Single Cell Protein (SCP) and Mycoprotein
The dried cells of microorganisms (algae, bacteria, actinomycetes and fungi) used as food or feed are collectively known as 'microbial protein'. Since the ancient times a number of microorganisms have been used as a part of diet. Fermented yeast (Saccharomyces sp.) was recovered as a leavening agent for bread as early as 2500 B.C. (Frey, 1930). Fermented milk and cheese produced by lactic acid bacteria (Lactobacillus and Streptococcus) was used by Egyptians and Greeks during 50-100 B.C. e.g. Lactobacillus and Streptococcus. Cultured dairy products contain 107 to 1010 lactic acid bacteria per gram of product (Pederson, 1971). During the first century B.C. the palatability of edible mushrooms was also realized in Rome. In- 16th Century blue-green algae (e.g. Spirulina) was consumed as a major source of protein (Clement, 1968).
The term 'microbial protein' was replaced by a new term "single cell protein" (SCP) during the First International Conference on microbial protein held in 1967 at the Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts, U.S.A. (Scrimshaw, 1968). Criteria for coining this term was the single celled habit of microorganisms used as food and feed.
In 1973, when Second International Conference was convened at MIT, some actinomycetes and filamentous fungi were reported to produce protein from various substrates (Tannenbaum and Wangt, 1975). Since then many filamentous fungi have been reported to produce protein. Therefore, the term SCP is not logical, if an organism produces filaments.
Since the 1920s, filamentous fungi have been used for the production of protein (Thatcher, 1954). For such fungi, the term 'fungal protein' has been used by many workers. Recently, the term 'mycoprotein' has been introduced by Ranks Hovis McDougall (RHM) in the United Kingdom for protein produced on glucose or starch substrates.
Importance of mass production of microorganisms as a direct source of microbial protein was realized during World War I in Germany and consequently, baker's yeast (S. cerevisiae) was produced in an aerated molasses medium supplemented with ammonium salts. During World War II (1939-1945) the aerobic yeasts (e.g. Candida utilis) were produced for food and feed in Germany. Since World War II, considerable effort has been made to develop technologies for mass cultivation of SCP by formulating different types of growth media and improved culture of microorganisms. In the late 1950s, British Petroleum started producing the SCP from hydrocarbons since the crude oil contains 10-25 percent n-alkanes (paraffins) and established a first large scale plant in Sardinia at the end of 1975. It had a capacity of 1,00,000 tonnes SCP per annum. Large scale production has been envisaged in England and Rumania with the annual production of 60,000 tonnes bacterial mass in England. The erstwhile U.S.S.R. was the World's largest producer of SCP in 1980. The production was estimated to 1.1 million tonnes of SCP per annum (Carter, 1981).
In India, little attention has been paid on the production of SCP, though mushroom cultivation started in the early 1950s. However, work on mushroom culture at Solan (Himachal Pradesh) from 1970 onward has brought satisfactory results. Recently, National Botanical Research Institute (NBRI), Lucknow and Central Food Technological Research Institute (CFTRI), Mysore, have established Centres for mass production of SCP from cyanobacteria. At the NBRI, SCP is produced on sewage which is further utilized as animal feed (Anonymous, 1980).
Therefore, in the light of protein shortage, microorganisms offer many possibilities for protein production. They can be used to replace totally or partially the valuable amount of conventional vegetable and animal protein feed. For this, development of technologies to utilize the waste products would play a major role for the production of SCP (Roth, 1982).