Microalgal Downstream Processing: Harvesting, Drying, Extraction, Separation, and Purification 109
Zeaxanthin was extracted from N. oculata by acetone using an ultrasonic extractor (Chen et al.
2012a). The extract obtained was then chromatographed on a reverse phase polystyrene-based resin,
PS100. Elution was carried out isocratically with the mobile phase methanol:acetone (90:10 v/v) at
a flow rate of 65 mL/min. This chromatography step increased the concentration of zeaxanthin from
36.2 mg/g of the ultrasonic extract to 425.6 mg/g of the collected column fraction.
Phycobilliproteins obtained by precipitation usually require further purification. Básaca-Loya
et al. (2009) for instance first chromatographed the protein fraction on Sephadex G-25 to remove the
ammonium sulfate, then on an anionic HiPrep 16/10 Q XL chromatographic column and finally on a
Zorbax GF-250 HPLC column to get purified β-phycoerythrin.
Soluble proteins from the alga Tetraselmis sp. were isolated under mild, non-denaturing conditions
(Schwenzfeier et al. 2011). Chromatography was one of the purification steps of this process. The
stationary phase was an EBA ion exchange adsorbent Streamline DEAE and after application of the alga
extract the bound proteins were eluted using a 35 mM potassium phosphate buffer containing 2M NaCl.
Crystallization
A zeaxanthin extract of N. oculata was further purified by using supercritical anti-solvent recrystallization
(Chen et al. 2012a) after a response surface methodology was systematically applied to optimize the
process. Zeaxanthin-rich particles with a purity of 84.2% and a recovery of 85.3% were obtained from
the recrystallization process using the optimized feed concentration of 1.5 mg/mL, CO 2 flow rate of 48.6
g/min and a pressure of 135 bar.
Conclusion
On the one hand, most work carried out on culture of microalgae to date mainly focuses on the extraction
of lipids from the algal biomass for the production of biodiesel, as microalgae could be a good alternative
to terrestrial crops. Chisti (2008) estimated that microalgae biodiesel production would only need 3%
of the United States cultivable land to replace all of US petroleum based transport fuels. However, the
cost of production of microalgae biodiesel is still not competitive with fossil fuels and consequently,
the commercialization of microalgae biodiesel is still far from reality. On the other hand, some high
value compounds, such as carotenoids, have been extracted and commercialized from microalgae. Due
to their market prices, these compounds justify the use of separation and extraction processes which are
more energy demanding. However, the current harvesting, dewatering, and cell disrupting techniques are
still too energy and time consuming, and are therefore a bottleneck hindering economic industrial-scale
production of microalgae. Most of these techniques have to be optimized for each specific alga and for the
compounds to be extracted from the algal biomass, and this contributes to the overall production costs.
Further research is clearly needed to streamline these novel technologies to an industrial scale so that the
algal components can be exploited by the industry.
References
Adam, F., M. Abert-Vian, G. Peltier and F. Chemat. 2012. “Solvent-free” ultrasound-assisted extraction of lipids from fresh
microalgae cells: a green, clean and scalable process. Bioresour. Technol. 114: 457–465.
Ahmad, A.L., N.H. Mat Yasin, C.J.C. Derek and J.K. Lim. 2011. Optimization of microalgae coagulation process using
chitosan. Chem. Eng. J. 173: 879–882.
Amirtharajah, A. and K.M. Mills. 1982. Rapid-mix design for mechanism of alum coagulation. J. Am. Water Works Ass. 74:
210–216.
Bajaj, I.B. and R.S. Singhal. 2011. Flocculation properties of poly(γ-glutamic acid) produced from Bacillus subtilis isolate.
Food Bioprocess. Technol. 4: 745–752.
Balasubramanian, R.K., T.T.Y. Doan and J.P. Obbard. 2013. Factors affecting cellular lipid extraction from marine microalgae.
Chem. Eng. J. 215-216: 929–936.
Básaca-Loya, G.A., M.A. Valdez, E.A. Enríquez-Guevara, L.E. Gutiérrez-Millán and M.G. Burboa. 2009. Extraction and
purification of B-phycoerythrin from the red microalga Rhodosorus marinus. Cienc. Mar. 35: 359–368.
