Influence of Process Parameters on the Production of Metabolites in Solid-State Fermentation

Solid-state fermentation (SSF) involves the growth of microorganisms on moist solid substrates in the absence of free water. This low moisture content makes the SSF different from submerged fermentation. Unlike the situation in submerged fermentation there is no systematic study guiding the design and operation of large scale SSF with proper controls. The understanding and modeling of microbial growth kinetics and transport phenomena play important roles in the SSF. The design of bioreactors from tray type to stirred tank is discussed. The packed bed, rotating drum, rocking drum, fluidized bed and stirred tank reactors are used in SSF with and without modifications. The parameters like pH, temperature, agitation and aeration also need to be controlled. There is a large gradient of temperature throughout the trays. By manipulating the nitrogen source requirement, the pH of the system is generally controlled. The different factors that control the agitation and aeration in the SSF are discussed. Finally the advantages and disadvantages of SSF compared to submerged fermentation were mentioned. Moreover, such understanding is very much required in the design, scale up and process control in SSF. This paper deals with the influence of environmental parameters such as airflow rate, temperature, pH, substrate concentration and other physico-chemical parameters on the production of specific metabolites.