Introduction of Single Cell Protein

The term Single Cell Protein (SCP) refers to the dried microbial cells or total protein extracted from pure microbial cell culture (Algae, bacteria, filamentous fungi, yeasts), which can be used as food supplement to humans (Food Grade) or animals (Feed grade). Most of the developing countries of the world are facing a major problem of malnutrition. Due to rapid growth in the population deficiency of protein and nutrients are seen in human food and as well as animal feed.  Single cell proteins have application in animal nutrition as: fattening calves, poultry, pigs and fish breading. In food it is used as : aroma carriers, vitamin carrier, emulsifying aids and to improve the nutritive value of baked products, in soups, in ready-to-serve-meals, in diet recipes and in the technical field in : paper processing, leather processing and as foam stabilizers.
 

It has been estimated that if necessary measures are not taken the malnutrition condition will lead to some major crisis in the developing countries. Therefore it is very important to increase protein production and also its availability to the population by utilizing all the available ways and also methods. The increased world demand for food and in particular feed protein spurred the search for non-conventional protein sources to supplement the available protein source. SCP production technologies arose as a promising way to solve the problem of worldwide protein shortage

Synthetic meat derived from fungus, Fusarium venenatum

Interest in microbial protein for animal fodder largely depends on production costs in relation to the prevailing price of the main market competitors, particularly soya protein and fishmeal. The reason that more microbial protein is not currently produced for fodder is due to the present low price of these conventional protein sources. However, this may change, as there have been forecasts of future shortages of soya and fishmeal.

Dietary supplement derived from algae

Production of Single Cell Protein

The production of Single Cell Protein can be done by using waste materials as the substrate, specifically agricultural wastes such as wood shavings, sawdust, corn cobs, and many others. Examples of other waste material substrates are food processing wastes, residues from alcohol production, hydrocarbons, or human and animal excreta.

The process of SCP production from any microorganism or substrate would have the following basic steps:

1. Provision of a carbon source; it may need physical and/or chemical pretreatments.

   

   Large scale biomass fermenter

2. Addition, to the carbon source, of sources of nitrogen, phosphorus and other nutrients needed to support optimal growth of the selected microorganism.
3. Prevention of contamination by maintaining sterile or hygienic conditions. The medium components may be heated or sterilized by filtration and fermentation equipments may be sterilized.
4. The selected microorganism is inoculated in a pure state.
5. SCP processes are highly aerobic (except those using algae). Therefore, adequate aeration must be provided. In addition, cooling is necessary as considerable heat is generated.
6. The microbial biomass is recovered from the medium.
7. Processing of the biomass for enhancing its usefulness and/or storability.
   
   

Advantages and Disadvantages of Single Cell Protein

Dry mass of yeast may contain 55% protein

Large scale SCP production has some advantages over the conventional food production, these advantages are :

1. Microorganisms have a high rate of multiplication to hence rapid succession of generation (algae: 2-6hours, yeast: 1-3 hours, bacteria: 0.5-2 hours)
2. They can be easily genetically modified for varying the amino acid composition.
3. A very high protein content 43-85 % in the dry mass.
4. They can utilize a broad spectrum of raw materials as carbon sources, which include even waste products. Thus they help in the removal of pollutants also.
5. Strains with high yield and good composition can be selected or produce relatively easily.
6. Microbial biomass production occurs in continuous cultures and the quality is consistent since the growth is independent of seasonal and climatic variations.
7. Land requirements is low and is ecologically beneficial.
8. It is not dependent on climate

Despite of the interesting benefits, there are some problems regarding the Single Cell Protein. As mentioned before, the main problem of SCP production is that this product may cost more than conventional food product. There are also some technical problems, such as:

Single Cell Protein - Yeast

Yeast is another source of Single Cell Protein, and have been produced since a long time ago. In World War I, Torula yeast (Candida utilis) was produced in Germany and used in soups and sausages. Nowadays, the pet food industry is a major outlet of microbial biomass. The dog, cat. fish feed is supplemented with yeasts, it will make the product more palatable to the animals. Use of yeast as food seasoning is commonly found in vegetarians diet, Torula yeast has been commercially used for this purpose, an example of this product is Hickory Smoked Dried Torula Yeast. Yeast has some advantages among other SCP sources, such as:

Food seasoning made from Torula yeast

1. Easy to harvest because of their size (larger than bacteria)
2. High level of malic acid content
3. High lysine content
4. Can grow at acidic pH
5. Long history of traditional use
   
   

This nutritious microbe unfortunately has few disadvantages that have to be taken as consideration, such as:

1. Lower growth rates compared to bacteria
2. Lower protein content than bacteria (45-65%)
3. Lower methionine content than bacteria, solved by the addition of methionine in the final product.

Single Cell Protein - Algae

Spirulina

Since a decade ago studies on Single Cell Protein (SCP) had drawn the attention of scientist to bridge the protein gap. The use of algae as food and feed is known since centuries as they form part of the diets is East Asian countries as well as the natives in Central Africa. Some of the algae like Chloralla, Soenedesmus, Coelastrum and Spirulina have been found to suitable for mass cultivation and utilization. The advantages in using algae include simple cultivation, effective utilization of solar energy, faster growth and high protein and nutrient content.

