J Supercrit Fluids. 2016 Oct; 116:126-131
Supercritical fluid extraction from microalgae with high content of LC-PUFAs. A case of study: Sc-CO2 oil extraction from Schizochytrium sp.
Zinnai A., Sanmartin C., Taglieri I., Andrich G., Venturi F.
Department of Agriculture, Food and Environment (DAFE), University of Pisa, Via del Borghetto, 80 – 56124 – Pisa (Italy).
Among the different kinds of marine sources, microalgae are a potential source of triacylglycerides which may contain high amounts of LC-PUFAs such as w-3 fatty acids EPA and DHA.
For the extraction of oil from microalgae, Sc-CO2 is regarded with interest being safer than hexane and offering a negligible environmental impact, a short extraction time and a petroleum-free final product.
In such a contest, a mathematical model able to describe the kinetics of an SFE process was applied to the extraction with Sc-CO2 of lipids from Schizochytrium sp., a marine microalga characterized by a particularly high content of LC-PUFAs, and a very high concentration of DHA.
The aim of this paper was to examine the effect of operating conditions on the kinetics of the SFE, on process yields and on the fatty acid composition of lipid extracts, also in comparison with the conventional extraction by percolation with n-hexane.
In recent years, many plant-derived natural products have been suggested to be a source for bioactive compounds (1) and actually the marine environment is considered a rich, underexploited source of high added-value compounds (2). Among the different kinds of marine sources, macroalgae (seaweeds) and microalgae are probably the two groups of marine organisms that have attracted most attention for their potential as industrially feasible natural sources of bioactive ingredients that can be used by the food industry for the development of functional foods with scientifically sustained claims (3, 4, 5). In particular, microalgae are a potential source of triacylglycerides (TAG) which may contain high amounts of LC-PUFAs such as w-3 fatty acids EPA and DHA (6).
As described in depth by Richmond (7), microalgae are present in all earth existing ecosystems, not just aquatic but also terrestrial, representing a big variety of species (it is estimated that more than 50.000 species exist, but among them only almost 30.000 have been studied and analyzed) living in a wide range of environmental conditions. Furthermore, the possibility of culturing microalgae in non arable lands as well as metabolism modulation following some stresses application, make them an attractive feedstock for industrial production (8, 9, 10).
Closely related to this point, the sustainability of the processes employed to extract and to purify the bioactive compounds is of the utmost importance (3). Today, not only is efficiency of the extraction techniques sought by extracting bioactives with the highest possible extraction yield and associated bioactivity, but the development of environment-friendly extraction processes is also preferred over conventional extraction protocols (11).
One alternative to traditional extraction process (i.e. by using organic solvents such as n-hexane) of target compounds from microalgae is to carry out the extractions using supercritical (SFE) carbon dioxide (Sc-CO2). In particular, Sc-CO2 is regarded with interest as an industrial process, being considered a safe, non-flammable solvent that offers a certain extent of tunable selectivity, mild operating conditions, no environmental impact, shorter extraction time and a high-quality final product without any trace of toxic solvent (12, 13, 14).
In such a contest, a mathematical model able to describe the kinetics of an SFE process was applied to the extraction with Sc-CO2 of lipids from Schizochytrium sp., a marine microalga characterized by a particularly high content of LC-PUFAs, and a very high concentration of docosahexaenoic acid (DHA; 22:6, n-3) (15, 16).
The aim of this paper was to examine the effect of operating conditions on the kinetics of the SFE, on process yields and on the fatty acid composition of lipid extracts (Figure 1).
Figure 1. Graphical abstract of the proposed extraction method.
This research is part of a wider experimental project involving the SFE of bioactive lipids from microalgae and having two main objectives: (a) to test the validity of the mathematical model proposed to describe the kinetics of extraction, the knowledge of which is required for process optimization and scaling-up; (b) to evaluate the economical feasibility of such a process.
On the basis of the results obtained (17), the kinetic model seems suitable, even if for its generalization more information is needed. While ScCO2 and n-hexane have been shown to be comparable on the basis of the theoretical process yield (t®∞) and the fatty acid composition of the extracts, SFE proved to be much faster.
Different extracts show an high ratio LC-PUFAw-3/LC-PUFAw-6 and C22:6w-3/C20:5w-3 DHA/EPA, according to nutritional requirements. An high ratio LC-PUFAw-3/LC-PUFAw-6 is strongly suggested for European consumers that generally show a right dietary intake of w-6 fats from different vegetable oils, but their consumption of LC-PUFAw-3 appears usually too low.
