Single Cell Protein (SCP): Microbes, Production, Advantages, Disadvantages & Applications

Table of Contents

• Introduction to Single Cell Protein (SCP)
• History of Single Cell Protein (SCP)
• Organisms used as Single Cell Protein (SCP) and the substrate used for their production
• Fungi and substrates utilized by them and the protein content produced
• Algae and substrates utilized by them and the protein content produced
• Bacteria and substrates utilized by them and the protein content produced
• Single Cell Protein production method
• Advantages of Single Cell Protein
• Disadvantages of Single Cell Protein
• Applications of Single Cell Protein
• References

Introduction to Single Cell Protein (SCP)

• Single Cell Protein (SCP) refers to the dried cells of microorganisms that are consumed as a protein supplement by both humans and animals.
• The protein is obtained from microbial cells such as yeast, fungi, algae, and bacteria, which are cultivated on different carbon sources to enable protein synthesis.
• Due to the continuous increase in population and the global problem of nutrient deficiency, microbial biomass has gained importance as an alternative source of food and feed.
• SCP is rich in vitamins, including thiamine, riboflavin, pyridoxine, nicotinic acid, pantothenic acid, folic acid, biotin, cyanocobalamin, ascorbic acid, β-carotene, and α-tocopherol.
• It provides essential amino acids, particularly lysine and methionine, which are vital for human and animal nutrition.
• In addition to proteins and amino acids, SCP also contains minerals, nucleic acids, and lipids, contributing to its nutritional value.
• Microorganisms selected for single-cell protein production must possess certain important characteristics to ensure safe and efficient use. These include:
• Absence of pathogenicity and toxicity, making them safe for consumption.
• High protein content and good quality of protein.
• Good digestibility and acceptable organoleptic properties (taste, texture, and smell).
• High growth rate to allow rapid biomass production.
• Ability to adapt to unusual environmental conditions such as varying pH levels, temperature ranges, and mineral concentrations.
• Capacity to utilize a wide range of carbon and nitrogen sources for growth and protein production.

History of Single Cell Protein (SCP)

• The development of Single Cell Protein (SCP) began during World War I.
• In 1919, Sak in Denmark and Hayduck in Germany introduced a method called Zulaufverfahren, where a sugar solution was continuously fed into an aerated suspension of yeast, instead of simply adding yeast to a diluted sugar solution.
• In Germany, Saccharomyces cerevisiae was produced from molasses to serve as a protein substitute.
• During the Second World War, microorganisms such as Candida arborea and Candida utilis were used for SCP production.
• Specifically, Candida utilis was included in soups and sausages as a protein source during World War II.
• After the war, many industries were established in the USA and Europe, focusing particularly on the large-scale production of C. utilis.
• During the 1960s and 1970s, SCP production industries expanded across the UK, France, Italy, Russia, Japan, and Taiwan.
• The actual term “Single Cell Protein” was coined by Carol L. Wilson in 1966.
• In the 1960s, researchers at British Petroleum (BP) developed the proteins-from-oil process, a technology for SCP production.
• Early experimental work was carried out by Alfred Champagnat at BP’s Lavera Oil Refinery in France, where a small pilot plant began operating in March 1963.
• For his pioneering contributions, Champagnat was awarded the UNESCO Science Prize in 1976.
• In the Soviet Union, large SCP plants producing BVK (belkovo-vitaminny kontsentrat or “protein-vitamin concentrate”) were set up alongside oil refineries — one in Kstovo (1973) and another in Kirishi (1974).
• By 1989, the Soviet Ministry of Microbiological Industry operated eight plants, but growing environmentalist pressure led the government to shut them down or convert them to other microbiological processes.
• At the Second International Conference held at MIT in 1973, new findings were reported on the ability of actinomycetes and filamentous fungi to produce protein using various substrates.
• In more recent times, among the European Communist countries, Russia maintained the highest SCP production capacity, with at least 86 operational plants using different substrates.

Organisms used as Single Cell Protein (SCP) and the substrate used for their production

Microalgae

• They are phototrophic organisms.
• Considered potential SCP due to their chemical composition, which includes proteins, essential fatty acids (especially omega-3), and various bioactive compounds.
• They have a relatively low nucleic acid content (3–8%).
• Advantages: simple cultivation methods, effective utilization of solar energy, rapid growth, and high protein yield.
• Disadvantages: economical limitations in scaling-up, digestibility problems due to the need for cell wall disruption, requirement of a large surface area for cultivation, and high contamination risk in open ponds.
• Examples: Tetraselmis suecica, Isochrysis galbana, Dunaliella tertiolecta, Chlorella stigmatophora, Spirulina spp.