Cultivation of Spirulina

 

In tropical countries Spirulina  cultured under authotrophic, heterotrphic and mixotrophic conditions. 

• Mass cultivation easier than other algal cultivation because aeration of CO₂ is not necessary for this species since it can maximally utilizes the amounts of carbon

Single Cell Protein - Filamentous Fungi

Filamentous Fungi

Background

In 1973, when Second International Conference was convened at MIT, some actinomycetes and filamentous fungi were reported to produce protein from various substrates. Since then many filamentous fungi have been reported to produce protein. Therefore, the term SCP is not logical, if an organism produces filaments. The term 'mycoprotein' has been introduced by Ranks Hovis McDougall (RHM) in the United Kingdom for protein produced on glucose or starch substrates. 3000 fungal isolates "from all over the world" were tested for efficiency of growth, and safety as food.

 Production of Fungal Biomass, the Mycoprotein (other than Mushrooms)

During the World War II, attempts were made to use the cultures of Fusarium and Rhizopus grown in fermentation as protein food. The inoculum of Aspergillus oryzae or Rhizopus arrhizus is chosen because of their non-toxic nature. Saprophytic fungi grow on complex organic compounds and render them into simple forms. As a result of growth, high amount of fungal biomass is produced. Mycelial yield vary widely depending upon organisms and substrates. Strains of some species of moulds, for example, Aspergillus niger, A. fumigatus, Fusarium graminearum are very hazardous to human, therefore, use of such fungi should be avoided or toxicological evaluations should be done before recommending to use as SCP. Substrates used for single cell protein production in filamentous fungus are given in Table 1. 

Table 1: Microorganism and substrate used for single cell protein production

Microorganism	Substrate
Fungi
Aspergillus fumigatus	Maltose, Glucose
Aspergillus niger, A. oryzae, Cephalosporium eichhorniae, Chaetomium cellulolyticum	Cellulose, Hemicellulose
Penicillium cyclopium	Glucose, Lactose, Galactose
Rhizopus chinensis	Glucose, Maltose
Scytalidium aciduphilium, Thricoderma viridae, Thricoderma alba	Cellulose, Pentose
Paecilomyces varioti	Sulphite waste liquor
Fusarium graminearum	Starch, Glucose

Bhalla et al. (2007)

Single Cell Protein - Bacteria

Many species of bacteria have been investigated for use in single cell protein production. Methylophilus Methylotrophus has a generation time of about 2 hours and is usually and mainly used in animal feed as bacteria, in general produce a more favorable protein composition than yeast or fungi. Therefore the large quantities of SCP animal feed can be produced using bacteria. Among the characteristics that make bacteria suitable for this application include:

• Their rapid growth
• Their short generation times; most can double their cell mass in 20 minutes to 2 hours.
• Capable of growing on a variety of raw materials, ranging from carbohydrates such as starch and sugars, to gaseous and liquid hydrocarbons such as methane and petroleum fractions, to petrochemicals such as methanol and ethanol.
• Suitable nitrogen sources for bacterial growth include ammonia, ammonium salts, urea, nitrates, and the organic nitrogen in wastes.
• A mineral nutrient supplement must be added to the bacterial culture medium to furnish nutrients that may not be present in natural waters in concentrations sufficient to support growth.

Comparisons of Single Cell Protein Sources

The interesting part on this topic is Anupama and Ravindra (2000) had come out with a table to compare the SCP from algae, fungi and bacteria. The parameters used by them to evaluate the ranking of SCP showing that nucleic acid from algae is safer than fungi and bacteria. Nucleic acid from fungi is much better than bacteria due to their low nucleic acid contents.  Therefore the ranking will be algae > fungi > bacteria.

The comparison chart shows the composition of SCP from the respective organisms.

Component	Percentage composition of weight
	Algae	Fungi	Bacteria
True Protein	40-60a	30-70a	50-83a
Total nitrogen (Protein + nucleic acids)	45-65a	35-50a	60-80a
Lysin	4.6-7.0a	6.5-7.8a	4.3-5.8a
Methionine	1.4-2.6a	1.5-1.8a	2.2-3.0a
Fats/Lipids	5-10a	5-13a	8-10a
Carbohydrate	9	NA	NA
Bile pigments and Chlorophyll	6	NA	NA
Nucleic acids	4-6a	9.70	15-16a
Mineral acids	7	6.6	8.6
Amino acids	NA	54	65
Ash	3	NA	NA
Moisture	6.0	4.5-6.0a	2.8
Fiber	3	NA	NA

 ^a The yield varies with the type of substrate used, the specific organism used and the culture conditions maintained. NA - Not available

Sources : Brock, 1989; Frazier and Westhoff, 1990;  Powar and Daginawala, 1995; Ziino et al., 1999

Comparison of various parameters for SCP production from algae, fungi and bacteria