Cell disruption and extraction processes for the cascade utilization of microalgae biomass

Due to the great diversity of ingredients and the different cell wall characteristics of various species of microalgae, it is necessary to carry out selective processing of the biomass in order to effectively extract the high-quality nutrients. The objective of the joint research network “Microalgae – Integrated Use for Food and Feed” in the Baden-Württemberg Bioeconomy Research Program is to utilize various fractions as completely as possible, in interconnected and cascade use, in order to develop sustainable processes for the bioeconomy.

Processing of algae constituents

Special requirements apply to processing in the extraction of valuable compounds from algae biomass and the further use of the residual biomass, especially in cascade utilization. Basically the chemical character and the market specifications, for example the required degree of product purity, determine the processing technique. Further requirements are avoiding, as far as possible, an energy-intensive drying step as well as ensuring gentle extraction that both maintains the functionality and permits the extraction of further cell components.

Working together with the partners in the research network, three strains of microalgae (Phaeodactylum tricornutum, Chlorella vulgaris and Nannochloropsis spec.) were selected that differ fundamentally in cell size, formation of the cell wall and biomass composition. By combining successive extraction processes in various sequences, the objective is to obtain in particular the principal fractions consisting of proteins, polar membrane lipids with omega-3 fatty acids as well as nonpolar triglycerides sequentially from the microalgae biomass – in addition to the high-value components such as carotenoids.

Selective and targeted extraction

The technique called “Pressurized Liquid Extraction” is mainly employed here; this also permits extraction using wet biomass, as well as extraction by means of supercritical fluids (SCF). In order to increase the polarity of supercritical fluids, cosolvents such as ethanol can be employed. This results in a selective extraction of polar glycolipids containing eicosapentaenoic acid EPA; 20:5 ω-3. The different extraction behavior without and with a cosolvent was also used specifically for the sequential, selective extraction of nonpolar triglycerides, carotenoids and polar glycolipids. Currently the process parameters are being optimized with the aim of obtaining fractions that are then examined by the research partners in regard to an application in the food sector. After extraction of the lipophilic valuable compounds the aim is to separate the proteins from the residual biomass, so as to make them available for the production of novel foods by project partners. The residual biomass is suitable for animal feed production.

Recovery of eicosapentaenoic acid (EPA) and fucoxanthin

Tailored production of the diatom Phaeodactylum tricornutum results in algae biomass with a high content of polyunsaturated fatty acids such as eicosapentaenoic acid (EPA, 20:5 ω-3) and accessory pigments such as fucoxanthin. These ingredients have various health-promoting and anti-oxidative properties, which is why the recovery of the relevant extracts is of great interest to the food, feed and cosmetics industries.

As part of the Bioeconomy Baden-Württemberg project, the diatom P. tricornutum was cultivated in flat-panel airlift reactors (FPA reactors) in semi-continuous operation at different light intensities. The influence of light availability on the composition of biomass with regard to EPA and fucoxanthin content was investigated. In particular, the fucoxanthin content showed a significant dependence on the relative light availability, i.e. the ratio of photon flux (on the reactor surface) to total biomass in the reactor and time (in µmol photons g^-1 of dry mass s^-1). In combination with an optimized and controlled supply of nutrients, we were able to achieve fucoxanthin contents of more than 2 percent (w/w) in terms of dry weight using the FPA photobioreactor [1]. After mechanical cell disruption, both EPA and fucoxanthin can be recovered by means of pressurized liquid extraction (PLE) using suitable organic extraction solvents with yields of over 90 percent. At the Institute of Clinical Nutrition at the University of Hohenheim the extracts were investigated with regard to their nutritional properties: they have a high anti-oxidative and anti-inflammatory capacity [2].

With completion of the project there is a matrix of methods available for the processing of algae biomass that can be transferred to biomass of various algae species, with a different material composition in each case and with different target fractions. This contributes a big step towards using microalgae holistically for nutritional purposes as well as an important step towards a biobased economy.

The extracts obtained provide the food, feed and cosmetics industries with natural extracts that have health-promoting and coloring properties, which can then be converted into the corresponding products.

On behalf of interested companies, we will be glad to investigate how you can use the extracts or provide sample quantities.

1. Derwenskus, F.; Hardtmann, M.; Frick, K.; Gille, A.; Schmid-Staiger, U.; Schließmann, U.; Hirth, T. (2017) Einfluss der relativen Lichtverfügbarkeit auf den EPA- und Fucoxanthingehalt von P. tricornutum bei semi-kontinuierlicher Kultivierung im FPA-Reaktor. DECHEMA 10. Bundesalgenstammtisch 2017, Merseburg
2. Derwenskus, F.; Neumann, U.; Gille, A.; Schmid-Staiger, U.; El-Benna, J.; Schließmann, U.; Bischoff, S.C.; Hirth, T. (2017) Production of fucoxanthin and EPA with P. tricornutum-antioxidant extracts for food and cosmetic applications. AlgaEurope, 5.12.2017 – 7.12.2017, Berlin