Current Developments in Biotechnology and Bioengineering

Current Advances in Solid-State Fermentation

Ashok Pandey, Christian Larroche, Carlos Ricardo Soccol

• Publisher: Elsevier
• Year: 2017
• Print ISBN: 9780444639905
• eBook ISBN: 9780444639912
• Topic: Technology & Engineering
• Subtopic: Biotechnology
• Index: Technology & Engineering

Current Developments in Biotechnology and Bioengineering: Current Advances in Solid-State Fermentation provides knowledge and information on solid-state fermentation involving the basics of microbiology, biochemistry, molecular biology, genetics and principles of genetic engineering, metabolic engineering and biochemical engineering. This volume of the series is on Solid-State fermentation (SSF), which would cover the basic and applied aspects of SSF processes, including engineering aspects such as design of bioreactors in SSF. The book offers a pool of knowledge on biochemical and microbiological aspects as well as chemical and biological engineering aspects of SSF to provide an integrated knowledge and version to the readers. - Provides state-of-the-art information on basic and fundamental principles of solid-state fermentation - Includes key features for the education and understanding of biotechnology education and R&D, in particular on SSF - Lists fermentation methods for the production of a wide variety of enzymes and metabolites - Provides examples of the various industrial applications of enzymes in solid state fermentation

Chapter 1

Advances in Solid-State Fermentation

Jorge A.V. Costa¹, Helen Treichel², Vinod Kumar³, and Ashok Pandey^{3 1}Federal University of Rio Grande, Rio Grande-RS, Brazil ²Federal University of Fronteira Sul, Erechim-RS, Brazil ³Center of Innovative and Applied Bioprocessing, Mohali, India

Abstract

Solid-state fermentation (SSF) is a three-phase heterogeneous process, comprising solid, liquid, and gaseous phases, which offers potential benefits for the microbial cultivation for bioprocesses and products development. Over the last two decades, SSF has gained significant attention for the development of industrial bioprocesses, particularly due to lower energy requirement associated with higher product yields and less wastewater production with lesser risk of bacterial contamination. In addition, it is ecofriendly, mostly utilizing solid agro-industrial wastes (resides) as the substrate (source of carbon). SSF processes have enormous potential for many new applications using the bioconversion of agro-industrial residues into biofuels and other high value–added products. SSF offers potential benefits on economic and environmental fronts, with sustainability. This chapter discusses the potential of SSF processes and benefits they offer for the production of industrial processes, including challenges and perspectives.

Keywords

Design of bioreactors; Kinetics; Modeling; Processes and product; Solid-state fermentation

1. Introduction

Solid-state fermentation (SSF) has been known since ancient times in some countries. In SSF, various types of fungi, bacteria, and actinomycetes have been employed for the production of various bioproducts. Classical examples of SSF include the fermentation of rice by Aspergillus oryzae to initiate the koji process and Penicillium roqueforti for cheese production [1]. Nevertheless, the importance of SSF was nearly ignored in Western countries, perhaps after the discovery of penicillin using SmF technology in the 1940s. However, in the last decades, SSF has regained attention due to several biotechnological advantages such as higher fermentation capacity, higher end-product stability, lower catabolic repression, and cost-effective technology.

SSF processes have enormous potential for many new applications using the bioconversion of agro-industrial residues into biofuels and other high value-added products. The agricultural sector is currently undergoing global expansion, especially in relation to crops used for energy production as a strategy to reduce dependence on petroleum and mitigate the effects of climate change. Consequently, a similar expansion is expected in the amounts of agricultural and forestry residues generated [2].

SSF is a three-phase heterogeneous process, comprising solid, liquid, and gaseous phases, which offers potential benefits for the microbial cultivation for bioprocesses and product development. Over the last two decades, SSF has gained significant attention for the development of industrial bioprocesses, particularly due to lower energy requirements associated with higher product yields and less wastewater production with lesser risk of bacterial contamination. In addition, it is ecofriendly, mostly utilizing solid agro-industrial wastes (resides) as the substrate (source of carbon) [3]. SSF has been defined as the bioprocess carried out in the absence, or near-absence, of free water; however, the substrate must possess enough moisture to support the growth and metabolic activity of the microorganism. The solid matrix could be either the source of carbon (and other nutrients), or it could be an inert material to support the growth of the microorganisms on it (with impregnated growth solution).

As has been advocated, the potential of SSF is to provide the cultivated microorganism with an environment as close as possible to its natural environment, from where they are isolated. This apparently is the main reason microbes perform well and give higher product yields in SSF when compared with the liquid fermentation carried out in a closed bioreactor, even with optimal conditions for growth and activity. SSF has continued to build up credibility in biotech industries due to its potential applications in the production of biologically active secondary metabolites, apart from feed, fuel, food, industrial chemicals, and pharmaceutical products, and has emerged as an attractive alternative to submerged fermentation [3–7]. Based on this, the current chapter focuses on SSF process and product development mainly from the last decades.

2. Important Aspects

SSF is governed by several factors, each of which is critical for the technical and economic feasibility of the process development. These include the selection of microorganism and substrate, optimum physical–chemical and biological process parameters, and purification of the desired products, which have been a challenge for SSF [3,8,9]. Other factors that affect the SSF processes include the selection of microorganism and isolation and purification of the end-product, the latter often considered as a challenge for this technology. While fungi and yeast are usually considered suitable microorganisms for SSF according to the theoretical concept of water activity, bacteria have not been so commonly used in SSF processes, although there are several works that [10,11] prove that bacterial cultures can also be well manipulated and managed for SSF processes.

