Solid State Fermentation: A handy Technology for Microbial cultivation
Solid state fermentation (SSF) is a technology which is used for cultivation and production of micro-organisms onto a solid surface in presence of very less or no free water. The solid substrate used in SSF resembles the natural habitat of some of the microbes. The substrate which are used in this technology are mostly of two types, one is nutritional substrate and other is inert material. In case of natural substrates, the substrate itself provides the required nutrients for growth and development of the microbes. Commonly used substrate are cereal husk, oil cakes, residual biomass generated in agriculture sector, etc. Inert materials are the one which provides supports for the microbial adherence on its surface. The inert materials have to be provided with additional source of nutrients.some of the commonly used inert materials are silica, hydrated magnesium silicate salts like Talc, Polyurathrane foam, etc. Solid state technology provides an edge over submerged technology because of the cost and energy requirement associate with it is significantly. Downstream processing is much simpler. Some of the hurdles that limits the use of this technology is difficulty in maintaining its physio-chemical parameters like pH and temperature. This can be solved by automating the process by using a buffered systems and using a temperature regulators. Other limiting factors associated with solid state fermentation are uneven distribution of nutrients and scale-up procedure. Solid substrates generally provide a good dwelling environment to the microbial flora (bacteria, yeast and fungi). Filamentous fungi are best studied for Solid state fermentation because they have the capacity to grow on the surface of the substrate particles. Since a decade, extensive research on SSF are being carried out to valorise the agricultural residues by using micro-organisms. India being the second largest Food and Agriculture producers, the waste generated in this process can be valorised for generation of industrially important products. Apart from enzymes, agri waste can also be used for generating Bioenergy and Biofuels. Several approaches have been applied to resolve the issues related to Solid state fermentation. Modelling could be a good tool for scale-up studies but such results need to be validated experimentally. Thus, continuous efforts would be needed to develop SSF as feasible technology for production of microbial products on commercial scale in equivalent terms to liquid fermentation technique.