Pulsed electric fields (PEF) for the sustainable extraction of nutrients
Sofie Schröder, Claudia Siemer, Elea Technology GmbH
In today's world, the sustainable use of raw materials is of great importance. Accordingly, the demand for environmentally friendly and energy-saving processes for obtaining nutrient-rich, sustainable foods is increasing. Many valuable nutrients can be obtained from microorganisms, such as yeasts and microalgae. They offer many advantages over plants or animals, as they are able to use low-cost feedstock and waste as carbon and energy sources to produce biomass. In addition, they have a high productivity resulting from their fast growth rate. In order to obtain the nutrients contained in the cells an effective cell disruption is necessary. Numerous methods based on chemical, mechanical and thermal principles already exist, but these are often energy-intensive and can also negatively effect the quality of the target substance. Pulsed Electric Field (PEF) technology has turned out to be a promising energy-saving alternative. The use of PEF has already been proven in several food products (e.g., chips or French fries) and is accordingly considered an established process in the industry. PEF is a process based on the application of electric fields in the form of very short pulses of high voltage in the kV range. The phenomenon that occurs is called electroporation (Figure 1). Living cells are surrounded by a membrane that protects them from their environment. The main component of the membrane are phospholipids, which in their role as non-conductors are essential components in the build-up of the natural charge, the so-called transmembrane potential. By applying an external voltage, this potential can be increased and electrocompression can be induced. If the applied voltage exceeds a critical value, the electrical pulses induce pores in the cell membrane, resulting in increased permeability. Through the pores, valuable cellular components such as proteins, lipids, nucleotides, and other ingredients can be extracted from the cells without destroying the structure of these nutrients.
PEF treatment of yeast and algae
One example of the application of PEF for the extraction of valuable components is yeast. These microorganisms are widely used in the food industry, for example, in beer and wine production. In addition, they are also utilized in the production of yeast extracts, which are found in a wide variety of products from different industries. By using PEF, valuable ingredients such as flavour enhancers, proteins or minerals can be efficiently and gently extracted from yeast cells.
The potential of PEF for the extraction of valuable components is also evident in the field of microalgae. They are considered a promising and sustainable source of bioactive compounds, proteins and pigments used in the food and health industries. PEF allows the extraction of proteins and the blue dye phycocyanin from the cells. In addition, PEF enables selective extraction of phycocyanin, resulting in higher purity compared to the use of, for example, ultrasound. This in turn results in an increase in dye quality, eliminating the need for additional purification steps.
Further fields of application for PEF as a cell disruption method
PEF not only offers the possibility of gentle extraction of valuable components from yeasts and microalgae, but also in other fields of application. For example, PEF has been shown to selectively extract recombinant protein from bacterial cells (E. coli). Compared to high-pressure homogenization, PEF treatment results in 40% less host cell protein loading, 96% less DNA loading, and 43% less endotoxin loading.[1] Further, studies showed not only a selective extraction of recombinant protein from E. coli, but also an increased yield of protein. In this context, the maximum amount of protein can be obtained at large electric field strengths and longer pulse times. In addition, it was shown that subsequent incubation of the cells at low temperatures after treatment with PEF leads to further increasing yields.[2]
PEF thus represents a promising alternative for the efficient and gentle cell disruption of yeasts, microalgae, and other microorganisms. Since PEF is already established in other areas of food production, appropriate industrial facilities are available (Figure 2). This means that the industrial application of PEF for cell disruption can be realized. Future research could help to exploit the full potential of PEF and further advance the sustainable recovery of valuable ingredients.
[1] Schottroff, F., Kastenhofer, J., Spadiut, O., Jaeger, H., & Wurm, D. J. (2021). Selective release of recombinant periplasmic protein from E. coli using continuous pulsed electric field treatment. Frontiers in Bioengineering and Biotechnology, 8, 586833.
[2] Martínez, J. M., Delso, C., Álvarez, I., & Raso, J. (2020). Pulsed electric field-assisted extraction of valuable compounds from microorganisms. Comprehensive Reviews in Food Science and Food Safety, 19(2), 530–552. https://doi.org/https://doi.org/10.1111/1541-4337.12512
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