12 Industrial Extraction of Microalgal Pigments
303
When reacted with calcium hydroxide or acid (such as sulphuric acid, hydrochloric
acid, acetic acid and phosphoric acid), chlorophylls are converted to water-soluble
salts which precipitate out of the organic solvent or pigment mixture and can thus be
removed using a solid-liquid separation technique (such as centrifugation) (Rammuni
et al. 2019). Sulphuric acid (0.01 N) and hydrochloric acid (0.01 N) were able to
successfully precipitate out ~ 80 wt% of the chlorophyll that was co-extracted with
astaxanthin from Monoraphidium sp. GK12 (Fujii 2012).
Phycobiliprotein purification generally involves subjecting the crude pigment
extract to one or more of the following steps: ammonium sulphate precipitation, activated carbon and chitosan precipitation, aqueous two-phase extraction with polyethylene glycol, concentration with ultrafiltration or tangential flow ultrafiltration (3050 kDa), anion exchange chromatography with Q-Sepharose column, gel permeation chromatography with Sephadex G-150 column and anionic chromatography
with diethylaminoethanol cellulose (Benavides and Rito-Palomares 2006; Bermejo
Román et al. 2002; Gantar et al. 2012; Parmar et al. 2011; Sørensen et al. 2013). In
their study purifying PC extracts from Galderis sulphuraria, Sørensen et al. (2013)
found the combination of ammonium sulphate precipitation with aqueous two-phase
extraction and ultrafiltration to result in both the highest PC yield (42 wt% of PC in
the crude extract) and the highest product purity (A620/A280 = 4.5). Gantar et al.
(2012) noted that the increased purities obtained by subjecting pigment extracts to
fractionation steps generally come in expense of their final yields/recoveries. Further
research is needed in order to establish the technical and economic scalability of
pigment purification steps.
12.6 Industrial Scalability
From an industrial perspective, the scalability of a biomass processing pathway is
primarily determined by the intended use of the generated microalgal products. Even
though it is difficult to make this determination without performing a comprehensive
techno-economic analysis of the operational units in each pathway, certain generalisations can be stipulated. Microalgal biomass processing for applications related
to human consumptions (such as pigment recovery for food colorants, nutraceutical
and pharmaceutical products, protein recovery for human diets or food supplements
and cell debris isolation for animal/aquaculture feed) must satisfy the safety and
purity requirements associated with food production. On the other hand, biomass
processing for fuel applications (such as lipid recovery for biodiesel conversion)
must achieve a positive energy balance by minimising the energy requirement of
individual unit operation, in particular that associated with biomass dehydration
during pretreatment and evaporative solvent recovery after the extraction step. For
this reason, the use of less toxic solvents or solvents that are generally accepted as
safe by regulatory food agencies (such as ethanol or acetone) is ideal for pigment
extraction, while the use of volatile solvents with relatively low boiling points and
low enthalpies of vapourisation (such as hexane and ethyl acetate) is preferred for
303
When reacted with calcium hydroxide or acid (such as sulphuric acid, hydrochloric
acid, acetic acid and phosphoric acid), chlorophylls are converted to water-soluble
salts which precipitate out of the organic solvent or pigment mixture and can thus be
removed using a solid-liquid separation technique (such as centrifugation) (Rammuni
et al. 2019). Sulphuric acid (0.01 N) and hydrochloric acid (0.01 N) were able to
successfully precipitate out ~ 80 wt% of the chlorophyll that was co-extracted with
astaxanthin from Monoraphidium sp. GK12 (Fujii 2012).
Phycobiliprotein purification generally involves subjecting the crude pigment
extract to one or more of the following steps: ammonium sulphate precipitation, activated carbon and chitosan precipitation, aqueous two-phase extraction with polyethylene glycol, concentration with ultrafiltration or tangential flow ultrafiltration (3050 kDa), anion exchange chromatography with Q-Sepharose column, gel permeation chromatography with Sephadex G-150 column and anionic chromatography
with diethylaminoethanol cellulose (Benavides and Rito-Palomares 2006; Bermejo
Román et al. 2002; Gantar et al. 2012; Parmar et al. 2011; Sørensen et al. 2013). In
their study purifying PC extracts from Galderis sulphuraria, Sørensen et al. (2013)
found the combination of ammonium sulphate precipitation with aqueous two-phase
extraction and ultrafiltration to result in both the highest PC yield (42 wt% of PC in
the crude extract) and the highest product purity (A620/A280 = 4.5). Gantar et al.
(2012) noted that the increased purities obtained by subjecting pigment extracts to
fractionation steps generally come in expense of their final yields/recoveries. Further
research is needed in order to establish the technical and economic scalability of
pigment purification steps.
12.6 Industrial Scalability
From an industrial perspective, the scalability of a biomass processing pathway is
primarily determined by the intended use of the generated microalgal products. Even
though it is difficult to make this determination without performing a comprehensive
techno-economic analysis of the operational units in each pathway, certain generalisations can be stipulated. Microalgal biomass processing for applications related
to human consumptions (such as pigment recovery for food colorants, nutraceutical
and pharmaceutical products, protein recovery for human diets or food supplements
and cell debris isolation for animal/aquaculture feed) must satisfy the safety and
purity requirements associated with food production. On the other hand, biomass
processing for fuel applications (such as lipid recovery for biodiesel conversion)
must achieve a positive energy balance by minimising the energy requirement of
individual unit operation, in particular that associated with biomass dehydration
during pretreatment and evaporative solvent recovery after the extraction step. For
this reason, the use of less toxic solvents or solvents that are generally accepted as
safe by regulatory food agencies (such as ethanol or acetone) is ideal for pigment
extraction, while the use of volatile solvents with relatively low boiling points and
low enthalpies of vapourisation (such as hexane and ethyl acetate) is preferred for