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Tomato juice is a cost-effective cultivation medium for growing the microalga Euglena.

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By Milthon Lujan

Using tomato juice fortified with essential vitamins (B1 and B12) as a medium to grow the edible microalgae E. gracilis is six times less expensive than using the traditional "KH" medium. This innovative approach could boost the production of E. gracilis as food products and supplements. Credit: Kyohei Yamashita from Tokyo University of Science.
Using tomato juice fortified with essential vitamins (B1 and B12) as a medium to grow the edible microalgae E. gracilis is six times less expensive than using the traditional “KH” medium. This innovative approach could boost the production of E. gracilis as food products and supplements. Credit: Kyohei Yamashita from Tokyo University of Science.

In the quest for sustainable food production, researchers have unveiled an innovative technology for cultivating Euglena gracilis, a single-celled green alga with immense potential as a nutrient-rich food source.

Unlike conventional methods, this innovative approach uses common beverages as a cost-effective nutritional medium, marking a significant step toward achieving global sustainability goals.

Aiming to enhance the efficiency of existing production processes, a team of researchers from Japan conducted experiments to find a promising method for cultivating Euglena in large quantities. As explained in their latest article, the team examined various beverages to find a suitable cultivation medium for Euglena.

The study was led by Assistant Professor Kyohei Yamashita from the Tokyo University of Science (TUS) in collaboration with Dr. Kengo Suzuki and Dr. Koji Yamada from Euglena Co., Ltd., and Professor Eiji Tokunaga from TUS.

The microalga Euglena

Euglena (Euglena gracilis) is a microalga containing chloroplasts that produce organic matter through photosynthesis in well-lit environments, while absorbing organic matter from the surroundings in dark environments. It is known to be rich in nutrients such as vitamins, minerals, amino acids, and essential fatty acids like DHA and EPA. Due to the lack of cell walls, Euglena has a high rate of digestion and absorption, making it an attractive new source of nutritious and health-improving food.

Euglena protein is rich in methionine, a characteristic of animal protein, and its nutritional value is comparable to casein found in milk. Therefore, it is expected to be a solution to the shortage of animal protein due to the effects of climate change and population growth, as well as a production technology for space exploration, which is flourishing these days.

Additionally, Euglena also contains a high percentage of a special type of beta-1,3-glucan called paramylon, known for its immunomodulatory and hepatoprotective effects. Paramylon may also be effective in reducing symptoms of atopic dermatitis, flu, arthritis, and preventing colon cancer. However, existing methods for manufacturing food-grade Euglena are quite complicated.

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Euglena Cultivation

Currently, Euglena can be propagated using both autotrophic and heterotrophic cultivation media. Conventionally, the Koren-Hutner (KH) medium, a higher-yielding heterotrophic medium, is used for cultivation.

However, it requires measuring and mixing 26 different chemicals. Additionally, once the microalgae have reproduced at high densities in large pools, they must be extracted, washed, concentrated, and dried to turn them into food or nutritional supplements. The energy required for these processes accounts for approximately 30% of the total production cost, and the production of Euglena as a food ingredient also incurs other costs, such as land and transportation costs.

The Experiment

Researchers first cultivated Euglena statically with an initial cell density of 4.2 x 103 cells/mL under aerobic conditions for about 10 days. They used the Cramers-Myers (CM) medium, an independent nutritional medium, or the KH medium, a heterotrophic medium. The cell density increased to 106 cells/mL and 107 cells/mL, respectively.

Next, they incubated Euglena with an initial cell density of 1.6 x 104 cells/mL in 13 different beverages, including diluted grape juice (with a juice-to-water ratio of 3:7 or 7:3), pineapple juice, apple juice, sweet wines, diluted carrot juice (with a juice-to-water ratio of 3:7 or 7:3), tomato juice, orange juice, grapefruit juice, prune juice, coconut water, maple water, and a cultivation medium supplemented with essential vitamins B1 and B12 under aerobic conditions.

