Solid-state fermentation has emerged as a potential technology for the production of microbial products such as feed, fuel, food, industrial chemicals and pharmaceutical products. Its application in bioprocesses such as bioleaching, biobeneficiation, bioremediation, biopulping, etc. has offered several advantages. Utilisation of agro-industrial residues as substrates in SSF processes provides an alternative avenue and value-addition to these otherwise under- or non-utilised residues. Today with better understanding of biochemical engineering aspects, particularly on mathematical modelling and design of bioreactors (fermenters), it is possible to scale up SSF processes and some designs have been developed for commercialisation. It is hoped that with continuity in current trends, SSF technology would be well developed at par with submerged fermentation technology in times to come.

Solid-state fermentation

Trametes hirsuta and a purified laccase from this organism were able to degrade triarylmethane, indigoid, azo, and anthraquinonic dyes. Initial decolorization velocities depended on the substituents on the phenolic rings of the dyes. Immobilization of the T. hirsuta laccase on alumina enhanced the thermal stabilities of the enzyme and its tolerance against some enzyme inhibitors, such as halides, copper chelators, and dyeing additives. The laccase lost 50% of its activity at 50 mM NaCl while the 50% inhibitory concentration (IC(50)) of the immobilized enzyme was 85 mM. Treatment of dyes with the immobilized laccase reduced their toxicities (based on the oxygen consumption rate of Pseudomonas putida) by up to 80% (anthraquinonic dyes). Textile effluents decolorized with T. hirsuta or the laccase were used for dyeing. Metabolites and/or enzyme protein strongly interacted with the dyeing process indicated by lower staining levels (K/S) values than obtained with a blank using water. However, when the effluents were decolorized with immobilized laccase, they could be used for dyeing and acceptable color differences (DeltaE*) below 1.1 were measured for most dyes.

https://repositorium.sdum.uminho.pt/bitstream/1822/2402/1/28.pdf

Decolorization and detoxification of textile dyes with a laccase from Trametes hirsuta.

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.

Solid-State Fermentation Systems—An Overview

Recent process developments in solid-state fermentation

Engineering aspects of solid state fermentation

Pectolytic enzyme was produced on large scale by solid state fermentation using Aspergillus carbanerius CFTRI 1048 strain on wheat bran medium. Effect of fermentation time (up to 25 h), temp. (chamber temp., 26-26.5 degree C, tray temp. 30 degree C), steaming and sterilization of the bran on production of enzyme, and the influence of extraction (enzyme recovery) temp. were assessed. Fermentation for 21 h with a tray temp. of 30 degree C gave max. production of enzyme. Steaming of wheat bran at 15 Pa for 45 min was needed to get good results. Extraction of enzyme by water from mouldy bran at 25-28 degree C and clarification of the enzyme by plate and frame filter press gave satisfactory results. The enzyme could be precipitated using ethanol with a contact time of 5 min (contact times up to 6 h) were tested, and the optimum concn. of ethanol in the alcohol mixture needed for max. recovery was 50% (concn. tried 30-70%). Precipitation at 4 degree C gave 25% more enzyme recovery than at 25-28 degree C. When suspended in buffer of pH 7 the enzyme precipitate lost its activity rapidly at 25-28 degree C and at 4 degree C; the dried powder lost about 6.5% activity in 37 days, vs. 8% for the original extract.

Large scale production of pectolytic enzyme by solid state fermentation

A large scale solid state fermentor of 150 tray capacity is designed with appropriate control system. It gave better productivity even at higher scale of operation as compared to lab and large scale units of similar type and largely overcomes some operational problems.

S. V. Ramakrishna

Papers

Engineering aspects of solid state fermentation

Large scale production of pectolytic enzyme by solid state fermentation

Design of solid state fermentor for production of fungal metabolites on large scale.