Zeaxanthin was extracted from N. oculata by acetone using an ultrasonic extractor (Chen et al.
2012a). The extract obtained was then chromatographed on a reverse phase polystyrene-based resin,
PS100. Elution was carried out isocratically with the mobile phase methanol:acetone (90:10 v/v) at
a flow rate of 65 mL/min. This chromatography step increased the concentration of zeaxanthin from
36.2 mg/g of the ultrasonic extract to 425.6 mg/g of the collected column fraction.
Phycobilliproteins obtained by precipitation usually require further purification. Básaca-Loya
et al. (2009) for instance first chromatographed the protein fraction on Sephadex G-25 to remove the
ammonium sulfate, then on an anionic HiPrep 16/10 Q XL chromatographic column and finally on a
Zorbax GF-250 HPLC column to get purified β-phycoerythrin.
Soluble proteins from the alga Tetraselmis sp. were isolated under mild, non-denaturing conditions
(Schwenzfeier et al. 2011). Chromatography was one of the purification steps of this process. The
stationary phase was an EBA ion exchange adsorbent Streamline DEAE and after application of the alga
extract the bound proteins were eluted using a 35 mM potassium phosphate buffer containing 2M NaCl.
Crystallization
A zeaxanthin extract of N. oculata was further purified by using supercritical anti-solvent recrystallization
(Chen et al. 2012a) after a response surface methodology was systematically applied to optimize the
process. Zeaxanthin-rich particles with a purity of 84.2% and a recovery of 85.3% were obtained from
the recrystallization process using the optimized feed concentration of 1.5 mg/mL, CO 2 flow rate of 48.6
g/min and a pressure of 135 bar.
Conclusion
On the one hand, most work carried out on culture of microalgae to date mainly focuses on the extraction
of lipids from the algal biomass for the production of biodiesel, as microalgae could be a good alternative
to terrestrial crops. Chisti (2008) estimated that microalgae biodiesel production would only need 3%
of the United States cultivable land to replace all of US petroleum based transport fuels. However, the
cost of production of microalgae biodiesel is still not competitive with fossil fuels and consequently,
the commercialization of microalgae biodiesel is still far from reality. On the other hand, some high
value compounds, such as carotenoids, have been extracted and commercialized from microalgae. Due
to their market prices, these compounds justify the use of separation and extraction processes which are
more energy demanding. However, the current harvesting, dewatering, and cell disrupting techniques are
still too energy and time consuming, and are therefore a bottleneck hindering economic industrial-scale
production of microalgae. Most of these techniques have to be optimized for each specific alga and for the
compounds to be extracted from the algal biomass, and this contributes to the overall production costs.
Further research is clearly needed to streamline these novel technologies to an industrial scale so that the
algal components can be exploited by the industry.
References
Adam, F., M. Abert-Vian, G. Peltier and F. Chemat. 2012. “Solvent-free” ultrasound-assisted extraction of lipids from fresh
microalgae cells: a green, clean and scalable process. Bioresour. Technol. 114: 457–465.
Ahmad, A.L., N.H. Mat Yasin, C.J.C. Derek and J.K. Lim. 2011. Optimization of microalgae coagulation process using
chitosan. Chem. Eng. J. 173: 879–882.
Amirtharajah, A. and K.M. Mills. 1982. Rapid-mix design for mechanism of alum coagulation. J. Am. Water Works Ass. 74:
210–216.
Bajaj, I.B. and R.S. Singhal. 2011. Flocculation properties of poly(γ-glutamic acid) produced from Bacillus subtilis isolate.
Food Bioprocess. Technol. 4: 745–752.
Balasubramanian, R.K., T.T.Y. Doan and J.P. Obbard. 2013. Factors affecting cellular lipid extraction from marine microalgae.
Chem. Eng. J. 215-216: 929–936.
Básaca-Loya, G.A., M.A. Valdez, E.A. Enríquez-Guevara, L.E. Gutiérrez-Millán and M.G. Burboa. 2009. Extraction and
purification of B-phycoerythrin from the red microalga Rhodosorus marinus. Cienc. Mar. 35: 359–368.