Microalgal Downstream Processing: Harvesting, Drying, Extraction, Separation, and Purification 103
In another study bead beating of lyophilized P. tricornutum allowed the recovery of total lipids in
similar amount as when performing disruption with sonication (Ryckebosch et al. 2012). In a comparative
study of various disruptive techniques (high pressure homogenization, acid, ultrasonic, and bead beating
treatments), Halim et al. (2012) found out that bead beating had a moderate efficiency with an average
disruption of 17.5% of the initial intact cells of the microalga Chlorococcum sp. stock culture as evaluated
by microscopic observation. The efficiency of bead beating was improved by a factor 1.5 when bead
loading was increased from 1:2 to 1:3 (volumetric ratio of glass beads to microalgal stock culture).
Apart from bead millers, mechanical shear can be achieved by using a simple blender. N. oculata
cells subjected to a treatment with a hand blender (3,000 rpm for 6 min) led to a 92.95% cell disruption
quantified by direct optical microscopy techniques (McMillan et al. 2013).
Pulsed electric field
With this technique, the cell membrane is disrupted by unequal electric charges that accumulate on
dipolar molecules, thus creating a pressure on the membrane leading to the formation of irreversible
pores in the membrane.
Sheng et al. (2012) investigated this technique for the extraction of lipids from Synechocystis PCC
6803. This work showed that pulsed electric field (36 kWh/m
3
) and a final temperature of 36ºC afforded
high yield of suspended lipids (4.4% of total biomass). The authors of this work concluded that pulsed
electric field, together with microwave treatment, was the best suited technique for large scale cell
disruption because it retained most of the lipids in the suspended phase, thus reducing the use of solvent
for downstream extraction.
Microwave
The mechanism by which microwave treatment disrupts the membranes depends on the rotation of
molecular dipoles thus disrupting weak hydrogen bonds and resulting in dielectric heating. This increases
the solvent penetration into the matrix and facilitates analyte solvation.
Sheng et al. (2012) showed that by using microwaves without temperature control (1.4 kW for a
treatment of 1 min and a final temperature of 57ºC), lipid extraction as suspend FAME was maximized
(4.6% of total biomass) from Synechocystis PCC 6803.
N. oculata cells subjected to a microwave treatment with temperature control (90ºC, power varying
from 210 to 1,025 W) led to a 94.92% cell disruption quantified by direct optical microscopy techniques
(McMillan et al. 2013). The efficiency of the microwave treatment could be seen during lipid extraction
from N. oculata as the lipid recovery was improved from 1.4 to a maximum of 11.3% (weight %) at
120ºC (Biller et al. 2013). For this same alga, Koberg et al. (2011) also report that microwave is very
efficient for lipid extraction as they obtained a biodiesel yield of 32.8%, a figure which was a factor 1.74
higher than when the extraction was carried out with sonication.
Laser treatment
Algal cells of N. oculata subjected to a laser treatment (Nd:YV04 laser with a transition wavelength of
1,064 nm, 10 W, and 20 kHz) for 60 s at 80% power level led to a 96.53% cell disruption quantified by
direct optical microscopy techniques (McMillan et al. 2013) and this treatment was the most efficient to
disrupt this algal cell wall when compared to microwave, water bath, blender, and ultrasonic treatments.
Chemical disruption treatments
Enzymatic pretreatment
Microalgae cell walls can be disrupted using an enzymatic approach. Enzymes have to be selected
according to the algal species to be treated due to the specificity of their membranes and cell walls.
Such a screening was carried out by Horst et al. (2012). Several enzymes with known properties were
In another study bead beating of lyophilized P. tricornutum allowed the recovery of total lipids in
similar amount as when performing disruption with sonication (Ryckebosch et al. 2012). In a comparative
study of various disruptive techniques (high pressure homogenization, acid, ultrasonic, and bead beating
treatments), Halim et al. (2012) found out that bead beating had a moderate efficiency with an average
disruption of 17.5% of the initial intact cells of the microalga Chlorococcum sp. stock culture as evaluated
by microscopic observation. The efficiency of bead beating was improved by a factor 1.5 when bead
loading was increased from 1:2 to 1:3 (volumetric ratio of glass beads to microalgal stock culture).
Apart from bead millers, mechanical shear can be achieved by using a simple blender. N. oculata
cells subjected to a treatment with a hand blender (3,000 rpm for 6 min) led to a 92.95% cell disruption
quantified by direct optical microscopy techniques (McMillan et al. 2013).
Pulsed electric field
With this technique, the cell membrane is disrupted by unequal electric charges that accumulate on
dipolar molecules, thus creating a pressure on the membrane leading to the formation of irreversible
pores in the membrane.
Sheng et al. (2012) investigated this technique for the extraction of lipids from Synechocystis PCC
6803. This work showed that pulsed electric field (36 kWh/m
3
) and a final temperature of 36ºC afforded
high yield of suspended lipids (4.4% of total biomass). The authors of this work concluded that pulsed
electric field, together with microwave treatment, was the best suited technique for large scale cell
disruption because it retained most of the lipids in the suspended phase, thus reducing the use of solvent
for downstream extraction.
Microwave
The mechanism by which microwave treatment disrupts the membranes depends on the rotation of
molecular dipoles thus disrupting weak hydrogen bonds and resulting in dielectric heating. This increases
the solvent penetration into the matrix and facilitates analyte solvation.
Sheng et al. (2012) showed that by using microwaves without temperature control (1.4 kW for a
treatment of 1 min and a final temperature of 57ºC), lipid extraction as suspend FAME was maximized
(4.6% of total biomass) from Synechocystis PCC 6803.
N. oculata cells subjected to a microwave treatment with temperature control (90ºC, power varying
from 210 to 1,025 W) led to a 94.92% cell disruption quantified by direct optical microscopy techniques
(McMillan et al. 2013). The efficiency of the microwave treatment could be seen during lipid extraction
from N. oculata as the lipid recovery was improved from 1.4 to a maximum of 11.3% (weight %) at
120ºC (Biller et al. 2013). For this same alga, Koberg et al. (2011) also report that microwave is very
efficient for lipid extraction as they obtained a biodiesel yield of 32.8%, a figure which was a factor 1.74
higher than when the extraction was carried out with sonication.
Laser treatment
Algal cells of N. oculata subjected to a laser treatment (Nd:YV04 laser with a transition wavelength of
1,064 nm, 10 W, and 20 kHz) for 60 s at 80% power level led to a 96.53% cell disruption quantified by
direct optical microscopy techniques (McMillan et al. 2013) and this treatment was the most efficient to
disrupt this algal cell wall when compared to microwave, water bath, blender, and ultrasonic treatments.
Chemical disruption treatments
Enzymatic pretreatment
Microalgae cell walls can be disrupted using an enzymatic approach. Enzymes have to be selected
according to the algal species to be treated due to the specificity of their membranes and cell walls.
Such a screening was carried out by Horst et al. (2012). Several enzymes with known properties were