Bacteria

• Bacteria are considered potential SCP because they possess high protein content (50–80%), along with vitamins, phospholipids, and other functional molecules.
• They can grow on a wide range of substrates, including carbohydrates, gaseous, and liquid hydrocarbons.
• Advantages: ability to use many types of substrates, short generation time, and production of vitamins and micronutrients.
• Disadvantages: issues of palatability, high nucleic acid content, and possible production of toxins.
• Examples: Methylobacterium extorquens, Methylococcus capsulatus, Rhodobacter sphaeroides, Afifella marina.

Fungi (Yeasts and Molds)

• Fungi can be divided into unicellular yeasts and molds.
• Yeasts: mainly used in aquaculture as they are protein-rich, with crude protein content of 38–52%.
• Molds: found to be highly digestible by fish.
• Advantages of Yeasts: high malic acid content, ability to grow in acidic pH, and ease of harvesting.
• Advantages of Molds: contain a relatively high nucleic acid content (up to 10%).
• Disadvantages: possible presence of toxins, slower growth rate, and lower protein content (45–65%) compared to bacteria.
• Examples:
• Yeasts: Saccharomyces cerevisiae, Kluyveromyces marxianus
• Fungi (Molds): Aspergillus oryzae, Yarrowia lipolytica

Fungi and substrates utilized by them and the protein content produced

Single Cell Protein (SCP) – Substrates, Fungi, and Protein Content

S.N.	Substrate	Fungi	Protein content
1	Maltose, Glucose	Aspergillus fumigatus
2	Cellulose, Hemicellulose	Aspergillus niger, A. oryzae, Cephalosporium eichhorniae, Chaetomium cellulolyticum
3	Glucose, Lactose, Galactose	Penicillium cyclopium
4	Hydrocarbons	Yarrowia lipolytica
5	Ethanol	Candida utilis
6	Methanol	Pichia spp., Pichia pastoris
7	Cellulose, Pentose	Scytalidium aciduphilium, Trichoderma viridae, Trichoderma alba
8	Glucose	Fusarium venenatum	44
9	Sulphite waste liquor	Paecilomyces varioti, Candida utilis
10	Starch, Glucose	Fusarium graminearum
11	Starch	Saacharomycopsis fibuligera, Candida utilis, Saccharomyces cerevisiae
12	Whey
13	Banana waste, Apple pomace, Citrus pulp, Potato starch processing waste, Waste liquor	Aspergillus niger	18, 17-20, 25.6, 38, 50
14	Orange peel	Aspergillus niger, Rhizopus oryzae, Saccharomyces cerevisiae
15	Banana peel	Aspergillus terreus
16	Bergamot fruit (citrus fruit) peel	Penicillium roqueforti, Penicillium camemberti
17	Banana peel, pineapple peel, papaya peel	Phanerochaete chrysosporium, Panus tigrinus
18	Papaya waste, cucumber peelings, pomegranate rind, pineapple skin, watermelon skin	Rhizopus oligosporus
19	Orange peel	Trichoderma viride, Trichoderma reesei
20	Orange pulp, brewer’s spent grain, potato & carrot skins, cucumber & orange peels, discarded foods	S. cerevisiae	38.5, 49.3, 53.4, 39

Algae and substrates utilized by them and the protein content produced

Single Cell Protein (SCP) – Substrates, Algae, and Protein Content

S.N.	Substrate	Algae	Protein content
1		Anabaena cylindrica	43-56
2		Aphanizomenon flosaquae	62
3		Arthrospira maxima	56-77
4		Chlorella ellipsoidea	42.2
5		Chlorella ovalis	10.97
6		Chlorella pyrenoidosa	57
7		Chlorella spaerckii	6.87
8		Chlorella vulgaris	51-58
9		Dunaliella primolecta	12.26
10		Dunaliella salina	57
11		Dunaliella tertiolecta	11.4
12		Porphyridium aerugeneum	31.6
13		Porphyridium cruentum	28-39
14		Scenedesmus almeriensis	41.8
15		Scenedesmus obliquus	50-55
16		Spirulina platensis	60-71
17		Tetraselmis	36
18		Tetraselmis chuii	31-46.5
19	Soda ash effluent	Chaetomorpha antennina, Ulva fasciata, Chlorella	14-18.2, 13.7-18.6
20	Tofu waste, Tempeh waste, Cheese waste	Chlorella spp.	52.32, 52, 15.43
21	Saline sewage effluents	Chlorella salina	51
22	Natural habitat	Gracilaria domingensis, Gracilaria birdiae, Laurencia filiformis, Laurencia intricate, Chondrus crispus, Porphyra umbilicalis, Gracilaria verrucosa	6.2, 7.1, 18.3, 4.6, 20.1, 15-37, 7-23
23	Wastewater	Chlorella sorokiniana, Scenedesmus obliquus	45, 52
24	Salinated water, Desalinated water	Spirulina	48.59, 56.17
25	CO2 and sunlight	Chlorella pyrenoidosa, Scenedesmus quadricauda, Spirulina maxima	53
26	n-Alkanes, kerosene	Candida intermedia, C. lipolytica, C. tropicalis, Nocardia spp.
27		Nannochloropsis spp.	39.3
28		Nannochloropsis gaditana	39.3
29		Desmodesmus spp.	37.3
30		Schizochytrium spp.	9.4-42.5
31		Chlorella vulgaris	17.9
32		Scenedesmus spp.	48

