13 Process Intensification Aspects of Extraction …
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main application in the cell disruption stage where passage of electrical current results
in enhanced extraction of desired pigment (Golberg et al. 2016). Very few studies
are reported for the MEF and HVED assisted extraction processes while PEF has
found wide range applications and hence has been discussed in detail here.
PEF is a non-thermal process consisting of treatment of the material with unipolar
or bipolar pulses applied in square wave or exponential shaped frequencies. Biomaterial is typically subjected to repetitive electric frequencies with intense electric field
ranging from 0.1–80 kV/cm for a very short time period ranging in nano to milliseconds (Mahesha et al. 2017). PEF causes reversible or irreversible pore formation
in cell membrane causing rapid solvent diffusion with enhanced mass transfer of
intracellular components in the subsequent extraction stage. It is important to note
that selective extraction of components can be achieved with controlled pore formation depending on electric intensity and cell characteristics (Raso et al. 2016). We
now present some case studies to understand the efficacy of PEF.
C. vulgaris when subjected to PEF at 20–25 kV/cm field strength for a period
of 3 μs pulse duration was reported to give irreversible pore formation yielding a
higher pigment yield of 0.82 mg/g after pretreatment. A subsequent 1 h incubation
was also reported to enhance the pigment yield to 1.04 mg/g (Luengo et al. 2014).
Incubation of microalgae after pretreatment results in plasmolysis of the chloroplast
due to osmolytic disequilibrium, which assists the process of pigment extraction.
The time of PEF treatment also affects the final yield of the product. In a study
performed by Luengo et al. (2015a, b), higher yield of 1.58 mg/L was reported
by using microsecond (μs) range of treatment as compared to 1.09 mg/L of yield
obtained at millisecond (ms) range of treatment. Similar to effect of time, operating
pH also plays a major role in deciding enhancement in yields due to the PEF. Parniakov et al. (2015b) studied the carotenoid pigment extraction from Nannochloropsis
sp. and reported that using PEF at pH of 8.5 resulted in enhanced yield of 0.2 mg/g
as compared to 0.04 mg/g yield obtained using normal distilled water. Combination of PEF with biphasic mixtures of organic solvents has also been reported in
few studies as an approach for intensifying the recovery of pigments. Parniakov
et al. (2015c) combined PEF with biphasic mixture of dimethyl sulfoxide/ethanol
and water reporting increased yield of pigment extraction as compared to conventional process of only biphasic mixture-based extraction or PEF alone (Parniakov
et al. 2015c). In another reported study, Heterochlorella luteoviridis was subjected
to MEF at 180 V and 60 Hz for 50 min combined with ethanol as solvent where
higher lutein yield of 1.21 mg/g was obtained (Jaeschke et al. 2016). Application
of moderate thermal treatment along-with PEF has also been reported to increase
pigment extraction yield. Lutein extraction from C. vulgaris with PEF along-with
thermal treatment at 40 °C was reported to result in 4.5 fold increase in the production
(Luengo et al. 2015a). Increase in yield using PEF along-with higher temperature is
attributed to the increased membrane permeability. Though PEF has been reported
to be successful for variety of lab scale applications, its application at commercial
scale will be limited mainly to specific high-value pigment extraction processes due
to the associated higher costs of operation.
317
main application in the cell disruption stage where passage of electrical current results
in enhanced extraction of desired pigment (Golberg et al. 2016). Very few studies
are reported for the MEF and HVED assisted extraction processes while PEF has
found wide range applications and hence has been discussed in detail here.
PEF is a non-thermal process consisting of treatment of the material with unipolar
or bipolar pulses applied in square wave or exponential shaped frequencies. Biomaterial is typically subjected to repetitive electric frequencies with intense electric field
ranging from 0.1–80 kV/cm for a very short time period ranging in nano to milliseconds (Mahesha et al. 2017). PEF causes reversible or irreversible pore formation
in cell membrane causing rapid solvent diffusion with enhanced mass transfer of
intracellular components in the subsequent extraction stage. It is important to note
that selective extraction of components can be achieved with controlled pore formation depending on electric intensity and cell characteristics (Raso et al. 2016). We
now present some case studies to understand the efficacy of PEF.
C. vulgaris when subjected to PEF at 20–25 kV/cm field strength for a period
of 3 μs pulse duration was reported to give irreversible pore formation yielding a
higher pigment yield of 0.82 mg/g after pretreatment. A subsequent 1 h incubation
was also reported to enhance the pigment yield to 1.04 mg/g (Luengo et al. 2014).
Incubation of microalgae after pretreatment results in plasmolysis of the chloroplast
due to osmolytic disequilibrium, which assists the process of pigment extraction.
The time of PEF treatment also affects the final yield of the product. In a study
performed by Luengo et al. (2015a, b), higher yield of 1.58 mg/L was reported
by using microsecond (μs) range of treatment as compared to 1.09 mg/L of yield
obtained at millisecond (ms) range of treatment. Similar to effect of time, operating
pH also plays a major role in deciding enhancement in yields due to the PEF. Parniakov et al. (2015b) studied the carotenoid pigment extraction from Nannochloropsis
sp. and reported that using PEF at pH of 8.5 resulted in enhanced yield of 0.2 mg/g
as compared to 0.04 mg/g yield obtained using normal distilled water. Combination of PEF with biphasic mixtures of organic solvents has also been reported in
few studies as an approach for intensifying the recovery of pigments. Parniakov
et al. (2015c) combined PEF with biphasic mixture of dimethyl sulfoxide/ethanol
and water reporting increased yield of pigment extraction as compared to conventional process of only biphasic mixture-based extraction or PEF alone (Parniakov
et al. 2015c). In another reported study, Heterochlorella luteoviridis was subjected
to MEF at 180 V and 60 Hz for 50 min combined with ethanol as solvent where
higher lutein yield of 1.21 mg/g was obtained (Jaeschke et al. 2016). Application
of moderate thermal treatment along-with PEF has also been reported to increase
pigment extraction yield. Lutein extraction from C. vulgaris with PEF along-with
thermal treatment at 40 °C was reported to result in 4.5 fold increase in the production
(Luengo et al. 2015a). Increase in yield using PEF along-with higher temperature is
attributed to the increased membrane permeability. Though PEF has been reported
to be successful for variety of lab scale applications, its application at commercial
scale will be limited mainly to specific high-value pigment extraction processes due
to the associated higher costs of operation.