Fungal solid state fermentation on agro-industrial wastes for industrially relevant enzymes production

12 1.1 Scientific background Large amounts of enzymes are needed to make their application feasible at industrial scale, thus considerably increasing costs of industrial processes. Reducing enzymes costs is a key research priority to make industrial bioprocesses competitive in comparison to the conventional ones. From this point of view, solid state fermentation (SSF) holds tremendous potential for the production of industrial enzymes, because of its economical advantages. SSF is defined as a fermentation process taking place on moist solid supports, in absence or near absence of free water (Couto Rodriguez et al, 2005). The aim of the SSF is to bring the cultivated microorganisms into tight contact with the substrate and thus achieve the highest substrates concentration for the fermentation (Hölker et al, 2004). The materials used in the SSF can be inert supports, having only attachment function and requiring nutrient supplementation, or non-inert supports, named also support-substrates, that provide both a source of nutrients and attachment (Couto Rodriguez, 2008). For development of any SSF process there are some important aspects that must be considered, such as the choice of microorganisms and substrates. Bacteria, fungi and yeasts can be used in SSF, even if the former must be previously manipulated because of their high water activity requirement (Pandey, 2003). Filamentous fungi are the most important group of microorganisms used in SSF process. The hyphal mode of fungal growth and their good tolerance to low water activity and high osmotic pressure conditions make fungi efficient and competitive in natural microflora for bioconversion of solid substrates. As a matter of fact, the hyphal mode of growth gives a major advantage to filamentous fungi over unicellular microorganisms in colonization of solid substrates and utilization of available nutrients. The basic mode of fungal growth is a combination of apical extension of hyphal