Biochemical Engineering Journal (v.13, #2-3)


BEJ Keywords (II).

Preface by Ashok Pandey (79).

Solid-state fermentation by Ashok Pandey (81-84).
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.
Keywords: Solid-state fermentation; General aspects; Biochemical engineering aspects; Modelling; Design of bioreactor;

The role of water in solid-state fermentation by Patrick Gervais; Paul Molin (85-101).
Keywords: Solid-state fermentation; Solute diffusion; Water;

Evidence for the occurrence of an oxygen limitation during soil bioremediation by solid-state fermentation by Julien Troquet; Christian Larroche; Claude-Gilles Dussap (103-112).
Bioremediation methods are a promising way of dealing with soil and subsoil contamination by organic substances. This biodegradation process is supported by micro-organisms which use the organic carbon from the pollutants as energy source and cells building blocks. The scope of this work is to study the main parameters of the process and the physical limiting steps. Several ground samples from an actual petroleum hydrocarbon contaminated site have been tested. Four fixed bed column reactors and one rotating fermentor are used, enabling the study of the influence of different operating variables on the biodegradation kinetics. The stoichiometric equation for bacteria growth and pollutant degradation has been established, allowing the determination of mass balances. Biodegradation monitoring is achieved by continuously measuring the emissions of carbon dioxide. Biodegradation rates and pollution load decrease in the two kinds of bioreactors are also compared.
Keywords: Bioremediation; Polluted soils; Biodegradation; Aerobic processes; Aeration; Oxygen transfer;

Solid state fermentation has gained renewed attention not only from researchers but also from industry. This technique has become a more and more attractive alternative to submerged fermentation for specific applications due to the recent improvements, especially in the design. This paper reviews the various reactor designs and focuses on the differences between lab-scale and industrial-scale designs. It highlights the main designs that have emerged over the last 10 years and the potential for scaling-up for each category of reactor.
Keywords: Solid state fermentation; Bioreactor design; Engineering; Scale-up strategies;

Some engineering aspects of solid-state fermentation by K.S.M.S Raghavarao; T.V Ranganathan; N.G Karanth (127-135).
Solid state fermentation which involves growth of microorganisms on moist solid substrates in the absence of free flowing water, has gained considerable attention of late due its several advantages over submerged fermentation. Solid-state fermentation is also finding increased application in the production of enzymes, antibiotics, surfactants, biocides etc. as also for the production of value-added products from wastes. There have been significant additions to the science and engineering knowledge of solid-state fermentations in recent years. This paper aims to present an overview of these developments emphasizing important aspects such as mass and heat transfer, design, scale-up, monitoring and control.
Keywords: Solid-state fermentation; Microorganisms; Mass transfer; Heat transfer; Bioreactor design; Monitoring and control;

Recent developments in modeling of solid-state fermentation: heat and mass transfer in bioreactors by David A. Mitchell; Oscar F. von Meien; Nadia Krieger (137-147).
Mathematical models are important tools for optimizing the design and operation of solid-state fermentation (SSF) bioreactors. Such models must describe the transport phenomena within the substrate bed and mass and energy exchanges between the bed and the other subsystems of the bioreactor, such as the bioreactor wall and headspace gases. The sophistication with which this has been done for SSF has improved markedly over the last decade or so. The current article reviews these advances, showing how the various transport phenomena have been modeled. It also discusses the insights that have been achieved through the modeling work and the improvements to models that will be necessary in order to make them even more powerful tools in the optimization of bioreactor performance.
Keywords: Solid-state fermentation; Bioreactors; Modeling; Packed-bed bioreactors; Rotating-drum bioreactors; Gas–solid fluidized bed bioreactors; Tray bioreactors;

Evolutionary operation (EVOP) is an important tool for the optimization of a complex system like solid state fermentation (SSF) whose objective or response function is influenced by a large number of physico-chemical parameters. EVOP takes care of all the variable parameters at a time to evaluate statistically their effects including interaction effects on the response function and finally select the optimum conditions based on the decision making analysis to arrive at the maximum or minimum.
Keywords: EVOP; SSF; Optimization;

Advantages of fungal enzyme production in solid state over liquid fermentation systems by Gustavo Viniegra-González; Ernesto Favela-Torres; Cristobal Noe Aguilar; Sergio de Jesus Rómero-Gomez; Gerardo Dı́az-Godı́nez; Christopher Augur (157-167).
The present paper attempts to explain why enzyme production in solid-state fermentation (SSF) is higher than in submerged fermentation (SmF). Recent work done in our laboratory [Biotechnol. Lett. 22 (2000) 1255; J. Ind. Microbiol. Biotechnol. 26 (5) (2001) 271; J. Ind. Microbiol. Biotechnol. 26 (5) (2001) 296] related to the production of invertase, pectinases and tannases, by Aspergillus niger grown by SSF and SmF is reviewed. To do such a comparative study, logistic and Luedeking–Piret equations are used in order to estimate the values of the following coefficients: maximal specific growth rate (μ M), maximal biomass level (X M), enzyme/biomass yield (YP /X ) and secondary rate of production, or breakdown (k). It is shown that enzyme productivity is proportional to group, μ M Y P/X X M, corrected by a function of ν=k/Y P/X μ M. In all three cases of enzyme production studied, productivity using a SSF system was higher than in SmF. Studies with invertase resulted in higher values of μ M X M. Studies with pectinases resulted in higher values of Y P/X X M. Studies with tannases resulted in higher YP /X and less negative values of k. Finally, a reaction–diffusion model is presented to try to explain such differences based on micrographic measurements of mycelial aggregates for each kind of fermentation system.
Keywords: Solid state fermentation; Filamentous fungi; Submerged culture; Enzyme production; Proteolysis;

