Classification knowledge of solid state fermentation
1. Traditional solid state fermentation and modern solid state fermentation
Although solid-state fermentation has its unique advantages compared with liquid fermentation, there are still many shortcomings. In particular, traditional solid-state fermentation is synonymous with ancient and backward processes in the fermentation industry. Even in textbooks for fermentation engineering or biochemical engineering, solid-state fermentation is rarely mentioned. The key condition of modern fermentation technology is pure large-scale intensive cultivation. With the development of science and technology and the impact of sustainable development, domestic and international attention has been paid to the research and development of solid-state fermentation, and great progress has been made. Therefore, according to whether the solid microbial culture can be realized in the solid fermentation process, it is divided into traditional solid state fermentation and modern solid state fermentation. Modern solid-state fermentation is to give full play to the advantages of solid-state fermentation. In view of the problems existing in traditional solid-state fermentation and adapting it to the development of modern biotechnology, large-scale cultivation of purebred microorganisms can be realized.
Second, the form of solid state fermentation
1. Classification according to the condition of microorganisms and the product conditions formed
Solid-state fermentation can be carried out in many different forms. Depending on the conditions of the microorganisms used and the product conditions formed, solid-state fermentation can be divided into natural enrichment solid-state fermentation, enhanced microbial mixed solid-state fermentation, limited microbial mixed solid-state fermentation, and single-bacterial solid-state pure Fermentation.
Natural enrichment Solid-state fermentation refers to the enrichment and mixing fermentation process carried out by microorganisms in nature and by continuously succeeding microorganisms. Typical examples are traditional koji and soy sauce, pickled raisins, tobacco fermentation, tea fermentation, silage, composting, and the like. It does not require artificial inoculation of microorganisms. The microorganisms that need to be fermented mainly depend on the natural microflora in the local air and materials. Many microorganisms are succeeded into a small ecological environment that is most suitable for growth metabolism or symbiotic cooperation. Its microbial enrichment zone is not only related to the natural microflora in the local air and materials, but also closely related to the natural changes of the small ecological environment.
Enhanced Microbial Mixed Solid-state Fermentation refers to the mixed fermentation process carried out on the basis of natural enrichment of solid-state fermentation, based on the microbial metabolic mechanism that is partially controlled by humans, artificially inoculated with microbial inaccurate enriched cultures or specific microbial cultures. . In addition to the application of biogas fermentation and liquor fermentation, the enhanced microbial mixed solid-state fermentation also shows its advantages in the fields of oil recovery, hydrometallurgy and food fermentation. In the long-term scientific research and production practice, people have continuously discovered that many life activities and their effects are carried out by the joint action of two or more kinds of organisms in the same environment, even if they cannot be singularly or weakly. . For example, waste treatment, degradation of fiber ropes and essential substances, production and utilization of methane, etc. None of the microbes in nature exist alone, and it is difficult to reflect their true activities by pure culture alone. Therefore, strengthening microbial mixed solid-state fermentation microbial resources has a very broad application prospect.
