Extraction of fatty acids from dried freshwater algae using accelerated solvent extraction

Authors: Mulbry, Walter; Kondrad Ingram, Shannon; Buyer, Jeffrey; Luthria, Devanand - Dave

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2009
Publication Date: 7/4/2009
Citation: Mulbry III, W.W., Ingram, S.K., Buyer, J.S., Luthria, D.L. 2009. Extraction of fatty acids from dried freshwater algae using accelerated solvent extraction. Journal of the American Oil Chemists' Society. 86:909-915.

Interpretive Summary: There is considerable interest in the coupling of biological waste treatment processes to bio-energy production. One frequently mentioned possibility is to use an algae-based treatment process to treat agricultural wastewater or manure and to extract fatty acids from the harvested algal biomass. Although algae-based wastewater treatment processes have been in existence for over 30 years, the historically low price of petroleum has inhibited efforts to use the resulting biomass as an energy feedstock. Increasing costs of petroleum and mandated targets for bio-based energy production has stimulated renewed interest in this area. Determination of fatty acid (FA) content in algae is generally conducted by manual extraction with a mixture of the organic solvents chloroform and methanol. Although this method requires very simple equipment, most protocols specify that the samples be freeze-dried and finely ground prior to extraction. In addition, multiple rounds of extraction are usually required for efficient removal of fatty acids. Accelerated solvent extraction (ASE) is a relatively new automated extraction method that has been used to determine total lipid and FA composition in cereal, egg yolk, chicken muscle, corn, and soybean. The objective of this study was to optimize extraction of dried algal biomass and compare total lipid extraction efficiency and the fatty acid profiles of the extracted total lipids with ASE and the conventional method. Our results showed that the ASE and conventional extraction method yielded similar values for FA content after four extraction cycles with a chloroform/methanol solvent mixture. However, the ASE method yielded much higher amounts of FA in the first cycle (85-95% of total extracted) compared to the Folch method (44-55% of total extracted in the first cycle). As expected, the extraction efficiency of the ASE method for FA was dependent on the extraction solvent. Use of a chloroform/methanol solvent mixture yielded higher FA values relative to values from extractions using isopropanol/hexane or hexane alone. Results also showed that FA content values using the Folch method or ASE with chloroform/methanol were not significantly influenced by sample particle size within the size range of 0.1 to 1 mm. These results demonstrate that the ASE method works well with algae from wastewater treatment. In our experience, the ASE method is much easier to use than the conventional extraction method and decreases potential exposure to extraction solvents. Although not the focus of these experiments, it is likely further optimization of the ASE method will allow for the reduction in the volume of solvents needed for efficient FA extraction.

Technical Abstract: A high temperature/pressure extraction method (accelerated solvent extraction)(ASE) and a manual extraction method (modified Folch extraction) were compared with regard to their ability to extract total fat from three samples of air-dried filamentous algae and determine the fatty acid (FA) profile of the extracted oil. The efficiency of extraction of total fat with three solvent combinations (chloroform/methanol, isopropanol/hexane, and hexane) commonly used for total fat extraction was also evaluated using an ASE method. Results showed that the ASE method yielded higher values for total fat content compared to the Folch method, but similar values for FA content and composition were obtained after four extraction cycles with a chloroform/methanol solvent mixture (2:1 v/v). However, the ASE method yielded much higher amounts of FA in the first cycle (85-95% of total extracted) compared to the Folch method (44-55% of total extracted in the first cycle). As expected, the extraction efficiency of the ASE method for FA was dependent on the extraction solvent. FA content values using ASE with chloroform/methanol > isopropanol/hexane > hexane. Results showed that FA content values using the Folch method or ASE with chloroform/methanol were not significantly influenced by sample particle size within the size range of 0.1 to 1 mm.