Bioconversion of lignocellulose in solid substrate fermentation by R.P. Tengerdy; G. Szakacs (169-179).
In this review the state of the art of lignocellulose bioconversion by solid substrate fermentation (SSF) is presented. The most important lignocellulolytic fungi and their properties are described, and their application in novel solid state bioreactors with on-line process control is discussed. The most important bioconversion products, biofuels, enzymes, animal feeds, biofertilizers, biopesticides, biopromoters, secondary metabolites, and the economy of their production by SSF is discussed. The use of SSF in the pulp and paper industry and in integrated crop management is illustrated.
Keywords: Lignocellulose; Bioconversion; Solid substrate fermentation;

Engineering aspects of ensiling by Z.G Weinberg; G Ashbell (181-188).
Ensiling is a preservation method for moist forage crops, based on a lactic acid solid-state fermentation. Air is detrimental to silage because it enables the reactivation of detrimental aerobic microorganisms. The present review describes some of the major engineering and physical aspects of ensiling—silo types and the ensiling process—step by step. Issues considered include harvest and chopping, degree of consolidation, permeability to air ingress, sealing, additive application and unloading. Mathematical models that have been developed to simulate the ensiling process are mentioned. Experimentation methods are also described.
Keywords: Anaerobic processes; Food engineering; Forage preservation; Modeling; Silage; Solid-state fermentation;

Solid substrate fermentation at Biocon was originally envisaged for the production of enzymes, used in the food processing industry. The original process developed at Biocon was a hygienically designed automated tray culture process. Plants using this process still continue to run effectively at Biocon, and produce a variety of products meeting and exceeding FCC/JECFA specifications for food products. Biocon recently designed, developed and patented a new bioreactor, the PlaFractor™ (pronounced play-fractor) for carrying out fermentations that use solid matrices—a term covering both nutritive support matrices as well as non-nutritive matrices impregnated with medium.Using the PlaFractor™ process it is now possible to extend the use of solid matrix fermentation for the production of enzymes, biocontrol agents and pharmaceutical products, that require elaborate containment—under precisely defined conditions. The production takes place in computer controlled bioreactors, using complex fermentation control algorithms. All the operations of solid matrix fermentation, i.e. sterilization, cooling, inoculation, fermentation and process control, product recovery and post-fermentation sterilization, are all done in one single equipment, which was not hitherto possible. All the advantages of traditional solid state fermentation, over submerged fermentation, like low energy consumption, low water requirement, high mass transfer coefficient, no foaming, and high product concentrations are retained. In addition, techniques that are important to submerged fermentation, like fed-batch fermentation, process parameter profiling, air and media sterilization, operation under aseptic environments, and ease of handling, can now be easily applied to solid state fermentation, because of the way this bioreactor is designed.A production plant, built around this bioreactor has already been operating for more than a year.
Keywords: Solid state fermentation; Large scale cultivation; Control; Bioreactor; Process integration; Pharmaceuticals;

This paper reviews bioreactor designs and their use for protein production under solid state fermentation (SSF) conditions using various agricultural by-products. The advantages and disadvantages of various bioreactors and their potential for scale-up are described. SSF is proposed as a suitable low-tech strategy for protein enrichment for animal feed by converting a previously low value substance into a more nutritionally valuable one. The use of various substrates and microorganisms for protein enrichment are also listed.
Keywords: Agricultural residues; Bioconversion; Bioreactors; Protein; Solid state fermentation;

Overview of applied solid-state fermentation in Brazil by Carlos R Soccol; Luciana P.S Vandenberghe (205-218).
This review discusses the history and evolution of solid-state fermentation (SSF) in Brazil in the last 15 years. SSF processes and applications are presented here pointing out the advantages and perspectives for the use of this technique. Brazilian economy is strongly dependent on the various kinds of agro-industrial production such as coffee, sugar cane, soybean, etc., which also generates huge quantities of agro-industrial residues such as sugarcane bagasse, apple pomace, coffee husk and pulp, soybean defatted cake and declassified potatoes. Following the global trends on SSF research, since last 15 years the Laboratory of Biotechnological Processes (LPB) of Federal University of Paraná (UFPR) started a very promising journey through the development of SSF processes using agro-industrial residues for protein enrichment, biological detoxification, production of biomolecules such as enzyme, organic acids, food aroma compounds, biopesticides, mushrooms, pigments, xanthan gum, hormones (gibberellic acid (GA3)), etc. The basic aim has been to develop a laboratory scale bioprocess and optimize the production applying biochemical engineering principles.
Keywords: Solid-state fermentation; Cassava bagasse; Coffee husks; Respirometry; Protein enrichment; Organic acids; Mushrooms; Aroma compounds; Gibberellic acid; Enzymes; Proteases; Sugarcane bagasse; Apple pomace; Coffee husk and pulp; Soybean defatted cake; Declassified potatoes;