Bioconversion processes

Fed-batch culture A cell cultivation technique in which one or more nutrients are supplied to the bioreactor in a given sequence during the growth or bioconversion process while the products remain in the vessel until the end of the run. 

The development of bioreactor systems for the production of large-volume chemicals (see Chapter 3) could be the basis for reconsidering the production of biomass in limited quantities for fuel uses. This would require efficient microbial organisms to catalyze fermentation, digestion, and other bioconversion processes, as well as efficient separation methods to recover fuel products from process streams. 

The physical methods include dilution, emulsification, addition of surface active agents, etc. Chemical conversion includes those methods involving carbon rejection and those of hydrogen addition . So far, there has not been any bioconversion process that has accomplished the developmental stage however, there have been some MEOR initiatives, which could be taken as inspiration for upgrading routes. Some of them will be mentioned here as examples, but will be specifically identified as MEOR alternatives. 

The bioconversion process of Acid Orange 7 will be hereby analyzed. This is an incremental study with respect to that due to Lodato et al. [41], based on the operation of an airlift reactor with cells of Pseudomonas sp. 0X1 immobilized on natural pumice (density = 1,000 kg/m3 particle size = 800-1,000 pm). Details regarding the strain, medium, culture growth and main diagnostics of the liquid phase are reported by Lodato et al. [41]. Elemental analysis of dry biomass was obtained by a C/H/N 600 LECO analyzer. 

Qureshi N, Annous BA, Ezeji TC et al (2005) Biofilm reactors for industrial bioconversion processes employing potential of enhanced reaction rates. Microb Cell Fact 4(24) 1-21... 

Enzymes in Biomass Conversion features chapters written by many of the leading international experts from universities, government research laboratories, and enzyme-producing industries. The chapters cover the enzymes of current potential importance to large-scale commercial bioconversion processes. They describe our state of knowledge about enzymes in specific applications, preferred methods for enzyme production, characteristics of the individual enzymes, and recommendations for future research. 

One of the major expenses incurred in the application of enzymes for bioconversion processes is the cost of enzyme production (1). The total cost of production includes the cost of fermentative production as well as downstream processing requirements. Both of these factors must be optimized and integrated for maximum cost-effectiveness. 

Several bioconversion processes were developed to a production scale. These included the use of the precursors iranx-cirmamic acid by Cenex, df-acetamidocinnamic acid by... 

Labuda IM, Goers KA, Keon KA (1993) Microbial bioconversion process for the production of vanillin. In Schreier P, Winterthaler P (eds) Progress in flavour precursor studies analysis, generation, biotechnology. Proceedings of the international conference, Wuerzburg. Allured, Carol Stream, pp 477-482... 

As described above, ECB deacylase catalyzes the cleavage of ECB to produce the important antifungal intermediate ECB nucleus. Both ECB and ECB deacylase are made by fermentation. This section outlines how these fermentations were optimized to create a commercially viable process. Section IV looks at the optimization of the bioconversion process itself. 

The development of the fermentation processes for making the substrate (ECB) and the enzyme (ECB deacylase) has been described briefly in the proceeding section. The development of the bioconversion process itself will be considered in the following section. 

One solution to the above problems would be to purify either the substrate or the enzyme. For example, in the case of ECB, the substrate of the enzyme could be extracted from the cells and then purified by chromatography to remove any impurities that would interfere with the bioconversion processes. The ECB could be left as a solution in a solvent or dried to a powder form. ECB deacylase could also be purified to either a concentrated enzyme solution or solid form. Another option is to immobilize the enzyme or substrate on a suitable support. In the case of ECB deacylase, the advantage would be that the enzyme could be reused and the savings gained would obviously have to be compared with the extra costs of immobilization. The next section looks in more detail at the novel approach of immobilizing the ECB substrate. 

We have discussed how each step in the bioconversion process (e.g., the ECB and ECB deacylase fermentations and the bioconversion) can be improved. The overall improvement in the process is shown in Figure 5. However, with limited resources and time, it is important to focus development efforts on steps that will have the greatest effect on the overall productivity of the process. An excellent way to achieve this is to develop an economic model of the overall process and to use this as shown schematically in Fig. 6. For example, it may be wasteful to focus efforts on improving the yield of the enzyme fermentation if the major cost was due to the ECB fermentation. 

Figure 5 Improvement ofECB bioconversion process due to improvements in the yields of the ECB and ECB deacylase fermentation processes and optimization of the bioconversion process itself.

Figure 6 Overview ofECB bioconversion process optimization.

The development of a commercially viable enzyme process for the production of ECB nucleus was achieved by improving the ECB and ECB deacylase fermentation processes and the bioconversion processes. Increased yields in the fermentation processes were achieved through linked programs for strain improvement and fermentation development. The bioconversion process was improved by the choice of substrate and enzyme conditions and subsequent optimization of operating conditions. An economic model was used to decide where development resources should be focused. 

This session deals with recent progress on pretreatment of lignocellu-losic biomass, the peripheral reactions associated with pretreatment, and assessment of the effectiveness of pretreatment by enzymatic hydrolysis. Pretreatment is an essential element of the integral bioconversion process, and its objective is to enhance the susceptibility of cellulosic substrates to the action of cellulase enzymes. 

A typical wood-to-ethanol bioconversion process consists of at least three major steps pretreatment, hydrolysis, and fermentation. The pretreatment stage has been shown to be the key step to providing a substrate susceptible to the subsequent hydrolysis. Steam explosion is one of the most intensively studied pretreatment methods for bioconversion of softwood materials (6-10). 

Hirschmann, S., Baganz, K., Koschik, I. and Vorlop, K.-D. 2005. Development of an Integrated Bioconversion Process for the Production of 1,3-Propanediol from Raw Glycerol Waters. 

The commercial bioconversion process employs the enzyme nitrile hydratase, which catalyzes the same reaction as the chemical process (Figure 31.15). The bioconversion process was introduced using wild-type cells of Rhodococcus or Pseudomonas, which were grown under selective conditions for optimal enzyme induction and repression of unwanted side activities. These biocatalysts are now replaced with recombinant cells expressing nitrile hydratase. The process consists of growing and immobilizing the whole cell biocatalyst and then reacting them with aqueous acrylonitrile, which is fed incrementally. When the reaction is complete the biocatalyst is recovered and the acrylamide solution is used as is. The bioconversion process runs at 10°C compared to 70°C for the copper-catalyzed process, is able to convert 100 percent of the acrylonitrile fed compared to 80 percent and achieves 50 percent concentration... 

The developments of recombinant DNA techniques will later provide promising approaches of using enzymatic cofactor regeneration in the years to come. The preparation of suitable designer cells will become simpler and new bioconversion processes will be designed. 

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