Single Cell Protein (SCP): Sources, and Applications

The global population is continually increasing, and there is a growing demand for protein-rich food. However, traditional livestock farming cannot fulfill the current population’s required quantity of protein-rich food. Therefore, to meet the need of the current population, an alternative protein source known as single-cell protein (SCP) was developed in the mid-20th century.

Previously, the single-cell protein was termed as ‘microbial protein.’ Later a new term ‘single cell protein’ replaced the term’ microbial protein. Further, it is called “single-cell” protein because these microorganisms are typically grown and harvested as individual cells rather than as part of a larger organism.

Sources of Single Cell Protein (SCP) Production

Microorganisms are the only source of single-cell protein. Microorganisms that have the following characteristics are selected for the production of single-cell proteins;

1. The microorganisms should be able to accumulate a substantial protein content within their cellular structures.
2. Microorganisms with a fast growth rate are preferable as they allow for more efficient and scalable production processes.
3. The selected microorganisms should be non-toxic and safe for human consumption or animal feed. 
4. Select of microorganisms that is able to survive under various environmental conditions, such as temperature, pH, and salinity.
5. The microorganisms should be capable of utilizing a wide range of substrates or feedstock for growth and protein production.
6. The microorganisms should possess genetic manipulation capabilities depending on the desired protein or compound to be produced. 
7. Microorganisms selected for SCP production should be flexible to large-scale cultivation and downstream processing.

Some of the examples of microorganisms used in the production of single-cell protein are as follows;

1. Algae: Chlorella pyrenoidosa, Scenedesmus actus, Spirulina maxima
2. Bacteria: Achromobacter delvacvate, Bacillus megaterium, Cellumonas spp, Methylomonas clara, Pseudomonas spp.
3. Actinomycetes: Nocardia spp, Thermomonospora fusca, 
4. Fungi: 

• Yeast- Candida lipolytica, C.utilis, B.utilis, Saccharomyces cerevisiae, S.fragilis, Rhodotorula glutinis, Torulopsis spp.
• Molds– Aspergillus niger, Trichoderma viride, Paecilomyces varioti.
• Mushrooms– Agaricus campestris, Morchella crassipes 

Nutritional value of Single Cell Protein

Microorganisms not only contain large quantities of protein, but they also contain carbohydrates, fats, vitamins, mineral salts, as well as non-protein nitrogenous substances (NPN) such as amino acids. Therefore, the average composition of single-cell protein, according to Al-Mudhafr et al. (2019), is given in the table below;

Production of Single Cell Protein

Production of single-cell protein completes within various steps that are as follows;

Step 1: Selection of strains: 

It is a crucial step as the quality of protein depends on the type of microbe used for production. Only the microbes that have a fast growth rate and do not harm the consumers by producing toxic effects are preferable. Further, a suitable substrate required for the growth of the selected microbe should also be chosen.

Step 2: Fermentation: 

The selected microbes are then placed in a fermenter that is equipped with an aerator, thermostat, pH meter, etc, or in the trenches or ponds. Microbes are grown in fed-batch culture.

Step 3: Harvesting: 

When the colonies of microbes are fully developed, they are then harvested. The bulk of cells are separated from fermenters by decantation.

Step 4: Post-harvest treatment: 

After harvesting, cells are subjected to post-harvest treatment that includes; separation by centrifugation, washing, drying, etc.

Step 5: Single cell protein (SCP) processing for food: 

The dried cells are further processed to remove impurities, enhance nutritional content, and enhance texture and flavor.

Applications of Single-Cell Protein

Single-cell protein has a wide range of applications in various sectors. These are as follows;

1. Protein supplement: SCP can be useful as a supplement or substitute for traditional protein-rich ingredients like meat, soy, and fish meal. SCP offers a sustainable solution to address the increasing global demand for protein, particularly in regions with scarce protein sources.
2. Health food: Single-cell protein (SCP) can be utilized in producing healthy foods due to its high nutritional value and functional properties. It can be incorporated into weight management foods like meal replacement shakes or low-calorie snacks. Similarly, it can also be used to control obesity, instant energy source, etc. 
3. In therapeutics and natural medicines: Single-cell protein (SCP) has potential applications in therapeutics and natural cures, including the production of therapeutic proteins, drug delivery systems, natural medicine production, probiotics, nutraceuticals, and antimicrobial agents. 
4. In cosmetics: Single cell protein (SCP) can also be utilized as an ingredient to produce cosmetic products. 
5. Poultry and cattle feed: Single-cell protein (SCP) can be a valuable ingredient in poultry and cattle feed. It serves as a sustainable alternative to traditional protein sources like soybean meal or fish meal. 

Advantages of Single Cell Protein (SCP)

Single-cell protein has several benefits that are as follows;

1. Single-cell proteins can be produced in a short duration due to the rapid succession generation of microorganisms.
2. The genetic content of microorganisms can be easily adaptable. As a result, diverse amino acid compositions can be produced. (Adipex)
3. The single-cell proteins are highly rich in protein content.
4. It requires the cheapest raw material as a substrate for the growth of microorganisms.
5. It can be produced at any season in a controlled environment.
6. Its production does not require a large land area and is ecologically beneficial.

Disadvantages of Single Cell Protein (SCP)

Despite having many benefits, single-cell proteins also have some disadvantages, such as;

1. In some cases, toxic secondary metabolites in single-cell proteins may be present.
2. Single-cell protein (SCP) from certain microorganisms may lack essential nutrients, such as certain amino acids or vitamins. Therefore, ensuring a well-balanced nutritional profile in single-cell protein (SCP) can be challenging.
3. Some single-cell proteins (SCP) derived from some microorganisms might have allergic effects in susceptible individuals. Therefore, it is important to thoroughly evaluate the allergenicity of single-cell proteins and consider potential risks for consumers.
4. Kidney stones or gout might develop if consumed in higher amounts.
5. It can also cause the stimulation of gastrointestinal reactions due to poor digestibility.

References

1. R.C. Dubey and S. Chand. A Text Book of Biotechnology. S.Chand & Company Pvt. Ltd. 5th edition 2014.
2. Adnan W. H. Al-Mudhafr and Abeer M. A. Al-Garawy. Microbiological Sources and Nutritional Value of Single Cell Protein (SCP). J. Nutrition and Food Processing, 2019. 2(2);Doi:10.31579/2637-8914/013.