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ABSTRACT Starting with a brief history of solid-state fermentation (SSF), major aspects of SSF are reviewed, which include factors affecting SSF, biomass, fermentors, modeling, industrial microbial enzymes, organic acids, secondary metabolites, and bioremediation. Physico-chemical and environmental factors such as inoculum type, moisture and water activity, pH, temperature, substrate, particle size, aeration and agitation, nutritional factors, and oxygen and carbon dioxide affecting SSF are reviewed. The advantages of SSF over Submerged Fermentation (SmF) are indicated, and the different types of fermentors used in SSF described. The economic feasibilities of adopting SSF technology in the commercial production of industrial enzymes such as amylases, cellulases, xylanase, proteases, phytases, lipases, etc., organic acids such as citric acid and lactic acid, and secondary metabolites such as gibberellic acid, ergot alkaloids, and antibiotics such as penicillin, cyclosporin, cephamycin and tetracyclines are highlighted. The relevance of applying SSF technology in the production of mycotoxins, biofuels, and biocontrol agents is discussed, and the need for adopting SSF technology in bioremediation of toxic compounds, biological detoxication of agro-industrial residues, and biotransformation of agro-products and residues is emphasized.
KEYWORDS solid-state fermentation, biomass, fermentors/bioreactors, modeling, industrial enzymes, organic acids, secondary metabolites, bioremediation.
I. INTRODUCTION
Solid-state fermentation (SSF) is defined as a fermentation process in which microorganisms grow on solid materials without the presence of free liquid.1 In SSF, the moisture necessary for microbial growth exists in an absorbed state or complexed within the solid matrix. Although most workers consider solid-state and solid-substrate fermentation essentially one and the same, Pandey et al.2 have distinguished these two as separate processes. According to them, solid-substrate fermentation includes those processes in which the substrate itself acts as the carbon source, and occurring in the absence or near-absence of free water, whereas solid-state fermentation is defined as any fermentation process occurring in the absence or near-absence of free water, employing a natural substrate or an inert substrate as solid support. The term SSF has also been defined in different ways. Thus, Hasseltine3 described it as the fermentation where the substrate is not liquid. While Aidoo et al.4 describe SSF as a fermentation process occurring in solid or semisolid substrate, and in a nutritionally inert solid support, Raimbault and Alazard5, Lonsane et al. and Soccol7 have defined it as a...