Single-cell protein

Single-cell proteins (SCP) or microbial proteins

With the world population reaching 9 billion by 2050, there is strong evidence that agriculture will not be able to meet demand^[6] and that there is serious risk of food shortage.^[7][8] Autotrophic SCP represents options of fail-safe mass food-production which can produce food reliably even under harsh climate conditions.^[5]

History

In 1781, processes for preparing highly concentrated forms of yeast were established. Research on Single Cell Protein Technology started a century ago when

The "food from oil" idea became quite popular by the 1970s, with Champagnat being awarded the UNESCO Science Prize in 1976,^[12] and paraffin-fed yeast facilities being built in a number of countries. The primary use of the product was as poultry and cattle feed.^[13]

The Soviets were particularly enthusiastic, opening large "BVK" (belkovo-vitaminny kontsentrat, i.e., "protein-vitamin concentrate") plants next to their oil refineries in Kstovo (1973)^[14][15][16] and Kirishi (1974).^[17] The Soviet Ministry of Microbiological Industry had eight plants of this kind by 1989. However, due to concerns of toxicity of alkanes in SCP and pressured by the environmentalist movements, the government decided to close them down, or convert to some other microbiological processes.^[17]

Another type of single cell protein-based meat analogue (which does not use fungi however but rather bacteria[18]) is Calysta. Other producers are Unibio (Denmark) Circe Biotechnologie (Austria) and String Bio (India).

SCP has been argued to be a source of alternative or resilient food.^[19][20]

Production process

Single-cell proteins develop when

• Yeast
  • Saccharomyces cerevisiae
  • Pichia pastoris
  • Candida utilis
  • Torulopsis corallina
  • Geotrichum candidum
• Fungi (Mycoprotein)
  • Aspergillus oryzae
  • Fusarium venenatum
  • Sclerotium rolfsii
  • Polyporus
  • Trichoderma
  • Scytalidium acidophilum^[25]
• Bacteria
  • Rhodobacter capsulatus ^[21]
  • Methylophilus methylotrophus
  • Metylococcus capsulatus
• Algae
  • Spirulina (dietary supplement)
  • Chlorella^[26]

Properties

Large-scale production of microbial biomass has many advantages over the traditional methods for producing proteins for food or feed.

1. Microorganisms have a much higher growth rate (algae: 2–6 hours, yeast: 1–3 hours, bacteria: 0.5–2 hours). This also allows selection for strains with high yield and good nutritional composition more quickly and easily compared to breeding.
2. Whereas large parts of crops, such as stems, leaves and roots, are not edible, single-cell microorganisms can be used entirely. Whereas parts of the edible fraction of crops are indigestible, many microorganisms are digestible at a much higher fraction.^[5]
3. Microorganisms usually have a much higher protein content of 30–70% in the dry mass than vegetables or grains.^[27] The amino acid profiles of many SCP microorganisms often have excellent nutritional quality, comparable to hen's eggs.
4. Some microorganisms can build vitamins and nutrients which eukaryotic organisms such as plants cannot produce or not produce in significant amounts, including vitamin B12.
5. Microorganisms can utilize a broad spectrum of raw materials as carbon sources including alkanes, methanol, methane, ethanol and sugars. What was considered "waste product" often can be reclaimed as nutrients and support growth of edible microorganisms.
6. Like plants, autotrophic microorganisms are capable of growing on CO₂. Some of them, such as bacteria with the Wood–Ljungdahl pathway or the reductive TCA can fix CO₂ with efficiencies ranging from 2-3 times^[28] to 10 times more efficiently than plants,^[29] when also considering the effects of photoinhibition.
7. Some bacteria, such as several homoacetogenic clostridia, are capable of performing syngas fermentation. This means they can metabolize synthesis gas, a gas mixture of CO, H₂ and CO₂ that can be made by gasification of residual intractable biowastes such as lignocellulose.
8. Some bacteria are diazotrophic, i.e. they can fix N₂ from the air and are thus independent of chemical N-fertilizer, whose production, utilization and degradation causes tremendous harm to the environment, deteriorates public health, and fosters climate change.^[30]
9. Many bacteria can utilize H₂ for energy supply, using enzymes called
   water electrolysis, in a manner of speaking, those bacteria can be "powered by electricity".^[5]
10. Microbial biomass production is independent of seasonal and climatic variations, and can easily be shielded from extreme weather events that are expected to cause crop failures with the ongoing climate-change. Light-independent microorganisms such as yeasts can continue to grow at night.
11. Cultivation of microorganisms generally has a much lower water footprint than agricultural food production. Whereas the global average blue-green water footprint (irrigation, surface, ground and rain water) of crops reaches about 1800 liters per kg crop^[2] due to evaporation, transpiration, drainage and runoff, closed bioreactors producing SCP exhibits none of these causes.
12. Cultivation of microorganisms does not require fertile soil and therefore does not compete with agriculture. Thanks to the low water requirements, SCP cultivation can even be done in dry climates with infertile soil and may provide a means of fail-safe food supply in arid countries.
13. Photosynthetic microorganisms can reach a higher solar-energy-conversion efficiency than plants, because in photobioreactors supply of water, CO₂ and a balanced light distribution can be tightly controlled.
14. Unlike agricultural products which are processed towards a desired quality, it is easier with microorganisms to direct production towards a desired quality. Instead of extracting amino acids from soy beans and throwing away half of the plant body in the process, microorganisms can be genetically modified to overproduce or even secrete a particular amino acid. However, in order to keep a good consumer acceptance, it is usually easier to obtain similar results by screening for microorganisms which already have the desired trait or train them via selective adaptation.

Although SCP shows very attractive features as a nutrient for humans, however there are some problems that deter its adoption on global basis:

• Fast growing microorganisms such as bacteria and yeast have a high concentration of
  RNases to hydrolyse RNA with release of nucleotides from cell to culture broth.^[31]
• Similar to plant cells, the cell wall of some microorganisms such as algae and yeast contains indigestible components, such as cellulose. The cells of some kind of SCP should be broken up in order to liberate the cell interior and allow complete digestion.[32]
• Some kind of SCP exhibits unpleasant color and flavors.
• Depending on the kind of SCP and the cultivation conditions, care must be taken to prevent and control contamination by other microorganisms because contaminants may produce toxins such as
  mycotoxins or cyanotoxins. An interesting approach to address this problem was proposed with the fungus Scytalidium acidophilum which grows at a pH as low as 1, outside the tolerance of most microorganisms. This allows it to grow on acid-hydrolysed paper waste at low-cost.^[25]
• Some yeast and fungal proteins are deficient in methionine.

See also

• Solein: a single cell protein made by Solar Foods Ltd. Finland-based.^[33]
• Kiverdi, Inc^[34][35] and subsidiary Air Protein^[36][37][33] by Lisa Dyson. California-based.
• Avecom - Belgium-based^[33]
• Unibio - Denmark-based^[38]
• Calysta - California-based
• Circe Biotechnologie - Austria-based^[39]
• Superbrewed Food (formerly White Dog Labs). Delaware-based^[40]
• Deep Branch - UK-based^[33]
• LanzaTech^[33]
• Purple bacteria: a type of single-cell protein^[41]
• Kyanos^[42]
• NovoNutrients^[43][44][35]
• Deep Branch Biotechnology^[35][45][46]
• Fermentative hydrogen production
• Hydrogenotrophs^[36]
• Alternative foods
• Microbial food cultures

References