Eicosapentaenoic acid from algae

Eicosapentaenoic acid (20:5, EPA) belongs to the omega-3 fatty acid class. These are highly unsaturated fatty acids with a special positioning of the first double bond. Many organisms cannot synthesize omega-3 fatty acids, they are essential. In humans, too, they must be supplied during child development.

Omega-3 fatty acids serve as a precursor for important tissue hormones. A lack of omega-3 fatty acids leads to an increased risk of civilization diseases such as heart attack and stroke. An anti-oxidative and thus cancer-protective effect of omega-3 fatty acids is also being discussed. The main source of EPA in the diet is fish oil from marine cold-water fish. Low fish consumption leads to an undersupply in broad sections of the population. Fish oil is also used for the industrial production of omega-3 fatty acids. The disadvantages here are the perceived bad taste and the accumulation of toxic heavy metals, especially mercury, from the environment. Therefore, other sources for the technical production of EPA are being intensively sought.

The marine microalgae Phaeodactylum tricornutum UTEX 640 combines all important criteria for an industrially usable EPA producer: fast growth, high EPA content, absence of antagonistic substances such as docosahexaenoic acid (22:6, DHA) and a purely photo-autotrophic production, only using sunlight as energy and carbon dioxide as a carbon source.

Phaeodactylum tricornutum is cultivated in a photobioreactor specially developed at the Fraunhofer IGB, the flat panel airlift (FPA) reactor. The FPA reactor is characterized by an optimal light supply to all algae cells as a result of targeted flow control. The production from two deep-drawn PVC half-shells guarantees low production costs.

Under laboratory conditions, all relevant operating parameters and especially medium components were examined in detail. Urea as nitrogen source, an average gassing rate of 0.66 vvm (volume per volume per minute) and a relatively low carbon dioxide concentration of 1.25 percent (v/v) proved to be optimal. Thanks to this mode of operation, which is adapted to the organism, productivities of 2.35 grams of dry substance per litre and day are already achieved at 1 000 μE·m^-2·s^-1 (E=Einstein, half sunlight intensity). The biomass concentration in the reactor rises to 26 grams of dry matter per litre. At medium light intensities, up to 10.6 percent of the incident light energy is converted into biomass. This is 35 percent of the theoretically possible maximum value.

EPA production in the field

From the beginning of May to the end of October, ten production reactors were operated in parallel in the open air (Stuttgart institute site). The modular design allows each reactor to be controlled separately, allowing process control to be adapted quickly and efficiently to field conditions. With a yearly average of 530 mg dry substance per litre per day, productivity was achieved with a north-south orientation (reactor flat sides facing north and south) and 80 cm distance between the individual reactors. In June, with good weather conditions, these values were again almost 40 percent higher, reaching 730 mg dry matter per litre and day.

The EPA content in the laboratory and in the field is a constant 5 percent of the total organic dry matter. This results in EPA productivity in the order of 27 mg EPA per litre per day on an annual average. An EPA content of 30 percent of the total fatty acids simplifies the purification process.

High growth rates, a high EPA content and low investment costs for the reactor provide the prerequisites for industrial photo-autotrophic production of omega-3 fatty acids using microalgae.