature (Manuhara et al. 2016)
and an enzyme extraction method used by Souza et al (2018). Variations in method
include change in the choice of alkali, use of enzymes and extraction conditions such
as extraction pH, temperature and time.
6.5.1 Chemical Extraction
In the chemical extraction method by Manuhara et al. (2016), the collected red algae
biomass is washed with water and then soaked in water for 24 h to soften. The wet
biomass is then pulverized until a pulp is obtained. Extraction is carried out in alkali
solution of calcium hydroxide at a pH of 9. The system is heated to 90 °C and the
extraction carried out for 2 h under continuous stirring. The alkali serves to decrease
the degree of sulfation and also increase the number of 3,6 anhydrous carrageenan
units. This makes for stronger gels (McHugh 2003). The mass is then separated by
filtration. The liquid filtrate which contains the carrageenan is retained for further
purification. Hydrochloric acid is added until the pH reduces to 7. The neutralized
liquid filtrate is then heated at 60 °C for 30 min. At this point, the filtrate contains
other soluble molecules; therefore, the carrageenan needs to be precipitated out of
the solution. This is done using potassium chloride (KCl) at a concentration which
129
According to FAO reports, production of some red algae species has increased
in the past 10 years while some have dropped. K. alvarezii, for example, showed
annual increase in production from 1285 MT in 2005 to 1963 in 2012. This was
then followed by a decline to 1726 MT in 2013 to 1527 in 2016 (FAO 2018). On the
other hand, Porphyra has shown a general annual rise from 703,000 tonnes in 2005 to
1,353,000 tonnes in 2016. This excludes a drop from 1,072,000 to 1,123,000 tonnes
between 2010 and 2012. On this basis, the future availability of red algae is quite
unpredictable.
The factors which may pose a threat to the availability of red algae are interwoven with the factors which pose a threat to the aquatic environment as a whole.
Exploring renewable sources of polymers used in products such as processing agents,
packaging, energy storage, printing, cosmetics and textiles is a route to abating the
threat of depleting fossil fuel reserves. The other issue is the impact of the process
of extraction of these resources on the environment. The next section explores the
environmental impact of producing carrageenan from red algae.
6.5 Extraction of Carrageenan
Carrageenan is soluble in aqueous alkali solution at high temperature and insoluble
in alcohol and certain salt solutions (Williams and Phillips 2003), and this property
serves as a basis for its extraction from red seaweed. Alkalis commonly used include
sodium hydroxide, potassium hydroxide and calcium hydroxide. Here, we use a
typical chemical extraction process as used in the literature (Manuhara et al. 2016)
and an enzyme extraction method used by Souza et al (2018). Variations in method
include change in the choice of alkali, use of enzymes and extraction conditions such
as extraction pH, temperature and time.
6.5.1 Chemical Extraction
In the chemical extraction method by Manuhara et al. (2016), the collected red algae
biomass is washed with water and then soaked in water for 24 h to soften. The wet
biomass is then pulverized until a pulp is obtained. Extraction is carried out in alkali
solution of calcium hydroxide at a pH of 9. The system is heated to 90 °C and the
extraction carried out for 2 h under continuous stirring. The alkali serves to decrease
the degree of sulfation and also increase the number of 3,6 anhydrous carrageenan
units. This makes for stronger gels (McHugh 2003). The mass is then separated by
filtration. The liquid filtrate which contains the carrageenan is retained for further
purification. Hydrochloric acid is added until the pH reduces to 7. The neutralized
liquid filtrate is then heated at 60 °C for 30 min. At this point, the filtrate contains
other soluble molecules; therefore, the carrageenan needs to be precipitated out of
the solution. This is done using potassium chloride (KCl) at a concentration which