In this article we will discuss about:- 1. Introduction to Single Cell Protein (SCP) Production 2. Substrates Used for SCP Production 3. Microorganisms 4. Advantages 5. Challenges.
- Introduction to Single Cell Protein (SCP) Production
- Substrates Used for SCP Production
- Microorganisms Used for SCP Production
- Advantages of Using Microbes for SCP Production
- Challenges in SCP Production
1. Introduction to Single Cell Protein (SCP) Production:
A major challenge to creating a sustainable future for the world’s populations will be to secure adequate food supplies for the majority. The number of humans in the world now approximates six billion and increasing and could be over nine billion within the next 25 years. Conventional agriculture may not be able to provide sufficient supply of food especially protein.
Today new agricultural practices are widespread: high-protein cereals have been developed; the cultivation of soyabeans and groundnuts is ever-expanding; protein may be extracted from liquid wastes by ultrafiltration; and now the use of microbes as protein producers has gained wide experimental and commercial success.
This field of study has known as single-cell protein production (SCP) referring that most microorganisms used as protein producers grow as single or filamentous individuals rather than as complex multicellular organisms such as plants or animals, (microorganisms can be directly used as a food sources or as the supplements of other foods are called as single cell protein).
Single cell protein basically comprises proteins, fats carbohydrates, ash ingredients, water and other elements such as phosphorus and potassium. Eating microbes may seem strange, but people have long recognized the nutritional value of some large microorganisms, such as mushrooms.
Similarly the growth of more simple microorganisms, namely bacteria, yeast, filamentous fungi and algae can be used as the production of proteins. The quality and quantity of the protein are the major goals of SCP production. However, the microbes also contain carbohydrates, fats, vitamins and minerals and produce them from low-quality waste materials.
SCP may be used as a protein supplement for humans and animals. With human it has been considered as a protein supplement, as a food additive to improve flavor and fat binding and more recently as a replacement for animal protein in the diet.
Because humans have a limited capacity to degrade nucleic acids, additional processing is required before SCP can be used in human foods, i.e., microorganisms have high DNA/RNA contents and human metabolism of nucleic acids yields excessive amounts of uric acid, causing kidney stones and gout.
In animal feeding it can serve as a replacement for the traditional protein supplements such as fishmeal and soy meal. The high protein levels, bland odour and taste of SCP, together with ease of storage, confer considerable potential to SCP in food and food outlets. Its high protein content makes its use attractive in aquaculture, e.g., farming shrimps, prawns, trout and salmon.
The most important substrates used for the industrial production of SCP are:
(i) Molasses from sugar manufacture or hydrolysis of starch.
(ii) Spent sulfite liquor, it is a waste product of the sulphite pulping process in paper industry.
(iii) Acid hydrolysate from wood processing industries.
(iv) Agricultural waste- whey from dairy industry, fruit juice or citrus peel hydrolysate, hydrolysed starchy foods, etc.
(v) Methane, methanol and ethanol.
(vi) Paraffin, gas oil and other alkanes.
The microbes involved in SCP are mostly bacteria, fungi, yeasts and algae.
Bacteria are usually high in protein (50 to 80 percent) and have a rapid growth rate.
The principal disadvantages are as follows:
(i) Bacterial cells have small size and low density, which makes harvesting from the fermented medium difficult and costly.
(ii) Bacterial cells have high nucleic acid content relative to yeast and fungi. This can be detrimental to human beings, tending to increase the uric acid level in blood. This may cause uric acid poising or gout. To decrease the nucleic acid level additional processing step has to be introduced and this increases the cost.
(iii) The general public thinking is that all bacteria are harmful and produce disease. An extensive education programme is required to remove this misconception and to make the public accept bacterial protein.
The important bacteria used for the production of SCP are explained below:
It is an aerobic, motile, gram-negative bacterium which utilizes methanol. Hence, this bacterium is the suitable for the production of SCP from methanol. This bacterium can utilize methanol as a carbon source for SCP production. It has many advantages over n-paraffin and other alkanes, methane gas and even carbohydrates.
The merits of methanol for the production of SCP are listed below:
(i) Composition is independent of seasonal fluctuations.
(ii) There are no possible sources of toxicity in methanol.
(iii) Methanol dissolves easily in the aqueous phase in all concentrations.
(iv) No residue of carbon source remains in the harvested biomass.
ii. Pseudomonas, Cellulomonas and Alcaligenes:
These organisms can grow on wide variety of substrates, have short generation time and are high protein content.
But their use is somewhat limited by:
(i) Poor public acceptance of bacteria’s food.
(ii) Small size and difficulty of harvesting.
(iii) High content of nucleic acid.
