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)

Aspergillus fumigatus

Aspergillus niger

Paecilomyces varioti

The increasing popularity of myco-protein because of the following reasons:-

• Some of the filamentous fungi grow as fast as most of the single celled organism;
• The finished product of filamentous fungi is fibrous in nature and can be easily converted into various textured foods. In comparison, protein is extracted from single celled organisms and spun into fibrous form;
• Filamentous fungi have a greater retention time in the digestive system than single celled organisms;
• Protein content can be as high as 35-50 per cent with comparatively less nucleic acid than single celled organism;
• Digestibility and net protein utilization without any pretreatment is higher than single celled organisms;
• The overall cost of protein production from filamentous fungi is more economical as compared to that of single celled organism;
• Filamentous fungi have greater penetrating power into insoluble substrates and are therefore, more suitable for solid state fermentation of lignocellulosic materials;
• Most of filamentous fungi have a faint mushroom like odor and taste which may be more readily acceptable as a new source of food than the yeast odor and green color associated with yeasts and algae respectively;
• The biomass produced by filamentous fungi can be used as such without any further processing because it provides carbohydrates, lipids, minerals, vitamins and proteins. In addition, a nucleic acid content of fungal protein is lower than that of yeast and bacteria.

While, the disadvantages of fungal used as mycoprotein are:-

• Filamentous fungi show slow growth rate than yeasts and bacteria.
• There is contamination risk.
•  Some strains produce mycotoxins and hence they should be screened. 

 Growth Conditions

The following factors (like bacteria) affect the growth of moulds :  

1.  carbon, nitrogen (C:N) ratio is required to be in the range of 5:1 to 15:1;  
2. ammonium salts are used as a source of nitrogen in continuous culture and phospheric acid for phosphorus. Moreover, most of fungi, for their growth require minerals, such as potassium, sulfur, magnesium, calcium, iron, manganese, zinc, copper and cobalt. Their concentration differs with respect to species;   
3. pH of growth medium ranges from 3.0 to 7.0 but pH 5-6 or below is desirable for most of fungi because bacterial contaminants do not grow;   
4. temperature ranges from 25°C to 30°C with certain exceptions;   
5. oxygen is required for good growth of fungi. During agitation, mycelial mat forms pellets.

Quorn salad

      (a)  Myco-protein

Myco-protein is a product produced from a selected strain of fungus within the genus Fusarium. Fusarium graminearum is the conidial stage of the Ascomycote fungus Gibberella zeae. The fungus exists mainly as a saprobiont in soil, although it is capable of parasitising wheat and other cereals. It has a mycelium of narrow, branched and septate hyphae. This basis for a naturally fibrous (and therefore 'chewy') texture has been exploited in the formulation of meat analogues, which enables it to be used as the major ingredient in a range of meat alternative products marketed by Marlow Foods under the Quorn ™ brand name.

Table 2: Nutritional analysis of freshly-harvested Quorn^TM mycoprotein:

Constituent	Mass (g per 100g)
Protein	11.8
Dietary fibre	4.8
Fat	3.5
Carbohydrate	2.0
Sodium	0.24
Cholesterol	0.0
Water	75.0

(The remaining mass includes a wide variety of minerals and vitamins, particularly zinc and vitamin B 12, as well as compounds such as nucleic acids).

Production of myco-protein represents a more efficient conversion of carbohydrate than production of animal protein, although it is less efficient than direct consumption of the plant foods. 

Protein source
	myco-protein	chicken	pork	beef	wholemeal flour
Protein yield (g) from 1000g of plant carbohydrate	136	49	41	14	157 (in addition to carbohydrate!)

Conclusion

Fungi have been influencing human affairs for thousands of years, whether as a direct food source, as a medicine, or in a food process. Fungi are of excellent value nutritionally, and of great importance to vegetarians.  Edible mushrooms have high protein content, and are an excellent source of fibre, vitamins, and some minerals.  The result is a protein extract with high amino acid content potentially favourable for application to human nutrition.  One particularly successful model was that of myco-protein, marketed as Quorn^TM.  Quorn is now available in supermarkets, marketed as a high-protein, low-fat, cholesterol-free ‘meat alternative’.  When it comes to fungi as a food source, many people are apprehensive and much education is needed before the true nutritional value of such a cheap, readily available food source can be fully realised.

References:

Bhalla, T.C., Sharma, N.N., and Sharma, M., 2007. Production of Metabolites, Industrial enzymes, Amino acid, Organic acids, Antibiotics, Vitamins and Single Cell Proteins. National Science Digital Library, India.

Kavanagh, K., 2005. Fungi: Biology and Applications. England: John Wiley and Sons Ltd, pg 102-104.



By Bee Wen