268
R. Halim
(Cuellar-Bermudez et al. 2015; Denery et al. 2004; Molino et al. 2018; Rammuni
et al. 2019).
12.1.1.2 Beta Carotene and D. Salina
β-carotene (C 40 H 56 ) is a yellow-coloured highly unsaturated hydrocarbon (Marchal
et al. 2013; Rammuni et al. 2019). The 9-cis and all-trans stereoisomers are considered
to be the most important because of their physiological roles as pro-vitamin A and
radical quenchers. The 9-cis-β-carotene can only be produced from natural sources
(such as vegetables and microalgae) and has a stronger antioxidant capacity than the
all-trans isomer (Marchal et al. 2013; Rammuni et al. 2019). Even though β-carotene
is present in various microalgal and cyanobacterial species (such as Chlorella zofingiensis, Spirulina platensis and Caulerpa taxifolia), only D.salina has been reported
to be able to accumulate the pigment up to 13 wt% of its cellular biomass (Marchal
et al. 2013; Rammuni et al. 2019). In terms of composition, β-carotene extracted
from D.salina typically consists of ~ 40% all-trans isomer, ~ 40% 9-cis isomer, ~
10% 15-cis isomer and ~ 5% other isomers (Marchal et al. 2013; Rammuni et al.
2019). D. salina cells accumulate β-carotene as droplets in their chloroplast stroma
when exposed to high temperature, high light intensity, high salinity and nitrogen
starvation. D. salina is a highly promising source of β-carotene not only because of
its ability to accumulate 9-cis isomer of the pigment but also because of the fact that
the vegetative form of the cells lacks cell walls and can thus easily be ruptured to
release the intracellular pigments (Marchal et al. 2013; Rammuni et al. 2019).
12.1.2 An Overview of Microalgal Pigment Extraction
Microalgal pigments are intracellular in nature and can generally only be recovered
from the biomass after they have been liberated from the encapsulation of the cell
wall. Microalgal cell walls, however, are composed of tough interlinking biopolymers (Sect. 1.3) that confer the cells with structural strength and formidable defense.
The first step of pigment recovery, therefore, generally consists of a biomass pretreatment step where the cells are subjected to one or more externally applied mechanical,
chemical or enzymatic treatment in order to facilitate disruption, free intracellular
products and improve pigment accessibility to a subsequent extraction step. The
structural strength of microalgal cells is dependent on the thickness, composition
and stratification of their cell walls though these relationships are yet to be fully
understood. Some species have thick and highly rigid cell walls (e.g. Haematococcus pluvialis and Nannochloropsis sp.) which require energy-intensive mechanical treatments (such as high-pressure homogenization and bead milling) or chemical
hydrolyses to rupture, while other species have no cell wall (e.g. Dunaliella salina) or
have less robust cell walls that can be ruptured by simple freeze-thawing or changes
in osmotic pressure (e.g. Rhodomonas salina).
R. Halim
(Cuellar-Bermudez et al. 2015; Denery et al. 2004; Molino et al. 2018; Rammuni
et al. 2019).
12.1.1.2 Beta Carotene and D. Salina
β-carotene (C 40 H 56 ) is a yellow-coloured highly unsaturated hydrocarbon (Marchal
et al. 2013; Rammuni et al. 2019). The 9-cis and all-trans stereoisomers are considered
to be the most important because of their physiological roles as pro-vitamin A and
radical quenchers. The 9-cis-β-carotene can only be produced from natural sources
(such as vegetables and microalgae) and has a stronger antioxidant capacity than the
all-trans isomer (Marchal et al. 2013; Rammuni et al. 2019). Even though β-carotene
is present in various microalgal and cyanobacterial species (such as Chlorella zofingiensis, Spirulina platensis and Caulerpa taxifolia), only D.salina has been reported
to be able to accumulate the pigment up to 13 wt% of its cellular biomass (Marchal
et al. 2013; Rammuni et al. 2019). In terms of composition, β-carotene extracted
from D.salina typically consists of ~ 40% all-trans isomer, ~ 40% 9-cis isomer, ~
10% 15-cis isomer and ~ 5% other isomers (Marchal et al. 2013; Rammuni et al.
2019). D. salina cells accumulate β-carotene as droplets in their chloroplast stroma
when exposed to high temperature, high light intensity, high salinity and nitrogen
starvation. D. salina is a highly promising source of β-carotene not only because of
its ability to accumulate 9-cis isomer of the pigment but also because of the fact that
the vegetative form of the cells lacks cell walls and can thus easily be ruptured to
release the intracellular pigments (Marchal et al. 2013; Rammuni et al. 2019).
12.1.2 An Overview of Microalgal Pigment Extraction
Microalgal pigments are intracellular in nature and can generally only be recovered
from the biomass after they have been liberated from the encapsulation of the cell
wall. Microalgal cell walls, however, are composed of tough interlinking biopolymers (Sect. 1.3) that confer the cells with structural strength and formidable defense.
The first step of pigment recovery, therefore, generally consists of a biomass pretreatment step where the cells are subjected to one or more externally applied mechanical,
chemical or enzymatic treatment in order to facilitate disruption, free intracellular
products and improve pigment accessibility to a subsequent extraction step. The
structural strength of microalgal cells is dependent on the thickness, composition
and stratification of their cell walls though these relationships are yet to be fully
understood. Some species have thick and highly rigid cell walls (e.g. Haematococcus pluvialis and Nannochloropsis sp.) which require energy-intensive mechanical treatments (such as high-pressure homogenization and bead milling) or chemical
hydrolyses to rupture, while other species have no cell wall (e.g. Dunaliella salina) or
have less robust cell walls that can be ruptured by simple freeze-thawing or changes
in osmotic pressure (e.g. Rhodomonas salina).