Valuable and Bioactive Compounds

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Only plants synthesize PUFAs (linoleic, linolenic, arachi donic, and eicosapentaenoic acid). Therefore, microalgae supply whole food chains with these vital components. Microalgal PUFAs have a very promising biotechnologi cal market both for food and feed.

For lipid based cosmetics like creams or lotions, ethanolic or supercritical CO2 extracts of microalgal bio mass are also gaining commercial importance, because they provide both nourishing and protecting effects to the skin.

Table 1 Biotechnological application of the most exploited microalgae

Product and

Application Content (% of DW) Status Microalga

Table 1 Biotechnological application of the most exploited microalgae

^-Carotene

10

Established

Dunaliella

Health food, food and

Established

Arthrospira (Spirulina), Chlorella

feed supplement

Feed (aquaculture)

Established

Microalgae as feed in aquaculture (e.g., Isochrysis, Nannochloropsis, Pavlova, Tetraselmis, Monodus)

Astaxanthin

3-5

Emerging

Haematococcus

Xanthophylls (lutein,

0.5-1

Developing

Scenedesmus

zeaxanthin)

PUFAs

Developing

Porphyridium, Isochrysis, Nannochloropsis

Polysaccharides

Developing

Porphyridium

Microalgal polysaccharides are pharmacologically important. For example, certain highly sulfated polysac charides trigger either a cellular or humoral stimulation of the human immune system. Effective polysaccharide fractions have been found mainly in cyanobacteria; how ever, compounds from green and red algae are also efficient.

Due to their phototrophic life, microalgae experience high oxygen and radical stresses. Their protective mechanisms, based on highly effective oxygen radical scavengers, prevent the accumulation of free radicals and reactive oxygen species (e.g., superoxide anion, hydroxyl radical, or singlet oxygen), thus avoiding cell damage. For example, the antioxidative potential of Spirulina can increase 2.3 fold during O2 stress. Of parti cular note is the high content in lipophilic scavengers, such as carotenoids, especially ft carotene and a toco pherol; minerals and trace elements with an antioxidative effect, such as zinc and selenium; and enzymatic scaven gers, such as catalase, superoxide dismutase, and peroxidase, and vitamins C and E.

The most impressive demonstration of the ability of microalgae to produce highly effective bioactive compounds are toxins, which in algal blooms become dangerous to animals and humans, especially if it occurs in drinking water reservoirs (found especially in Microcystis, Anabaena, and Aphanizomenon).

The extensive screening of microalgae and cyanobac teria for new substances with biological activities, undertaken in many laboratories and companies, have revealed the following effects:

• cytotoxic activity which is important in anticancer drugs,

• antiviral activities,

• antimicrobial activity to find new antibiotics, and

• antifungal activity in extracts of cyanobacteria.

Because phototrophic microalgae can be cultivated under strictly controlled conditions, they are the ideal choice to incorporate stable isotopes from inorganic C , H , and N sources. Various biochemicals labeled by stable isotopes are used for scientific purposes (molecular structure or physiological investigations), as well as for clinical pur poses (gastrointestinal or breath diagnosis tests).

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