Solid state fermentation water activity

The operating conditions are very important for efficient cellulase production via solid-state fermentation. The effects of operating conditions, such as temperature, water content and water activity, pH, aeration and substrate composition, on the cellulase production by solid-state fermentation will be discussed in this section. 

In the solid-state fermentation process, the water activity is variable because of evaporation and metabolism. In order to keep the water activity constant, the humidity of the supplied air should be controlled or a humidifier should be installed in the fermentor. The relationship between the water activity within the solid substrate and the equilibrium relative humidity (ERH) of the surrounding air can be expressed as ... 

Wheat bran, which contains cellulose, protein and other nutrients, is an excellent medium for solid-state fermentation [25,47]. Wheat bran is also widely used in other fermentation industries but is still too expensive for economic cellulase production. Agricultural residue is cheaper. For example [30,48], after pretreatment by 4 % NaOH at 121 °C for 0.5 -1.0 h, wheat straw was used as raw material. After mixing with nutrient salts, adding water to a water content of 80%, then adjusting the pH to 5.8, the medium was used for solid-state fermentation. The final cellulase activity was reported to be as high as 200-430 FPIU per gram of cellulose. Deschamps et al. [49] used a mixture of wheat straw and bran (80 20) as raw materials for solid-state fermentation the... 

Parameters to describe a solid-state fermentation process for cellulase production include physical properties such as temperature, pH, humidity and water activity, particle size, pile and real densities, pore size and porosity, etc. chemical components such as medium composition, gas-phase composition, amount and properties of microorganisms, activities of cellulases, etc. and kinetic para-... 

A. (2004) Polyol accumulation by Aspergillus oryzae at low water activity in solid-state fermentation. Microbiology, 150, 1095-1101. 

The sohd-state fermentation for cellulase production is an aerobic process therefore, aeration is necessary for cell growth and cellulase formation. In addition, aeration is important in order to maintain humidity, to remove gaseous metabolites, such as COj, as well as to remove the heat of metabolism [42,43]. In a large-scale solid-state fermentor, aeration is so important that it must be controlled carefully. The aeration method and the flow rate as well as the temperature and humidity of the air supply must be regulated to avoid sudden changes in temperature and water activity of the solid medium [29,31]. 

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