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  Section: General Biotechnology / Microbial Biotechnology
 
 
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Single Cell Protein (SCP) and Mycoprotein

 
     
 

Production of Yeast Biomass

In Primary Metabolites, much has been discussed about the use of yeasts in fermentation since centuries (see Alcohols). Consumption of baker's yeast (S. cerevisiae) as food in Germany during World War I increased its importance. Since then, rapid development took place in biotechnological applications of S. cerevisiae, as far as culture development, process optimization and scale up of products are concerned. World production of yeast biomass is of the order of 0.4 million metric tonnes per annum including 0.2 million tonnes baker's yeast alone.

 

Yeasts synthesize amino acids from inorganic acids and sulphur supplemented in the form of salts. They get carbon and energy sources from the organic wastes, e.g. molasses, starchy materials, milk whey, fruit pulp, wood pulp and sulphite liquor.

 

A comparative composition of nutrients is given in Table 18.3. It is obvious that biomass of S. cerevisiae produced on sugarcane molasses differs from that of bear. Yield of yeast biomass is greatly affected by many factors similar to bacteria. Yield corresponds to growth nutrients, organic wastes, temperature, culture, oxygen, etc. Yield of yeasts is given in parentheses in Table 18.2. Bennett et al. (1969) have given the typical equations for the growth of yeasts on carbohydrates or hydrocarbons:

Carbohydrates :

8n CHO + 0.8 nO2 + 0.19n NH4 + trace elements n(CH1.7O95N0.12 Ash) + 0.8n CO2+1.3 nH2O + 80,000n KCal.


Hydrocarbons:

2nCH2+2nO2+0.19n NH4+ trace elements n(CH1.7O0.5N0.19 Ash) + nCO2 + 1.5 H2O + 200,000n KCal.

 

Factors Affecting the Yield of Yeast Biomass

Like bacteria, growth and yield of yeasts are also affected by the following factors: (i) organic substrate and nitrogen ratio (optimum C : N ratio favoring high protein content should be between 7:1 and 10:1); (ii) pH of nutrient medium (pH should be in the range of 3.5 to 4.5 to minimize growth of bacterial contaminates); (iii) temperature (it differs from organism to organism). Most yeasts have specific growth rate in the range of 30°C to 34°C. Some strains also grow in the range of 40-45°C; (iv) oxygen (for growth on carbohydrates), O2 required should be 1 g/g of dried cells, and for growth on n-alkanes it should be about 2 g/g dried cells); (v) maintenance of sterile condition through out the process and (vi) suitable strain of yeast.
 

Content

Advantages of producing microbial protein

Microorganisms use as single cell protein (SCP)

Substrates used for the production of SCP

Nutritional values of SCP

Genetic improvements of microbial cells

Production of algal biomass

 

Factors affecting bio­mass production

 

Harvesting the algal biomass

 

Spirulina as SCP, cultivation and uses

Production of bacterial and actinomycetous biomass

 

Method of production

 

Factors affecting biomass production

 

Product recovery

Production of yeast biomass

 

Factors affecting growth of yeast

 

Recovery of yeast biomass

Production of fungal biomass (Other than Mushrooms)

 

Growth conditions

 

Organic wastes as substrates

 

Traditional fungal foods

 

 

Shoyu

 

 

Miso

 

 

Sake

 

 

Tempeh  

Mushroom culture

 

Historical background

 

Present status of mushroom culture in India

 

Nutritional values

 

Cultivation methods

 

 

Obtaining pure culture 

 

 

Preparation of spawns

 

 

Formulation and preparation of composts

 

 

Spawning, spawn running and cropping

 

Control of pathogens and pests

 

Cultivation of paddy straw mushroom

 

Cultivation of white button mushroom

 

Cultivation of Dhingri (Pleurotus sajor-caju)

 

Recipes of mushroom


Recovery of Yeast Biomass

Yeast cells are small in size (5-8 m), the density of which reaches to 1.1 g/ml. Post-fermentation treatment of food yeast is shown in Fig. 18.2. Yeast cells are recovered by decantation-centrifugation (including washing) drying treatment methods. After washing undesirable traces of medium are removed which are again recycled for economic reasons. As a result of final harvesting by rotary vacuum filter a cake containing 20-40 per cent dry matter is obtained which is then dried to get a product of 6-10 per cent water content (Riviere, 1977).
  Outline of treatment and recovery of yeast cells.
 

Fig. 18.2. Outline of treatment and recovery of yeast cells.

 
     
 
 
     



     
 
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