Bacteria and substrates utilized by them and the protein content produced

S.N.	Substrate	Bacteria	Protein content
1	Orange wastes, lemon wastes	Rhodococcus opacus
2	Commercial shrimp feed	Afifella marina STW181	>46
3	Ram horn	Bacillus cereus Bacillus subtilis Escherichia coli	68 71 66
4	Potato starch processing waste	Bacillus licheniformis Bacillus pumilis	38 46
5	Soybean hull	Bacillus subtilis spp	26

Single Cell Protein production method

1. Selection of Substrate and Strain

• Fast-growing microorganisms rich in protein are selected.
• Strains must possess suitable growth characteristics such as safety, digestibility, and ability to use low-cost substrates.
• Suitable substrates (agro-wastes, industrial by-products, or other low-cost carbon sources) are chosen to support microbial growth.

2. Fermentation

• The process is carried out in a fermenter, designed for the mass culture of microbial cells.
• Microorganisms are inoculated into the medium and allowed to multiply.
• Key conditions such as temperature, pH, aeration, and oxygen supply are carefully controlled to maximize biomass yield and protein content.

3. Harvesting

• After fermentation, microbial cells are separated from the growth medium.
• Techniques include centrifugation, filtration, or flocculation.
• A major challenge is the efficient harvesting and purification of biomass, which impacts cost-effectiveness.

4. Post-harvest Treatment

• Harvested cells are dried to preserve them, reduce bulk, and improve storage stability.
• Drying methods may include spray-drying, drum-drying, or freeze-drying.

5. SCP Processing for Food Use

• Dried microbial biomass undergoes further processing:
• Removal of undesirable compounds (e.g., nucleic acids, toxins).
• Enhancement of nutritional quality (protein digestibility, vitamin enrichment).
• Improvement of sensory properties (flavor, texture, and color).
• Final products can be incorporated into animal feed or human food formulations.

6. Integration with Circular Economy

• Optimal SCP production emphasizes sustainable resource use.
• Low-cost agro-industrial wastes, methane, or wastewater can be used as substrates.
• This approach reduces environmental impact and supports a circular economy model by turning waste into high-value protein.

Advantages of Single Cell Protein

• Microorganisms grow much faster than protein-rich crops, which may take up to a year to produce.
• SCP provides high-quality protein with a content ranging between 60–80%.
• A wide variety of low-cost raw materials can be utilized as substrates.
• The overall production process is simple and efficient.
• Microorganisms can be genetically modified to enhance yield, nutritional value, or other traits.
• Production is not seasonal, allowing continuous availability throughout the year.
• Microbes can grow on a diverse range of substrates, including waste materials.
• SCP production is eco-friendly, cost-effective, and energy-efficient, making it a sustainable protein source.

Disadvantages of Single Cell Protein

• The production process is complex, requiring precise control of environmental factors such as temperature, pH, and aeration.
• Quality maintenance is difficult, as harvesting and purification after fermentation remain challenging.
• SCP does not provide a complete profile of essential amino acids, so it is usually consumed as a supplement rather than a primary protein source.
• Consumer acceptance is limited, as many people are hesitant to consume protein derived from microorganisms.

Applications of Single Cell Protein

• Animal Feed & Nutrition: Used in poultry, pig, calf, and cattle feed to promote growth, fattening, and overall nutrition.
• Food Industry: Applied as food additives (vitamin carriers, aroma enhancers, and emulsifying agents), to improve the nutritional value of baked goods, soups, and ready-to-eat meals. SCP is also used in starter cultures for baker’s yeast, brewing, and winemaking.
• Industrial Uses: Employed as a foam-stabilizing agent and in processes like paper and leather manufacturing.
• Human Nutrition & Health: Serves as an excellent protein supplement, especially for undernourished children, as it is rich in vitamins, amino acids, and minerals.
• Medical Applications: Incorporated in therapeutic and natural medicine to help manage obesity, diabetes (by lowering blood sugar), cholesterol, stress, and to prevent fat accumulation.
• Cosmetics: Used in beauty and personal care products, such as herbal creams, lipsticks, and hair care formulations, due to its nourishing properties.