Defined microbial mixed solid-state fermentation is based on the understanding of microbial interactions and community. It is known and determined to inoculate mixed-cultured microorganisms. Usually, two or more purified and purified microbial species are used, simultaneously or sequentially. The solid state fermentation process carried out in the same sterile medium without contamination. The use of microorganisms by humans has undergone two stages of natural mixed culture to pure culture. Pure culture technology has enabled researchers to get rid of the complex situation of multiple microbes coexisting, and to study single-purpose strains without interference, thus enriching people. Knowledge of the morphological, physiological and genetic properties of microorganisms. However, in long-term experiments and production practices, it has been continuously discovered that many important biochemical processes cannot be performed by a single microbial organism or can only be performed weakly, and must be co-cultured by two or more microorganisms. Although the role of microbial mixed culture in many fields has been fully affirmed, some of the results have been successfully applied in practice, but the research on the interrelationship and mechanism of bacteria in most mixed bacteria systems is not deep enough. Therefore, the screening and combination of strains with synergistic relationship is still a random process, lacking effective theoretical guidance, and can not effectively coordinate the relationship between bacteria to achieve the best ecological level for the already applied mixed culture system. To maximize the effect. This seriously hinders the development and application of mixed bacteria culture. Therefore, if we study the relationship between the mixed bacteria and the synergistic mechanism from the physiological, metabolic and genetic perspectives, there will be a huge breakthrough in the theory and application of mixed bacteria culture. With the deepening of applied research in various aspects of mixed culture, people are no longer satisfied with the traditional reaction mode, and have begun to introduce some new bioengineering technologies to make research in this field more dynamic. Immobilization of mixed bacteria by immobilized cell technology can make the reaction system use multiple times, reducing costs and increasing efficiency, which makes sense in practical applications. The use of cell fusion technology and genetic engineering technology to construct engineering bacteria from microorganisms with mutual or symbiotic relationship can make the engineering bacteria not only have the function of mixed culture, but also possess the advantages of pure nutrient requirements, stable physiological metabolism, easy regulation and so on. A very promising research direction.
Single-cell solid-state pure-fermentation is established on the basis of pure culture and plays a significant role in breeding improved varieties, maintaining physiological activity and stability in metabolic processes. It plays an important role in expanding the application range and potential of solid-state fermentation, and it is also an important direction for solid-state fermentation.
2. Classification according to the nature of solid-state fermentation solid phase According to the nature of solid-state fermentation solid phase, solid-state fermentation can be divided into two types. One is a solid-state fermentation method using crops (such as bran, bean cake, etc.) as a substrate. These substrates are both a solid phase component in the solid state fermentation process and a nutrient for microbial growth, which can be referred to herein as a conventional solid state fermentation process (or solid substrate substrate solid state fermentation). Another solid-state fermentation method uses an inert solid carrier as a solid phase for solid-state fermentation. The nutrient for microbial growth is a culture solution adsorbed on a carrier. This fermentation method is called inert carrier adsorption solid-state fermentation.
The medium used for solid state fermentation of the substrate substrate is a primary crop product that serves both the solid phase and the microbial growth, such as bran, potato, millet, bean cake, and other starch products containing starch and cellulose. The solids employed in the second solid state fermentation are inert carriers which may be either natural or artificially divided. These carrier materials are hemp, perlite, polyurethane foam, sucrose slag, and polystyrene.
A major disadvantage of solid-state substrate solid-state fermentation is that the carbon source is a structural component. During the microbial fermentation process, the medium is decomposed, the substrate is easily agglomerated, and the porosity is also reduced. The shape and physical properties have changed, reducing mass transfer and heat transfer during fermentation. For example, in the fermentation process, the degradation of starch and the volatilization of water during the fermentation process may cause the solid substrate to deform and agglomerate, resulting in mass transfer and heat transfer being affected. The solid carrier having a stable structure acts as a solid phase for solid-state fermentation to overcome this disadvantage, thereby facilitating the growth of microorganisms and the increase in product yield. For example, when polyurethane foam is used as a carrier to adsorb solid-state fermentation nuclease P1, the yield and vigor are 9 times and 4 times higher than that of bran solid-state fermentation, respectively.
In addition, the inert carrier adsorption solid-state fermentation has the advantages of simple product extraction compared with the solid substrate solid-state fermentation. The extracellular product can be easily extracted from an inert carrier, and the resulting product contains less impurities, and the carrier can be reused. For example, when polystyrene is used as a carrier to produce L-glutaminase from the ribs, the product is less viscous than the product obtained by solid-state fermentation of the wheat bran powder. In addition, the former product contains no protein contaminants, while the latter contains excess amylase and cellulase.
Compared with the solid substrate substrate solid state fermentation, the inert carrier adsorption solid state fermentation has many other advantages, such as: able to properly adjust the nutrient composition of the medium; easy to understand the components in the product and analyze it, thereby facilitating the fermentation process Control and dynamics research and model building.
(Zhenjiang Gree Bioengineering Co., Ltd.: http://)
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