BIOTECHNOLOGY - V. H. Gerasymenko - 2006

Part II. Specialized Biotechnologies

Chapter 21. BIOTECHNOLOGY OF PROTEIN PRODUCTION

21.8. PRODUCTION OF SINGLE-CELL PROTEIN FROM ALGAE

Single-Cell Algae represent a significant reserve of protein for human consumption and animal feed.

Unlike the cultivation of Bacteria and Yeasts, microalgae cultivation is not a continuous process because it relies on Photosynthesis. The efficiency of algal biomass production depends on lighting conditions, Temperature, and the COMPOSITION OF THE nutrient medium, while the process itself requires large volumes of Water.

Single-cell algae can be cultivated both under natural conditions in fresh, saline, and alkaline water bodies, and in specialized phytobiological reactors using artificial media and livestock wastewater.

Large-scale cultivation of green algae is carried out in many countries. For instance, in Japan, by propagating the unicellular alga *Chlorella* in freshwater reservoirs, it was possible to obtain about 16 tons of protein per hectare of water surface. For comparison, only 471 kg of protein can be obtained from 1 hectare of peanut crops.

Scientists have developed phytobiological reactors designed for marine algae cultivation. In simplified terms, such a Reactor is a Glass or plastic tube in which a specific species of algae is grown. Its density is maintained at an optimal level using computers and microprocessors, and biomass yield is regulated According to the intensity of solar radiation. Such a reactor can be constructed above the sea. It can be used to produce large quantities of oxygen required by various industries. Scientists have calculated that up to 14% of solar energy can be utilized in such a reactor. For comparison, plants in a field absorb only 1% of the energy.

At Oregon State University (USA), studies were conducted on cultivating microalgae—*Chlorella*, *Spirulina*, and *Scenedesmus*—on manure wastewater collected from pig farms through pipelines into a special basin where specific lighting and temperature conditions were maintained. The best growth of *Chlorella* was observed at a temperature of 35 °C and a nitrogen content of 250 mg per liter of medium.

In the former Soviet Union, a technology was also developed for growing *Chlorella* on wastewater from pig-breeding complexes, with the subsequent use of the biomass as animal feed.

In Ukraine, during the 1950s and 1960s, attempts were made to cultivate *Chlorella* under production conditions. Experience in cultivating this alga showed that it is advisable to propagate it as a feed additive for livestock and poultry. However, significant success in utilizing *Chlorella* was not achieved due to the complexities associated with biomass concentration and scale-up.

A more promising source for protein production is the blue-green alga *Spirulina* (*Spirulina platensis*, *S. maxima*), which propagates better on artificial media compared to *Chlorella*.

The European Commission has evaluated several efficient and promising systems for cultivating *Spirulina* biomass for feed and food purposes: the Montedison tubular-cylindrical-channel system; an open tubular system with propagation in trays for industrial settings; and the E₁ – E₆ system for biomass production on wastewater.

Growth intensity, The rate of biomass accumulation, and its chemical composition are significantly influenced by temperature, lighting, nutrient medium composition, and especially the concentration of nitrogen in it. In all algae, increasing the nitrogen Nutrition level from 8 mg/L to 450 mg/L resulted in an increased rate of biomass accumulation and a rise in protein content within the biomass from 8% to 54%.

The optimal temperature for *Spirulina* cultivation is 30–42 ^oC. With a further increase in temperature, the growth rate of the alga and the protein content in the biomass decline.

When *Spirulina* was cultivated under conditions of insufficient solar radiation and on foggy days, its growth rate dropped sharply.

Unlike yeasts and some other microorganisms, *Spirulina* can intensively reproduce across a wide range of mineral concentrations. Zarrouk's medium is most commonly used for *Spirulina* cultivation, containing a significant amount of sodium bicarbonate (16.8 g/L), which maintains a pH of around 9.5.

Genetic improvement of *Spirulina* strains can significantly enhance growth intensity and biomass accumulation. In Mexico, Introduction/32.html">Genetic Engineering Methods were used to obtain strains capable of growing on various alkaline media under artificial conditions. The biomass yield of *Spirulina* reached 10–20 tons per hectare.

Analyzes of *Spirulina* samples obtained in laboratories and collected from the wild, conducted at the French Institute of Petroleum as well as in Japan, Italy, and Mexico, showed that it contains an average of 65% protein (significantly more than soybeans), 19% CARBOHYDRATES, 6% pigments, 4% Lipids, 3% fiber, and 3% ash. Its cell walls are more easily digested compared to *Chlorella* and *Scenedesmus*.

Under conditions of balanced biogenic macro- and microelements, along with an adequate supply of heat and light, *Spirulina* can synthesize organic matter with a high protein content (87–91%), including 60–70% true protein, 21–27% non-protein nitrogenous compounds, 8–10% nitrogen-free extractives, and 6–8% ash. In terms of essential amino acid balance, *Spirulina* occupies an intermediate position between plant- and animal-derived Proteins (Kyryiachenko S. P., 1997).

Three types of products derived from *Spirulina* can be used for feed and food purposes: a paste-like suspension obtained after Separation; dry dehydrated biomass produced by lyophilization, drum drying, or spray drying in chambers; and dry mass obtained after Fermentation and extraction of easily soluble substances.