Single Cell Protein: Definition, History, Production, Examples, Applications

Single Cell Protein (SCP) refers to the dead and dry cells of microorganisms such as yeast, bacteria, fungi, and algae. These SCPs are used as food or feed supplements and can serve as an alternative to traditional protein sources. SCPs are rich in protein and contain all essential amino acids.

SCPs have a high protein content with all essential amino acids, making them a valuable protein supplement. SCP can be used as a protein supplement for both humans and animals. Algae, fungi, yeast, and bacteria have a high protein content in their biomass, making them suitable for SCP production.

Single Cell Proteins: Definition, History, Production, Examples, Applications of SCP


Single Cell Protein Definition

  • Single-cell proteins are bacterial or fungal proteins obtained by culturing single-celled organisms.
  • Single cell protein (SCP) is referred to as a dried mass of microbes such as bacteria, yeast, fungi, and algae.

Read: Vitamin B12 Production By Fermentation

What are single cell Proteins?

  • Single-cell proteins are bacterial or fungal proteins obtained by culturing single-celled organisms
  • Single-cell proteins are also called microbial proteins and bacterial proteins. 
  • The most important single-cell proteins are yeast protein, bacterial protein, and algal protein.
  • Single-cell proteins are extremely rich in nutrients. Among them, the protein content is as high as 40% to 80%, which is 10% to 20% higher than that of soybeans, and more than 20% higher than that of meat, fish, and cheese.
  • Single-cell protein also contains a variety of vitamins, carbohydrates, lipids, minerals, rich enzymes, and biologically active substances, such as coenzyme A, coenzyme Q, glutathione, ergosterol, etc.
  • It is an important protein source in the modern feed industry and food industry.
  • Through microbial fermentation, a large number of single-cell proteins can be produced, which can not only be eaten directly by humans but also can be used as high-protein feed for livestock and poultry, providing us with high-quality and high-priced meat protein.

Single Cell Proteins History

  • During World War I, Germany replaced half of its imported protein sources with yeast. 
  • Pruteen was the first commercial single-cell protein used as an animal feed additive.
  • The term SCP was coined in 1966 by Carroll L. Wilson of MIT.
  • In 1967, at the first World Conference on Single-Cell Proteins, microbial bacterial proteins were collectively referred to as single-cell proteins.

Microorganisms used for Single Cell Protein Production

  • The cultivation of single-cell protein is made by using a special microorganism as a strain such as yeast or bacteria
  • A wide variety of microorganisms are used to produce single-cell proteins, including bacteria, actinomycetes, yeasts, molds, and certain protists. 
  • These microorganisms have characteristics such as the protein and other nutrients they produce are high in content, have no pathogenic effect on the human body, have a good taste and are easy to digest and absorb, require simple culture conditions, and grow rapidly.
  • Fungi: Aspergillus niger, Aspergillus fumigatus, Rhizopus cyclopean
  • Yeast: Saccharomyces cerevisiae, Candida utilis, Candida tropicalis
  • Algae: Spirulina (spa), Chondrus crispus, Chlorella pyrenoidosa
  • Bacteria: Lactobacillus, Pseudomonas fluorescens, Bacillus megaterium.

Read: Uses of Enzymes in Food and Beverages

Raw Materials used for Single-Cell Protein Production

  • The raw materials for the production of single-cell protein are quite extensive; for algae, only carbon dioxide and sunlight are enough, while bacteria, yeast, and mold require carbohydrates, ethanol, hydrocarbons, etc.
  • To produce single-cell protein carbon sources and energy sources are required.
  • In addition, the raw materials also include nitrogen sources (such as ammonium salts or nitrates) and inorganic elements (such as calcium, phosphorus, iron, magnesium, etc.) are also required.
  • Raw materials such as Agricultural waste, wastewater, such as straw, bagasse, sugar beet bagasse, sawdust, and other cellulose-containing wastes, and processing wastewater of agricultural and forestry products.
  • Industrial waste, wastewater, such as food, sugar-containing organic wastewater, sulfite pulp waste liquid, etc. are discharged from the fermentation industry.
  • Oil, natural gas, and related products, such as crude oil, diesel, methane, ethanol, etc.


Single Cell Protein Production

The production process of single-cell protein is also relatively simple: after the preparation and sterilization of the culture medium are completed, they and the strains are put into the fermentation tank, the fermentation conditions are controlled, and the strains will multiply rapidly; The bacterial cells are collected by other methods, and finally after drying, the finished product of single-cell protein is made.