The extracted lipids show a fatty acid profile substantially in agreement with those reported in literature for such kind of oil, even if the fatty acid composition of microalgae is reported to be highly changeable as a function of the selected strain, the culture conditions adopted as well as the stage of development evaluated (9, 10).
Furthermore, no particular differences were found in the fatty acid profiles of extracts when different SFE were performed, also in comparison with the traditional extraction with n-hexane.
Although both solvents gave process yields lower than expected, probably as a result of some losses in the most polar lipid fractions, Schizochytrium sp. is confirmed as a good source of LC-PUFAs and, in particular, of DHA.
 Brusotti G., Cesari I., Dentamaro A., Caccialanza G., Massolini G. 2014 Isolation and characterization of bioactive compounds from plant resources: the role of analysis in the ethnopharmacological approach, Journal of Pharmaceutical and Biomedical Analysis 87: 218–228.
 Hernandez-Ledesma B., Herrero M. 2014 Bioactive Compounds from Marine Foods, Wiley Blackwell, Chichester, UK.
 Herrero M., del Pilar Sánchez-Camargo A., Cifuentes A., Ibáñez E. 2015 Plants, seaweeds, microalgae and food by-products as natural sources of functional ingredients obtained using pressurized liquid extraction and supercritical fluid extraction, Trends in Analytical Chemistry 71: 26–38.
 de Jesus Raposo M.F., de Morais R.M., de Morais A.M. 2013 Health applications of bioactive compounds from marine microalgae, Life Science 93: 479–486.
 Holdt S.L., Kraan S. 2011 Bioactive compounds in seaweed: functional food applications and legislation, Journal of Applied Phycology 23: 543–597.
 Stonik V.A., Fedorov S.N. 2014 Marine low molecular weight natural products as potential cancer preventive compounds, Marine Drugs 12: 636–671.
 Richmond A. 2004 Handbook of microalgal culture: biotechnology and applied phycology. Blackwell Science Ltd.
 Maadane A., Merghoub N., Ainane T., El Arroussi H., Benhima R., Amzazi S., Bakri Y., Wahby I. 2015 Antioxidant activity of some Moroccan marine microalgae: Pufaprofiles, carotenoids and phenolic content, Journal of Biotechnology 215: 13–19.
 Suh S.-S., Kim S. J., Hwang J., Park M., Lee T.-K., Kil E.-J., Lee S. 2015 Fatty acid methyl ester profiles and nutritive values of 20 marine microalgae in Korea, Asian Pacific Journal of Tropical Medicine 191-196.
 Singh P., Kumari S., Guldhe A., Misra R., Rawat I., Bux F. 2016 Trends and novel strategies for enhancing lipid accumulation and quality in microalgae, Renewable and Sustainable Energy Reviews 55: 1–16.
 Chemat F., Vian M.A., Cravotto G. 2012 Green extraction of natural products: concept and principles, International Journal of Molecular Science 13: 8615–8627.
 Zinnai A., Venturi F., Sanmartin C., Andrich G. 2012 A simplified kinetic model to describe oil extraction from different substrates by supercritical CO2, American Journal of Analytical Chemistry 3: 939-945.
 Souza Machado B.A., Gambini Pereira C., Nunes S.B., Ferreira Padilha F., Umsza-Guez M.A. 2013 Supercritical fluid extraction using CO2: main applications and future perspectives, Separation Science and Technology 48: 2741–2760.
 Yeng H.-W., Yang S.-C., Chen C.-H., Jesisca, Chang J.-S. 2015 Supercritical fluid extraction of valuable compounds from microalgal biomass, Bioresource Technology 184: 291-296.
 Ganuza E., Benítez-Santana T., Atalah E., Vega-Orellana O., Ganga R., Izquierdo M.S. 2008 Crypthecodinium cohnii and Schizochytrium sp. as potential substitutes to fisheries-derived oils from seabream (Sparus aurata) microdiets, Aquaculture 277: 109–116.
 García-Ortega A., Kissinger K.R., Trushenski J.T. 2016 Evaluation of fish meal and fish oil replacement by soybean protein and algal meal from Schizochytrium limacinum in diets for giant grouper Epinephelus lanceolatus, Aquaculture 452: 1–8.
 Zinnai A., Sanmartin C., Taglieri I., Andrich G., Venturi F. 2016 Supercritical fluid extraction from microalgae with high content of LC-PUFAs. A case of study: Sc-CO2 oil extraction from Schizochytrium sp., Journal of Supercritical Fluids 116: 126-131.