As mentioned earlier, the common use of fungal and yeast cultures for SSF processes has been essentially based on the theoretical concept of water activity, as fungi and yeast have lower water activity (α_w) requirements, typically around 0.5–06 α_w. Bacterial cultures have a higher water activity requirement (around 0.8–0.9 α_w), which makes them not suitable for SSF processes. However, this theoretical concept does not seem to be correct universally as a large number of bioprocesses have been described that are bacterial-based. The choice of the microbe should apparently be linked with the selection of the substrate and product for which it is intended [3,12,13].

Another important point to be considered is the identification of the physiology of the microorganism and the physico-chemical factors where it grows, which are required for its optimal growth and activity. These factors include temperature, pH, aeration, water activity and moisture, bed properties (thickness, porosity), nature of solid substrate employed, including the particle size, and so on. These must be optimized based on factorial design experiments and response surface methodology so as to identify the critical factors and their interactions. Modern biotechnological tools involving artificial neural network (ANN) and genetic algorithm (GA) offer potential advantage for the optimization of bioprocesses, including SSF [3,14,15].

Understanding of heat and mass transfer effects are among the most critical aspects of SSF, which need attention. These pose a challenge for the design and operation of bioreactors and their scale-up for the commercialization of SSF processes. The heterogeneous nature of the substrate (generally agro-industrial residues) poses problem in kinetics and modeling studies. However, from a process-engineering point of view, this is mandatory information for the development of the design of the bioreactors and their operation [4,5,16–18].

Several substrates can be used in SSF, which usually are agro-industrial residues. They serve as a carbon and energy source (also a source of proteins) and provide solid-state conditions in the fermentation. However, such substrates differ greatly in composition, chemical nature, mechanical properties, particle size, water retention capacity, surface area, and so on. These factors affect the overall process design and product development. During the last decades, there have been significant developments on these aspects [3]. Use of agro-industrial residues and by-products as substrates for microbial growth in SSF not only offers economic benefits (cheaper substrates), but also helps in environmental protection and sustainability, since their disposal in the environment otherwise would cause negative environmental impact [19].

The nature of solid substrate is an important factor in SSF; chemical compositions as well as the physical state of such substrates greatly affect microbial physiology, thus in turn affecting the productivities. Additionally, cost and availability of the substrate also play an important role in selection of a substrate for microbial growth. Sometimes the composition of the substrate does not correspond to the nutritive demands of the microorganism, which then requires medium supplementation with external sources of nutrients [20]. In some substrates, accessibility of the nutrients is poor due to the existence of obstinate complexes that hinder and limit the degradative enzymes to use and assimilate nutrients from the media [21]. Generally, SSF on these substrates is promoted by some kind of physical and/or chemical pretreatment. The selection of substrate also depends upon several factors, mainly related with the cost and availability, and thus involves the screening of several agro-industrial residues [5,22,23].

Finally, as mentioned previously, among several critical factors, moisture and water activity are the most important factors affecting SSF processes. Selection of moisture depends on the microorganism employed and also on the nature of substrate. Fungi need lower moisture; ∼40% to 60% moisture is usually sufficient.

3. Challenges in Process Engineering Parameters

There are major challenges that need to be addressed for the successful implementation of SSF technology, in particular for the scale-up, which is often considered a major bottleneck. There are no general rules for guiding the scale-up of SSF bioreactors; therefore, it is necessary to scale-up processes on a case-by-case basis [24,25]. The most important parameters to consider here are the adequate heat and mass transfer within the substrate bed, to monitor online several key process parameters and also to mix the bed adequately without damaging the microorganisms and the substrate particle size of the su...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• Preface
• Chapter 1. Advances in Solid-State Fermentation
• Chapter 2. Advances in Porous Characteristics of the Solid Matrix in Solid-State Fermentation
• Chapter 3. Fungal Growth on Solid Substrates: A Physiological Overview
• Chapter 4. Kinetics of the Solid-State Fermentation Process
• Chapter 5. Design of Bioreactors in Solid-State Fermentation
• Chapter 6. Online Monitoring of Solid-State Fermentation Using Respirometry
• Chapter 7. Bioreactors for the Production of Biological Control Agents Produced by Solid-State Fermentation
• Chapter 8. Solid-State Fermentation for the Production of Lipases for Environmental and Biodiesel Applications
• Chapter 9. Solid-State Fermentation for the On-Site Production of Cellulolytic Enzymes and Their Use in the Saccharification of Lignocellulosic Biomass
• Chapter 10. Solid-State Fermentation for the Production of Proteases and Amylases and Their Application in Nutrient Medium Production
• Chapter 11. Solid-State Fermentation for Laccases Production and Their Applications
• Chapter 12. Agricultural Residues as Animal Feed: Protein Enrichment and Detoxification Using Solid-State Fermentation
• Chapter 13. Secondary Metabolites Production: Physiological Advantages in Solid-State Fermentation
• Chapter 14. Solid-State Fermentation for the Production of Mushrooms
• Chapter 15. Solid-State Fermentation for Food Applications
• Chapter 16. Solid-State Fermentation for the Production of Biosurfactants and Their Applications
• Chapter 17. Solid-State Fermentation for Vermicomposting: A Step Toward Sustainable and Healthy Soil
• Chapter 18. Solid-State Fermentation for the Production of Organic Acids
• Chapter 19. Solid-State Fermentation and Plant-Beneficial Microorganisms
• Index