References

• Abdullahi, N., Dandago, M. A., & Yunusa, A. K. (2021). A review on the production of single-cell protein from food waste. Turkish Journal of Agriculture – Food Science and Technology, 9(6), 968–974. https://doi.org/10.24925/TURJAF.V9I6.968-974.3758
• Ali, S., Mushtaq, J., Nazir, F., & Sarfraz, H. (2017). Production and processing of single cell protein (SCP) – A review. European Journal of Pharmaceutical and Medical Research. Retrieved January 26, 2023, from www.ejpmr.com
• Barka, A., & Blecker, C. (2016). Microalgae as a potential source of single-cell proteins: A review. Biotechnology, Agronomy, and Society and Environment, 20(3), 427–436. https://doi.org/10.25518/1780-4507.13132
• Bratosin, B. C., Darjan, S., & Vodnar, D. C. (2021). Single cell protein as a potential substitute in human and animal nutrition. Sustainability, 13(16), 9284. https://doi.org/10.3390/SU13169284
• Gao, Y., Li, D., & Liu, Y. (2012). Utilization of soy molasses for single-cell protein production by Candida tropicalis. Annals of Microbiology, 62(3), 1165–1172. https://doi.org/10.1007/s13213-011-0356-9
• García-Garibay, M., Gómez-Ruiz, L., & Cruz-Guerrero, A. (2003). Yeasts and bacteria. In Encyclopedia of Food Sciences and Nutrition (pp. 5277–5284).
• Kwatra, B., Yadav, P., Balasubramaniam, S., Garg, S., & Koyande, T. (2021). A review of major microbes as single cell protein. International Journal of Medical and Biomedical Studies, 5(3). https://doi.org/10.32553/ijmbs.v5i3.1842
• Nyyssölä, A., Suhonen, A., Ritala, A., & Oksman-Caldentey, K. M. (2022). The role of single-cell protein in cellular agriculture. Current Opinion in Biotechnology, 75, 102686. https://doi.org/10.1016/J.COPBIO.2022.102686
• Pereira, A. G., Fraga-Corral, M., Garcia-Oliveira, P., Otero, P., Soria-Lopez, A., Cassani, L., Cao, H., Xiao, J., Prieto, M. A., & Simal-Gandara, J. (2022). Single-cell proteins from circular economy approaches as feed ingredients in aquaculture. Foods, 11(18), 2831. https://doi.org/10.3390/foods11182831
• Putri, D., Ulhidayati, A., Musthofa, I. A., & Wardani, A. K. (2018). Production of single-cell protein from Chlorella sp. using food processing waste as a medium. IOP Conference Series: Earth and Environmental Science, 131(1), 012052. https://doi.org/10.1088/1755-1315/131/1/012052
• Ritala, A., Häkkinen, S. T., Toivari, M., & Wiebe, M. G. (2017). Single cell protein – State-of-the-art, industrial landscape, and patents from 2001–2016. Frontiers in Microbiology, 8, 2009. https://doi.org/10.3389/FMICB.2017.02009
• Sharif, M., Zafar, M. H., Aqib, A. I., Saeed, M., Farag, M. R., & Alagawany, M. (2021). Single cell protein: Sources, production mechanisms, nutritional value, and applications in aquaculture nutrition. Aquaculture, 531, 735885. https://doi.org/10.1016/j.aquaculture.2020.735885
• Simões, A. C. P., Fernandes, R. P., Barreto, M. S., Marques da Costa, G. B., de Godoy, M. G., Freire, D. M. G., & Pereira, N. (2022). Cultivation of Methylobacterium organophilum in methanol for simultaneous SCP and metabolite production. Food Technology and Biotechnology, 60(3), 338–349. https://doi.org/10.17113/ftb.60.03.22.7372
• Srividya, A. R., Vishnuvarthan, V. J., Murugappan, M., & Dahake, G. (2013). A review on single-cell protein. International Journal for Pharmaceutical Research Scholars.
• Suman, G., Nupur, M., Anuradha, S., & Pradeep, B. (2015). Single-cell protein production: A review. International Journal of Current Microbiology and Applied Sciences, 4(9), 251–262. http://www.ijcmas.com
• Thiviya, P., Gamage, A., Kapilan, R., Merah, O., & Madhujith, T. (2022). Production of single-cell protein from different fruit wastes: A review. Separations, 9(7), 178. https://doi.org/10.3390/separations9070178
• Vasey, R. B., & Powellf, K. A. (1984). Single-cell protein. Biotechnology and Genetic Engineering Reviews, 2(1), 285–311. https://doi.org/10.1080/02648725.1984.10647802