Microalgae Products

Tailored production of the diatom Phaeodactylum tricornutum results in algae biomass with a high content of polyunsaturated fatty acids such as the omega-3 fatty acid 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. EPA for example plays an important role in human cardiovascular and inflammatory diseases like rheumatoid arthritis and multiple sclerosis.

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. 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.

Diatoms (rock algae) use (chryso-)laminarin as energy and carbon reservoirs. The polysaccharide is a 1,3/1,6-b-d-glucan that can be used in the food, animal feed and agricultural sectors. Laminarin can also be found in the cell wall of many fungi, including pathogenic species. Since contact with laminarin induces the immune system of vascular plants, the polysaccharide is suitable as plant strengthener. According to the literature, the application of laminarin can reduce infections with Botrytis cinerea or Plasmopara viticola in grapevines by 55 or 75 percent [1]. Laminarin also has an immunomodulatory effect in vertebrates. The immune system in the digestive tract in particular reacts to the contact with laminarin [2].

The MIATEST project is examining the use of laminarin as a biostimulant in viticulture in collaboration with the Landesversuchsanstalt für Wein- und Obstbau Baden-Württemberg and its application in nutrition at the Hohenheim University. To this end, Fraunhofer IGB is examining laminarin production strains, developing a two-step production process and producing laminarin-rich algae biomasses for test purposes.

In addition, laminarin is the subject of the EU-funded MAGNIFICENT BBI project, which is examining the provision of ingredients from microalgae for food, feed and cosmetics. The use of laminarin in juvenile fish rearing is currently being investigated.

Literature

[1] Aziz, A. et al. (2003) Laminarin elicits defense responses in grapevine and induces protection against Botrytis cinerea and Plasmopara viticola. Molecular plant-microbe interactions : MPMI 16, 1118–1128

[2] Stuyven E. et al. (2009) Effect of β-glucans on an ETEC infection in piglets. Spec. Issue 8th Int. Vet. Immunol. Symp. 128 (1–3), 60–66

In the food sector, the high content of omega-3 fatty acids makes algae an ideal alternative to fish – a worthwhile option given the overfishing of the world’s oceans. Potential applications and nutritional parameters for the microalga Phaeodactylum tricornutum have already been investigated in a project conducted in collaboration with the Institute of Nutritional Medicine at the University of Hohenheim in Stuttgart.

Analyses showed that dried microalgae contain not only a protein content of nearly 50 percent by dry weight but also significant amounts of the long-chain omega-3 fatty acid eicosapentaenoic acid, or EPA for short. According to an initial study by the University of Hohenheim, microalgae are suitable for meeting the daily requirement for omega-3 fatty acids. They also contain water-soluble dietary fiber, which is important for gut health, as well as vitamin E and carotenoids.

By adjusting the culture conditions in the Fraunhofer IGB photobioreactor, the composition of the ingredients can be controlled. If the algae are supplied with sufficient nutrients, they produce particularly high levels of EPA. If the algae grow under nutrient-limited conditions, they produce more dietary fiber.

Producing food from algae requires no arable land and less water. The single-celled organisms can be cultivated under controlled conditions in closed, vertical photobioreactors – independent of seasonal or climatic factors.

Pest-repellent active ingredients from microalgae and cyanobacteria are suitable as ecologically compatible, biologically based plant protection products.

For applications in the organic cultivation of cabbage or in organic viticulture, we have developed processes for the production of microalgae with repellent or antifungal activity in cross-departmental cooperation.

Use of astaxanthin from H. pluvialis

The red pigment astaxanthin is produced with the algae Haematococcus pluvialis. Astaxanthin is used as a supplement in aquaculture in fish- and shrimp-feed in order to enhance the pink color of shrimp, salmon and trout meat. Astaxanthin belongs to the carotenoids and its chemical structure is similar to beta-carotene. Numerous scientific publications attest astaxanthin with a higher antioxidative potential than vitamin E.

It has also beneficial properties for both the cardiovascular system and human eye function. Hence astaxanthin, in the form of capsules, is taken as a dietary supplement, mostly in Japan and the USA, but also increasingly in Europe.

A further application of astaxanthin is as a red pigment by the cosmetics industry. Fraunhofer IGB can produce astaxanthin economically in photobioreactors specifically designed for mass cultivation of algae. The production process is scalable and can be dimensioned according to customer-specific applications.