Single Cell Protein Examples

1. Yeast protein: Yeast in fungi was used earlier in food processing, including brewing, baking, and other foods. Yeast contains more than half of its dry-weight protein but is relatively devoid of sulfur-containing amino acids. In addition, yeast contains a high amount of nucleic acid, excessive intake of yeast protein will cause the level of uric acid in the blood to increase, causing metabolic disorders in the body.

2. Bacterial protein: The production of bacterial proteins generally uses hydrocarbons (such as natural gas or asphalt) or methanol as substrates, and their protein content accounts for more than 3/4 of the dry weight, and the essential amino acid composition also lacks sulfur-containing amino acids. Fatty acids are mostly saturated fatty acids. Generally, these microbial proteins cannot be eaten directly, and impurities such as cell walls, nucleic acid, and ash need to be removed. The principle is similar to soybean processing in terms of technology. Bacterial protein isolate is obtained after bacterial protein extraction. Its chemical composition is similar to soybean protein isolate, and its nutritional value is also similar to soybean protein isolate after supplementing with sulfur-containing amino acids.

3. Algal protein: Chlorella and Spirulina are the most eye-catching, they are two kinds of microalgae that grow rapidly in seawater, and their protein content is 50% and 60% (dry weight), respectively. In addition to less, other essential amino acids are very rich.


Advantages of Single cell protein

  • It has high production efficiency, thousands of times higher than that of animals and plants, mainly because of the fast growth and reproduction rate of microorganisms.
  • There is a wide range of raw materials for SCP production.
  • The microbes used for SCP production can be easily genetically modified to vary the amino acid composition.
  • SCP helps in decreasing the number of pollutants in the environment.
  • Single Cell Protein production is independent of climatic conditions, we can produce at any season.
  • Qualitative and Quantitative SCP can produce through these microorganisms.
  • The fermentation process and culture conditions are both simple.


Disadvantages of Single Cell Protein

  • A high nucleic acid concentration might increase uric acid levels in the blood.
  • Regular consumption of single-cell protein can result in gout and kidney stones.
  • SCP can potentially produce allergic reactions


Application of Single Cell Protein

  • The unicellular protein that comes from microbial cells is used as a food or food supplement.
  • SCP use in cosmetics for maintaining healthy hair (vitamins A and B), herbal beauty products, etc.
  • Biomass can provide a great alternative to replace or reinforce some of the protein sources such as fishmeal, soy, skimmed whey, etc.
  • Microbial biomass can be used to develop many derived products such as lipids, proteins, nucleic acids, carbohydrates, vitamins, etc. 
  • SCP is an immune control nutrient in patients with hypoproteinemia, anemia, hyperglycemia, hypercholesterolemia, etc.
  • Single-cell protein is used as a source of a variety of vitamins, carbohydrates, lipids, minerals, and rich enzymes. 

Factors Affecting Single-Cell Protein Production

1. Temperature : 
  • The effect of temperature on single-cell protein production is numerous. 
  • The optimum temperature used for the production of SCP by submerged fermentation
  • Temperature can affect the growth of microorganisms. In the optimum temperature range, as the temperature increases the growth and metabolism and the rate of the fermentation reaction increase. 
  • When the temperature exceeds the optimal temperature range as the temperature rises the microbial activity is quickly inactivated and the fermentation rate is reduced. 
  • Therefore, to ensure a normal fermentation process, it is necessary to maintain the optimum temperature.
2. pH : 
  • pH can affect the activity of microorganisms, enzymes, and fermentation rate. 
  • Based on the type of substrate and media and microorganisms the pH is vary. 
  • In defined media, the initial pH of the medium is usually adjusted to 7.2-7.3, while in the case of molasses, the pH must be neutral or slightly acidic. 
  • The pH of the medium is adjusted with NaOH, H2SO4, and HCl.  
  • In addition, pH will also affect the decomposition of nutrients in the medium. Therefore, the pH of the fermentation broth should be controlled.
3. Dissolved oxygen Concentration : 
  • The supply of oxygen is a key factor for aerobic fermentation and therefore it requires oxygen. 
  • Aeration and agitation meet the oxygen demand of a fermentation process of single-cell protein.
  • Agitation is important for heat transfer, adequate mixing, and mass transfer.
  • Aeration and agitation both maintain the homogeneous environment of culture by continuous mixing. 
  • Therefore, a large amount of oxygen must be continuously added to the fermentation broth, and stirring can increase the solubility of oxygen in the fermentation broth. 
  • The concentration of dissolved oxygen increased with the increase in the speed of agitation.
4. Concentration of nutrients : 
  • The concentration of various nutrients in the fermentation broth, especially the ratio of carbon to nitrogen, inorganic salts, and vitamins, will directly affect the growth of bacteria and the production of single-cell proteins.
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