Single cell protein or SCP refers to the microbial cells or total protein extracted from pure microbial cell culture, or monoculture which can be used as protein supplement for humans and animals. The word SCP is considered to be appropriate since most of the microorganism grow as single or filamentous individuals. This is in contrast to complete multi cellular plants and animals. If the single cell protein is suitable for human consumption it is considered as food grade. When it is used as animal feed supplement it is not suitable for human consumption.

Single cell protein broadly refers to the microbial biomass or protein extracts used as food or feed additive besides high protein content about 60 to 82% of dry cell weight.SCP also contains fats, carbohydrates, nucleic acids, vitamins and minerals. Another advantage with SCP is that it is rich in certain essential amino acids like lysine, methionine which are usually limiting in most plant and animal foods. Thus SCP is of high nutritional value for human or animal consumption.

It is estimated that about 25% of the world's population currently suffers from hunger and malnutrition. Most of these people live in developing countries therefore single cell protein deserve a serious consideration for its utility as a nutritional supplement. Single cell protein can also be used for the isolation of several compounds that is carbohydrates, fats, vitamins and minerals.

Advantages of Using Microorganism for Single Cell Protein Production

The protein producing capabilities of a 250 kg cow and 250 gm of a microorganism are often compared. The cow can produce about 200 gm of protein per day. On the other hand microorganisms can produce theoretically when grown under ideal conditions can produce about 22 to 25 tons of protein.

There are many advantages of using microorganism for single cell protein production as listed below.

1. Microorganisms grow at a very rapid rate under optimum culture conditions. Some microbes double their mass in less than 30 minutes.

2. The quality and quantity of protein contents in microorganisms is better compared to higher plants and animals.

3. A wide range of raw materials which are other wise wasted can be fruitfully used for single cell protein production.

4. The culture conditions and the fermentation processes are very simple.

5. Microorganisms can be easily handled and subjected to genetic manipulations.

6. Safety, acceptability and toxicology of single cell protein.

7. There are many non technological factors that influence the production of single cell protein. These include the geographical, social, political and psychological factors.

8. In many countries there are social and psychological barriers to use microorganisms as food sources. It is desirable to first consider the safety, acceptability and toxicology of single cell protein. Particularly when it is considered for human consumption.

There are several limitations for the wide spread use of single cell protein. They are as listed below.

1. Nucleic acid content of microbial biomass is very high like 4 to 6% in algae, 10 to 15% in bacteria, and 5 to 10% in yeast. This is highly hazardous since human's habit limited capacity to degrade nucleic acids.

2. The presence of carcinogenic and other toxic substance is often observed in association with single cell protein. These include the hydrocarbons, heavy metals, mycotoxins, and some contaminations.

3. The nature and production of these compounds depends on the raw materials and the type of organism used.

4. There is a possibility of contamination of pathogenic microorganisms in the single cell protein.

5. The digestion of microbial cells is rather slow. This is frequently associated with indigestion and allergic reactions in individuals.

6. Food grade production of single cell protein is more expensive than some other sources of proteins that are like soy milk or soy products. This mainly depends on the cost of raw materials in general single cell protein for human consumption is 10 times more expensive than single cell protein for animal feed.

For the above said reasons many countries give low priority for the use of single cell protein for human consumption. In fact mass production of single cell protein using costly raw materials has been discontinued in some countries like Japan, England, and Italy etc. However these countries continue their efforts to produce single cell protein form cheap raw materials such as organic wastes.

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