Cells were cultivated under “light” conditions (26 °C, white light irradiation) or “darkness” (23 °C, no light irradiation).

The Power of Tomato Juice

Among the 13 beverages analyzed in this study, tomato juice emerged as the most promising medium for the cultivation of Euglena gracilis. Surprisingly, the alga reached a cell density of 107 cells per mL, equivalent to conventional heterotrophic media but at only 1/6 of the cost. This also resulted in a change in the appearance of the cultivation medium from red to green after incubation.

Researchers observed that the bright green chloroplasts of Euglena cultivated in tomato juice were tightly packed inside the cells. On the other hand, in juice without tomatoes, the number of chloroplasts was low, and the green color was lighter. These findings suggest that tomato juice is more suitable for Euglena growth than other beverages.

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Moreover, when cultivating Euglena under aerobic conditions using tomato juice diluted with water (at ratios of 3:7, 4:6, or 5:5) and without essential vitamins, it grew approximately 100 times its initial cell density to 106 cells/mL under all dilution conditions. This revealed that the nutrient composition of tomato juice is suitable for Euglena growth.

“During static incubation, tomato juice diluted with water separated into a layer of solid sediment and an upper layer of aqueous solution in the container, and Euglena proliferated actively near the boundary of these layers. Therefore, when cultivated under aerobic conditions using ‘tomato medium (filtered),’ in which the solid components of tomato juice were removed, Euglena was distributed throughout the cultivation medium,” notes Dr. Yamashita.

Notably, the cell density was higher than that of the unfiltered tomato juice medium. This indicates that the removal of solid components can mitigate the effects of density, including growth space, light and nutrient acquisition, and waste accumulation.

Brand Variations in Tomato Juice Cultivation

The study expanded its analysis to four different brands of tomato juice, all of which demonstrated the ability to promote the growth of Euglena gracilis. This versatility underscores the adaptability of the proposed technology across various product lines, opening doors to widespread adoption in diverse agricultural environments.

Independent Growth of Vitamins

An intriguing revelation from the research was the observed growth of Euglena gracilis to a remarkable cell density 100 times higher than the initial cell density in a medium containing only tomato juice, even in the absence of essential vitamins.

This resilience demonstrates the robustness of the proposed cultivation method, eliminating the need for costly vitamin supplements.

Sustainability Focus

In the context of global food scarcity and malnutrition, the study aligns with the United Nations Sustainable Development Goal 2: “End hunger, achieve food security and improved nutrition, and promote sustainable agriculture.”

The proposed method not only addresses the nutritional aspect but also eliminates costs associated with conventional production processes, such as stirring, harvesting, drying, and food processing.

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Conclusion

In conclusion, the integration of everyday beverages into the cultivation of Euglena gracilis represents an innovative leap toward sustainable and cost-effective food production. The implications extend beyond scientific innovation and offer tangible solutions to urgent global issues.

“Euglena is rich in nutrients and functional ingredients, making it possible to easily fortify foods by converting some of the nutrients from foods into Euglena. Being simple and economically viable, we hope this method proves useful for sustainable, carbon-neutral foods. It could also contribute to achieving sustainable development goals related to food and hunger and has the potential to serve as a food production technology in space exploration,” concludes Dr. Yamashita, expressing hopes for the future development of this research.

As we move forward, this research paves the way for a future where accessible and affordable nutrition contributes to a more sustainable world with food security.

Contact
Kyohei Yamashita
Department of Physics, Faculty of Science, Tokyo University of Science
1-3 Kagurazaka, Shinjuku-ku
Tokyo 162-8601, Japan
E-mail: yamashita.k@rs.tus.ac.jp

Reference (open access)
Kyohei Yamashita et al, Method for growing edible Euglena gracilis in an inexpensive medium with tomato juice to a high cell density equivalent to the density in KH medium, Sustainable Food Technology (2023). DOI: 10.1039/D3FB00086A

Note: Prepared with information from the press release of the Tokyo University of Science (TUS) and the scientific article.

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