We provide the scientific know-how to produce large quantities of Haematococcus algae biomass with a high astaxanthin content.

Scale-up in FPA reactors

The flat-panel airlift (FPA) reactor enables us to produce microalgae or their highly valuable products in a cost effective economic way. In a first cultivation step Haematococcus pluvialis is produced semicontinously in FPA-reactors. In a second batch cultivation step under high light intensities astaxanthin is produced. In the pilot plant up to 40 reactor modules were jointly operated for production of algal products in the range of several kilograms.

High biomass concentrations

In autumn 2002, biomass growth rates of up to 0.25 g TS l^-1 d^-1 at cell concentrations of up to 2.5 g TS l^-1 were achieved in the newly developed FPA reactor on the Stuttgart site. These are the highest values ever achieved for Haematococcus pluvialis due to the good light distribution in the photobioreactor. The formation of astaxanthin is induced by high light intensities (direct sun), nutrient deficiency or inductors such as acetate and table salt. If these factors are taken into account in the batch process, the cell weight increases by a further factor of three to four, while the intracellular astaxanthin content reaches up to five percent of the dry cell weight.

Under outdoor conditions, biomass concentrations of Haematococcus pluvialis of up to 10 g TS l^-1 were achieved in the FPA reactor. This high cell density is an important prerequisite for industrial astaxanthin production.

Microalgae offer a high protein, carbohydrate or lipid content, depending on growth conditions. Fast growing microalgae have a high protein content with a favorable distribution of essential amino acids. Many microalgae have the ability to produce substantial amounts (e.g. 20 – 70 percent dry cell weight) of triacylglycerols (TAGs) or starch as a storage product when under stress and growing slowly, and simultaneously high light intensities are available.

Storage lipids as fuel

In screening tests at Fraunhofer IGB various algae were tested for their ability to produce storage lipids under the conditions of a flat panel airlift (FPA) reactor. Lipid content increased up to 70 percent of dry cell weight and starch contents up to 60 percent are achievable. Under these conditions mainly monounsaturated fatty acids with 16 and 18 carbons were synthesized. Lipid productivity was not specific for a certain strain but depended largely on the light intensity per cell.

Starch for the production of fuels or basic chemicals

Starch can be used as sugar feedstock for miscellaneous biotechnological processes for biofuels or biobased chemicals.  Fraunhofer IGB has developed a two-stage process for production of starch-rich microalgae, which has been established under outdoor conditions as well as scaled up to pilot scale in the range of 100 kg dry biomass.

Due to the limited availability of fossil resources, it is becoming increasingly important for the textile industry to identify and develop alternative raw materials for the production of fibers used in textiles.

In the AlgaeTex research project, various polymers were produced that are intended to consist of the highest possible proportion of algae-based fatty acids. The goal was to develop melt-spinnable polyesters to enable their widespread use in the textile industry.

“Green” hydrogen (H₂), produced through the electrolysis of water using renewable energy, is considered a key element of the energy transition. In two latest projects, Fraunhofer IGB has taken a new approach to producing this climate-neutral energy carrier and industrial feedstock: Using biotechnological processes, such as microorganisms (purple bacteria) or microalgae, the goal is to generate biohydrogen from waste streams like waste wood or wastewater.

In the SmartBioH₂ project, a novel concept based on direct photolysis was chosen for hydrogen production using microalgae. By immobilizing the algae and using a special reactor setup, the oxygen produced as a by-product along with hydrogen by the algae is to be efficiently separated to a partial pressure of less than 100 ppm in the reactor gas volume. The continuous removal of oxygen to a very low oxygen partial pressure in the reactor is crucial for the functioning of the process. If the oxygen content in the system is too high, the extremely sensitive enzymes needed for hydrogen production are being oxidized.

After setting up the experiment in the laboratory, hydrogen was successfully measured in short-term experiments. However, the system has not yet been optimized. In particular, the method for immobilizing the microalgae still needs to be further developed. The chosen concept for hydrogen production with microalgae can be easily scaled up and is planned to be applied on a pilot scale.

In a second laboratory setup, the separation of oxygen from the gas phase was also successfully tested, using a known oxygen separation method. With this setup, it was possible to reduce the oxygen partial pressure to below the critical threshold for hydrogen production within a short time.