Question

what is single cell protein and its importance and types

Answer 1

Single-cell proteins are the dried cells of microorganism, which are used as protein supplement in human foods or animal feeds. Microorganisms like algae, fungi, yeast and bacteria, utilize inexpensive feedstock and wastes as sources of carbon and energy for growth to produce biomass, protein concentrate or amino acids. Since protein accounts for the quantitatively important part of the microbial cells, these microorganisms, also called single cell protein as natural protein concentrate. With increase in population and worldwide protein shortage the use of microbial biomass as food and feed is more highlighted. Although single cell protein has high nutritive value due to higher protein, vitamin, essential amino acids and lipid content, there is a doubt to be replaced to the conventional protein sources due to their high nucleic acid content and slower in digestibility. They also may be considered as foreign material by body, which may subsequently results in allergic reactions.
Yeasts have advantages such as their larger size (easier to harvest), lower nucleic add content, high lysine content and ability to grow at acidic pH. However, the most important advantage is familiarity and acceptability because of the long history of its use in traditional fermentations. Disadvantages include lower growth rates, lower protein content (45 to 65%) and lower methionine content than in bacteria. Filamentous fungi have advantages in ease of harvesting, but have their limitations in lower growth rates, lower protein content and acceptability. Algae have disadvantages of having cellulosic cell walls which are not digested by human beings. Secondly, they also concentrate heavy metals. In the case of algae it has to be stressed that, due to technical and economical reasons, it is not the general intention to isolate and utilize the sole protein, but to propagate the whole algal biomass. So, the term SCP is not quite correct, because the micro-algal material is definitely more than just protein. To date, world-wide various sophisticated technologies are employed for mass production and processing of photoautotrophic microalgae. 
Microbes employed include:

Yeast

Saccharomyces cerevisiae

Pichia pastoris

Candida utilis

Torulopsis

Geotrichum candidum

Fungi (Mycoprotein)

Aspergillus oryzae

Fusarium venenatum

Sclerotium rolfsii

Polyporus

Trichoderma

Scytalidium acidophilum

Bacteria

Rhodobacter capsulatus 

Algae

spirulina (dietary supplement)

Chlorella



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