Short CommunicationComparative study of lipid extraction from microalgae by organic solvent and supercritical CO2
Highlights
► The microalgal crude lipids content determined using the mixed solvent with ultrasonic method was 44.7 wt.%. ► Triglyceride content obtained by the mixed solvent method was 15.6 wt.%. ► The extraction yield was improved by cell disruption prior to extraction, and the highest triglyceride extraction yield of 98.7% was observed using the supercritical fluid extraction (SFE) method with bead-beating. ► The results indicate that the SFE method is effective and provides higher selectivity for triglyceride extraction though the total lipid extracted was less than that using solvent extraction.
Introduction
Microalgal biofuels possess enormous potential and offer a breakthrough solution to both energy security and global warming concerns. Significant amounts of venture capital, private equity funds, and human talent have been allocated to numerous algae startups/developments. The race to develop the first commercial-scale microalgal biofuel production system that can generate substantial investor returns and create a new transportation fuel infrastructure model is currently being conducted. Most people involved in this emerging technology agree that the commercial economics of microalgal biofuels are extremely challenging, highly variable, and subject to dynamic, speculative, and volatile commodity markets.
Microalgal lipids, commonly referred to as crude lipids or total fatty acids of microalgae, are extracted and then arranged by transesterification during the production of microalgal biofuels. The key processes involved in biodiesel production from microalgae include cultivation, harvest, lipid extraction, and transesterification of the lipids. Various extraction methods have been reported for microalgal lipids, including traditional solvent extraction (National Algal Biofuels Technology Roadmap, 2009), accelerated solvent extraction (Schafer, 1998), subcritical water extraction (Herrero et al., 2006), supercritical CO2 or methanol (Herrero et al., 2006, Chung, 1999), and milking (Hejazi et al., 2002).
Conventional methods for extracting lipids include hexane extraction and vacuum distillation, which use flammable or toxic solvents, cause adverse health and environmental effects. They may also cause the PUFAs to deteriorate due to high-temperature processing. Supercritical fluid extraction (SFE) is a promising process for extracting lipids containing labile PUFAs because the extraction method can be conducted at a low temperature. Moreover, supercritical fluid extraction offers new opportunities for using CO2, which is a non-toxic, non-flammable, inexpensive, and environmentally friendly solvent (Létisse et al., 2006). Supercritical CO2 extraction studies were performed involving microalgae (Mendes et al., 2003, Reverchon and Marco, 2006). Mendes et al., 1995, Mendes et al., 2003 conducted extraction at a pressure range of 170–306 bar, with a temperature range of 30–60 °C; the best extraction yield for crude lipids was under a pressure of 306 bar and a temperature of 60 °C.
In this study, the efficiency of Pavlova sp. lipid extraction using organic solvents and supercritical CO2 was compared. The extraction selectivity is evaluated by analyzing the fatty acid methyl ester (FAME) of the crude lipids.
Section snippets
Raw material
The dark-brown and spray-dried powder of Pavlova sp. was obtained from Dr. Jun-Yao Chu, and used without further purification. Industrial grade organic solvents were obtained from Echo Chemical Co., Ltd., Taiwan, ROC. Carbon dioxide was supplied by Chiah Lung Enterprise Co., Ltd., Taiwan, ROC. They were all used for microalgae extraction without further purification.
Because microalgae have rigid cell walls, and the lipids are within the cell walls, a bead-beating (Lee et al., 2010) machine was
Crude lipids and FAME
This study used dry microalgal powder for solvent extraction, and the liquid or paste type extracts were weighed and examined using an optical microscope to ensure the microalgae was completely separated from the extracts.
The crude lipids yield obtained by Soxhlet extraction of Pavlova sp. was 18.5 wt.% with 100 h extraction time. The FAME yield was obtained from transesterification of the crude lipids and then quantified by GC with an internal standard. The FAME yield was 9.8 wt.% for Pavlova sp.
Conclusions
Considering the extraction efficiency of microalgal lipids for biodiesel application, the FAME extraction yield was a more accurate index compared to the crude lipids yield. Comparing the extraction yield of microalgal powder for different methods, the result of the ethyl acetate/methanol mixed solvent method (98.1%) was better than that of the Soxhlet method (61.6%). The FAME extraction yield obtained by the SFE method with bead-beating microalgae (98.7%) was better than that of other
Acknowledgements
The authors acknowledge the financial support provided by the Bureau of Energy, MOEA, Taiwan, ROC. We thank Dr. Jun-Yao Chu for providing the Pavlova sp. powder.
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