12 Industrial Extraction of Microalgal Pigments
277
medium with lower salt concentration or fresh water (Dong et al. 2016). The effectiveness of osmotic shock appears to be highly species dependent and, as such, the
treatment may not be the most reliable method for cell rupture.
12.2.6 Microwaves
The transmission of microwave energy into cell suspension triggers rapid vibration
of the liquid particles and leads to rapid heating of the cell matrix. The increase in
intracellular kinetic energy exerts pressure on the cell wall and leads to cell rupture
(Balasubramanian et al. 2011; Dong et al. 2016; Rammuni et al. 2019). A number
of previous studies (Balasubramanian et al. 2011; Lee et al. 2010; Zhao et al. 2009)
have applied microwave treatment on different microalgal species and demonstrated
its ability to increase the yield of both lipid and pigment extractions (total lipid
from Scenedesmus obliquus, Botryococcus sp., C. vulgaris, and Scenedesmus sp.,
astaxanthin from H.pluvialis) (Table 12.3). Similar to HPH, the use of microwave
treatment can potentially lead to severe emulsion formation that impedes solvent
recovery.
12.2.7 Enzymatic Treatment
Various studies have used enzymatic treatments as means to hydrolyse algal cell walls
for carbohydrate solubilisation, lipid extraction and pigment extraction (Demuez
et al. 2015; Dong et al. 2016; Gerken et al. 2013; Grossman et al. 2011; Kobayashi
et al. 1997; Zuorro et al. 2016). The hydrolysis step normally requires a cocktail of
different enzymes, the formulation of which will depend on the composition of the
cell wall to be hydrolysed. Since cell wall configuration varies considerably between
species, the composition of the enzyme cocktail needs to be tailored and optimised
for each specific biomass. Enzymes are expensive and need to be recovered and
reused for the treatment to be economically scalable. Because enzymatic hydrolysis
is normally carried out at a relatively low temperature, it has the potential to be used
in the recovery of thermally sensitive/labile products (Demuez et al. 2015; Dong et al.
2016; Gerken et al. 2013; Grossman et al. 2011; Kobayashi et al. 1997; Zuorro et al.
2016). Chlorella has previously been shown to be vulnerable to enzymes that attack
sugar polymers containing N-acetylglucosamine, such as chitinases and lysozymes.
Nannochloropsis, on the other hand, was found to be susceptible to enzymes that
degrade glucose polymers, such as cellulose and hemicellulose (Demuez et al. 2015;
Dong et al. 2016; Gerken et al. 2013; Grossman et al. 2011; Kobayashi et al. 1997;
Zuorro et al. 2016). Kobayahi et al. (1997) found the extractability of astaxanthin from
H. pluvialis to be significantly enhanced after the biomass was treated with one of the
following enzymes: β-1,3-glucanase, cellulase, β-1,4-glucanase or β-glucuronidase.
277
medium with lower salt concentration or fresh water (Dong et al. 2016). The effectiveness of osmotic shock appears to be highly species dependent and, as such, the
treatment may not be the most reliable method for cell rupture.
12.2.6 Microwaves
The transmission of microwave energy into cell suspension triggers rapid vibration
of the liquid particles and leads to rapid heating of the cell matrix. The increase in
intracellular kinetic energy exerts pressure on the cell wall and leads to cell rupture
(Balasubramanian et al. 2011; Dong et al. 2016; Rammuni et al. 2019). A number
of previous studies (Balasubramanian et al. 2011; Lee et al. 2010; Zhao et al. 2009)
have applied microwave treatment on different microalgal species and demonstrated
its ability to increase the yield of both lipid and pigment extractions (total lipid
from Scenedesmus obliquus, Botryococcus sp., C. vulgaris, and Scenedesmus sp.,
astaxanthin from H.pluvialis) (Table 12.3). Similar to HPH, the use of microwave
treatment can potentially lead to severe emulsion formation that impedes solvent
recovery.
12.2.7 Enzymatic Treatment
Various studies have used enzymatic treatments as means to hydrolyse algal cell walls
for carbohydrate solubilisation, lipid extraction and pigment extraction (Demuez
et al. 2015; Dong et al. 2016; Gerken et al. 2013; Grossman et al. 2011; Kobayashi
et al. 1997; Zuorro et al. 2016). The hydrolysis step normally requires a cocktail of
different enzymes, the formulation of which will depend on the composition of the
cell wall to be hydrolysed. Since cell wall configuration varies considerably between
species, the composition of the enzyme cocktail needs to be tailored and optimised
for each specific biomass. Enzymes are expensive and need to be recovered and
reused for the treatment to be economically scalable. Because enzymatic hydrolysis
is normally carried out at a relatively low temperature, it has the potential to be used
in the recovery of thermally sensitive/labile products (Demuez et al. 2015; Dong et al.
2016; Gerken et al. 2013; Grossman et al. 2011; Kobayashi et al. 1997; Zuorro et al.
2016). Chlorella has previously been shown to be vulnerable to enzymes that attack
sugar polymers containing N-acetylglucosamine, such as chitinases and lysozymes.
Nannochloropsis, on the other hand, was found to be susceptible to enzymes that
degrade glucose polymers, such as cellulose and hemicellulose (Demuez et al. 2015;
Dong et al. 2016; Gerken et al. 2013; Grossman et al. 2011; Kobayashi et al. 1997;
Zuorro et al. 2016). Kobayahi et al. (1997) found the extractability of astaxanthin from
H. pluvialis to be significantly enhanced after the biomass was treated with one of the
following enzymes: β-1,3-glucanase, cellulase, β-1,4-glucanase or β-glucuronidase.