Yeast is the most widely accepted and used organisms for SCP production. Yeasts have as advantages their larger size (easier to harvest), lower nucleic acid content, high lysine content and ability to grow at acid pH. However, the most important advantage is familiarity and acceptability because of the long history of its use in traditional fermentation.
Disadvantages include lower growth rates, lower protein content (45 to 65 percent) and lower methionine content than in bacteria. The important species of yeasts are Candida utilis, Candida lypolytica and Saccharomyces cerevisiae. These organisms can grow rapidly and utilizes pentose or hexose sugar and synthesise its accessory food for growth from simple compounds. This can be used as SCP.
3. Other Fungus:
This mould can utilize simple carbohydrates and can produce an important SCP- mycoprotein which is used for human consumption.
ii. Phanerochaete chrysosporium:
This is one of the most studied lignin degraders and is considered to have great potential Biotechnology applications and also SCP production.
The basidiomycetes or mushroom-type fungi have long been grown on lignocellulosic materials such as wood and straws and to produce edible mushrooms. The cultivation of edible mushrooms plays a prime role in the production of SCP; it is used directly as a human food.
Mushroom cultivation a technology is comprises of the following steps:
(i) Selection of suitable place and types of mushroom to be cultivated.
(ii) Design and layout of mushroom farm structure.
(iii) Techniques of compost and composting process.
(iv) Techniques and methods of spawn production and spawning.
(v) Casing and production of crops.
(vi) Environmental crop management.
(vii) Harvesting and marketing of mushrooms.
The important types of mushrooms act as human foods are Oyster mushroom (Pleurotus oystreatus), Shiitake mushroom (Lentinula edodes), Agaricus biosporus and Agaricus campestris.
Mushrooms are the most exquisite of the gastronomic treasure of the world. They have been prized as the food of gods on account of their special flavors, nutritional value and medicinal properties. Mushrooms blend well with most of the vegetables and spices to form delicious items of food.
Mushrooms are rich in proteins, vitamins and minerals, but less is carbohydrate and fats. Mushroom proteins are considered to be of high quality containing all the essential amino acids such as tryptophan and lysine, which are absent in vegetable proteins.
Mushrooms are also excellent sources of vitamin such as riboflavin, nicotinic acid, panthothanic acid, vitamin B, C, D and niacin. Mushrooms also contain minerals such as calcium, phosphorus, potassium and copper. Mushrooms are very low in sodium but good source of potassium.
Edible mushrooms are considered as a potential substitute of muscle protein on account of their digestibility, good amino acid content and about 1000 times higher production of mushroom protein per unit area. The fat content of mushroom is very low but it is rich in palmitic, steric, oleic and linoleic acid. Total carbohydrate content of mushroom is 4-5 % which consists of chitin, hemicellulose and glycogen.
Agaricus biosporius consists of pentoses, methyl pentoses, hexoses, disacchrides, amino sugars, sugar alcohols, uronides and methyl sugars. Mushroom lack starch and are low caloric food with very little fat and highly suitable for obese persons. Fibre content is very high which is helpful in excretion of waste and prevention of constipation.
Algae are another important SCP producer they can cultivate well in open ponds and need only CO2 as a carbon source and sunlight as an energy source for photosynthesis.Algae such as Chlorella and Senedesmus have long been used as food in Japan while a Spirulina maximum is widely used in Africa and Mexico.
Chlorella is used as a protein and vitamin supplement in some Japanese ice cream and breads. In some parts of the world, algae are used in ponds or lagoons to aid in the removal of organic pollution and the resultant biomass is harvested, dried and the powder added to animal feed.
(i) Microorganisms can grow at rapidly under optimum conditions; some microbes can double their mass every 0.5-1 hour.
(ii) Microorganisms are more easily modified genetically than plants and animals.
(iii) Microorganisms are more amenable to large-scale screening programme to select for higher growth rate, improved acid content, etc. and can be more easily subjected to gene transfer technology.
(iv) Microorganisms have relatively high protein content and the nutritional value of the protein is good.
(v) Microorganisms can be grown in vast numbers in relatively small continuous-fermentation processes, using relatively small land area and are also independent of climate.
(vi) Microorganisms can grow on a wide range of raw materials, in particular low-value wastes and some can also use plant- derived cellulose.
5. Challenges in SCP Production:
If SCP is to be used successfully, there are five main criteria to be satisfied:
(i) The SCP must be safe to eat.
(ii) The nutritional value dependent on the amino acid composition must be high.
(iii) It must be acceptable to the general public.
(iv) It must have the functionality, i.e. characteristics, which are found in common staple foods.
(v) The economic viability of the SCP process is extremely complex and is yet to be demonstrated.