Production of enzymes from rice husks and wheat straw in solid state fermentation

In Europe, the agricultural wastes represent a significant potential for the development of biorefineries in different sectors such as cereals. The residues from the processing of grains are about 11 million tons/year of dry basis (Di Biasi et al., 1997). Recovery of phytochemicals as well as the energetic valorization of the plant matrixes needs the demolition of the wall cell plants. Over the past 30 years, it has become clear that research on the degradation of lignocellulose by fungi may lead to other industrial applications (Crawford and Crawford, 1980). Hydrolitic demolition by lignocellulosic enzymes is one of the most studied approach. In recent years, SSF has received more and more interest from researchers, since several studies for enzymes (Pandey et al., 1999), flavours (Ferron et al., 1996), colourants (Johns and Stuart, 1991) and other substances of interest to the food industry have shown that SSF can give higher yields (Tsuchiya et al., 1994) or better product characteristics than submerged fermentation (SmF) (Acuña-Argüelles et al, 1995). Using of agro-industrial residues as substrates in SSF processes provides an alternative avenue and value-addition to these otherwise under- or non-utilized residues. Solid-state fermentation (SSF) has been defined as the fermentation process which involves solid matrix and is carried out in absence or near absence of freewater; although, the substrate must possess enough moisture to support growth and metabolism of the microorganism. The solid matrix could be either the source of nutrients or simply a support impregnated by the proper nutrients that allows the development of the microorganisms. Fungi and yeast were termed as suitable microorganisms for SSF according to the theoretical concept of water activity, where as bacteria have been considered unsuitable (Chinn et al., 2007). On one hand, by utilizing the low cost agricultural residues, SSF adds on to economic feasibility of the process (Robinson and Nigam, 2003) and on other hand it solves the problem of its disposal which otherwise cause pollution (Singhania et al., 2009). Enzymes are among the most important industrial products obtained for human needs by microbial sources; in fact, a large number of industrial processes in the areas of industrial, environmental and food biotechnology utilize enzymes at some stage or the other. Solid state fermentation shows increasing interest for the production of enzymes, specially where the raw fermented waters may be used directly as enzyme sources (Pandey et al., 1999). White rot fungi such as Pleurotus ostreatus produce a wide range of extracellular enzymes to degrade complex lignocellulosic substrates into soluble substances that can be used as nutrients (Giardina et al., 1995; Marzullo et al., 1995). The objective of this study is to induce the production of lignocellulosic enzymes through the growth Pleurotus ostreatus in solid state fermentation using agro-food wastes as substrates: rice husks and wheat straw