12 Industrial Extraction of Microalgal Pigments
269
Once the cells are ruptured, they are then subjected to an extraction step in order
to recover the released intracellular pigments. The extraction solvent used for the
recovery step will depend on the solubility of the targeted pigment(s). Chlorophylls
and carotenoids are not soluble in water and therefore require the addition of organic
solvents (such as acetone, ethanol, methanol, ethyl acetate) or supercritical carbon
dioxide for their recoveries. The extraction step is often pressurised or coupled
with an ancillary rupture process (such as microwave or ultrasonication) in order
to enhance mass transfer and thus pigment recovery. Phycobiliproteins, on the other
hand, are soluble in water and do not require the use of organic solvents or supercritical carbon dioxide for their extraction. Aqueous buffer with a stable pH (such as
phosphate buffer) is often used instead of water in order to prevent potential pigment
degradation.
Table 12.1 provides a summary of the different biomass pretreatments and extraction solvents that have been used in previous research to recover pigments from
microalgal biomass. Despite our best efforts to ensure its completeness, we note
that the list is by no means comprehensive and some technological options might
have been overlooked. Cyanobacteria (such as Spirulina platensis) and their pigment
recoveries have been included in Table 12.1 and various discussions throughout
this review for their high phycobiliprotein contents and processing similarities to
microalgal biomass. Even though the chapter reviews a wide spectrum of principles and technologies associated with biomass pretreatment and pigment recovery, it
focuses its discussion on the recoveries of four industrially valuable pigments from
their algal biomass sources (e.g. astaxanthin from H. pluvialis, β-carotene from D.
salina, phycoerythrin from Porphyridium cruentum and phycocyanin from Spirulina
platensis).
Section 12.2 of the chapter evaluates the range of technological options that
can be used to rupture microalgal cell walls and release intracellular pigments,
while Sect. 12.3 examines the different extraction technologies that are currently
available for extracting the released pigments from ruptured biomass. Section 12.4
reviews different biomass processing pathways that have been recently studied for
the recoveries of industrially valuable pigments from algal sources (astaxanthin,
β-carotene, phycoerythrin, phycocyanin) and summarises key findings from these
studies. Section 12.5 outlines the array of technological options available for the
purification of pigments after they have been extracted from the microalgal biomass.
Finally, Sect. 12.6 evaluates the industrial scalability of pigment extraction in the
wider context of a microalgal biorefinery system and provides a recommendation on
the future research direction of microalgal pigment extraction.
12.1.3 Microalgal Cell Wall: Structure and Composition
Microalgal cell walls are complex, extremely diverse and poorly understood. The
ultrastructure and biochemical composition of a microalgal cell wall are generally
determined by the strain’s phylogenetic classification, with different species grouped
269
Once the cells are ruptured, they are then subjected to an extraction step in order
to recover the released intracellular pigments. The extraction solvent used for the
recovery step will depend on the solubility of the targeted pigment(s). Chlorophylls
and carotenoids are not soluble in water and therefore require the addition of organic
solvents (such as acetone, ethanol, methanol, ethyl acetate) or supercritical carbon
dioxide for their recoveries. The extraction step is often pressurised or coupled
with an ancillary rupture process (such as microwave or ultrasonication) in order
to enhance mass transfer and thus pigment recovery. Phycobiliproteins, on the other
hand, are soluble in water and do not require the use of organic solvents or supercritical carbon dioxide for their extraction. Aqueous buffer with a stable pH (such as
phosphate buffer) is often used instead of water in order to prevent potential pigment
degradation.
Table 12.1 provides a summary of the different biomass pretreatments and extraction solvents that have been used in previous research to recover pigments from
microalgal biomass. Despite our best efforts to ensure its completeness, we note
that the list is by no means comprehensive and some technological options might
have been overlooked. Cyanobacteria (such as Spirulina platensis) and their pigment
recoveries have been included in Table 12.1 and various discussions throughout
this review for their high phycobiliprotein contents and processing similarities to
microalgal biomass. Even though the chapter reviews a wide spectrum of principles and technologies associated with biomass pretreatment and pigment recovery, it
focuses its discussion on the recoveries of four industrially valuable pigments from
their algal biomass sources (e.g. astaxanthin from H. pluvialis, β-carotene from D.
salina, phycoerythrin from Porphyridium cruentum and phycocyanin from Spirulina
platensis).
Section 12.2 of the chapter evaluates the range of technological options that
can be used to rupture microalgal cell walls and release intracellular pigments,
while Sect. 12.3 examines the different extraction technologies that are currently
available for extracting the released pigments from ruptured biomass. Section 12.4
reviews different biomass processing pathways that have been recently studied for
the recoveries of industrially valuable pigments from algal sources (astaxanthin,
β-carotene, phycoerythrin, phycocyanin) and summarises key findings from these
studies. Section 12.5 outlines the array of technological options available for the
purification of pigments after they have been extracted from the microalgal biomass.
Finally, Sect. 12.6 evaluates the industrial scalability of pigment extraction in the
wider context of a microalgal biorefinery system and provides a recommendation on
the future research direction of microalgal pigment extraction.
12.1.3 Microalgal Cell Wall: Structure and Composition
Microalgal cell walls are complex, extremely diverse and poorly understood. The
ultrastructure and biochemical composition of a microalgal cell wall are generally
determined by the strain’s phylogenetic classification, with different species grouped