Down-stream processing

You are now familiar with the major characteristics of organisms that are useful for SCP production, and the types of substrates on which they can be grown. We are now going to consider in detail the processes that have been developed. Some of these processes have been developed only as far as the pilot scale, and have not reached commercial operation. Others have reached full production scale but have subsequently failed, for a variety of reasons. These have been included as well as the successes, as they show you the variety in the technology of SCP production, and also show how economic and political factors influence the success and failure of processes. These processes might also become useful and economic some time in the future. Emphasis will be put on the technology involved in the fermentation and down-stream processing of each process. 

In parallel with these studies, developments were underway to find the most economical method of large-scale culture and down-stream processing. The biochemistry of methanol and ammonia utilisation by MethylopHlus methylotrophus was also studied to pinpoint possibilities for manipulation. 

Hoare M, Khan MR, DunnUl P (1992) Interfacial damage to proteins during intensive mixing in fermentation and down stream process. In Van Den Tweei WJJ, Harder A, Buitelaar RM (eds) StabUity and stabilization of enzymes, Proc Inter Sym, The Netherland, Elsevier Sci... 

Three-phase slurry reactors are commonly used in fine-chemical industries for the catalytic hydrogenation of organic substrates to a variety of products and intermediates (1-2). The most common types of catalysts are precious metals such as Pt and Pd supported on powdered carbon supports (3). The behavior of the gas-liquid-sluny reactors is affected by a complex interplay of multiple variables including the temperature, pressure, stirring rates, feed composition, etc. (1-2,4). Often these types of reactors are operated away from the optimal conditions due to the difficulty in identifying and optimizing the critical variables involved in the process. This not only leads to lost productivity but also increases the cost of down stream processing (purification), and pollution control (undesired by-products). 

Apart from reduced yield, down-stream processing can cause minor or even bigger modifications in the structure of the biomolecule. Often, these modifications do not affect the activity of the product, but may change its antigenicity. Along with virus safety, the reduction of such risks is a main objective in the down-stream processing of such biomolecules. Chromatographic purification,... 

Hoffman advises, Relying solely on a process-specific assay is ill advised and can result in failure to detect atypical process contaminants. In cases with a defined, persistent, and problematic host cell protein impurity, a down-stream process-specific assay may be justified. It is critical that the immunoassay be capable of detecting every possible host cell protein contaminant. 13... 

Down-stream processing, those steps in the process required for the isolation,... 

In the literature many examples of more or less exotic bioreactors can be found. Few actually are applied, outside the laboratory. Here two novel designs, the membrane and the liquid-impelled loop reactor, are discussed briefly. These two reactors are simple to use and, to a certain extent, liable to scale-up and both integrate the actual biocatalysis with part of the down-stream processing. 

Reif, O.W, and R. Ereitag, Comparison of membrane adsorber (MA) based purification schemes for the down-stream processing of recombinant h-AT III. Bioseparation, 1994. 4(6) 369-81. 

The third section deals with engineering principles of bioprocess. The chapter 8 deals with sterilization process and its engineering considerations (up stream process). The ninth chapter includes agitation and aeration in cellular growth and its impact on designing the bioreactors. The last chapter deals with brief introduction to down stream processing. 

Surface cleanliness is dominated by external contaminants such as airborne debris, scratches, etc. The size range of these contaminants is typically from submicron to tens of microns, both laterally and vertically. Polyester film is not manufactured under clean-room conditions and typically rolls of film are slit to size - dust is present or generated in these processes. These external contaminants are the major cause of surface related issues in down stream processing, but the bulk of these contaminants can be removed by some form of surface cleaning. 

No matter which method is selected for immobilization, two essential needs should be balanced, the catalytic needs (expressed as productivity, STY, stability and selectivity) and the noncatalytic needs (e.g., separation, control, down-streaming process) that are required by a given application. When both needs are satisfied, the immobilized enzyme can be labeled as robust [88]. 

Mattiasson, B., and Hakanson, H. (1991). Measurement and control in down-stream processing. In Measurement and Control in Bioprocessing (K. G. Carr-Brion, ed.), Chapter 8, pp. 221-250. Elsevier Applied Science. 

Developing molecularly imprinted polymers as receptors for recognising and binding proteins has practical applications (see also Chapter 10). Such polymers can be used as attractive materials for down stream processing of important... 

You have the choice of whether or not to operate an aseptic or non-aseptic system, and which down-stream processing operations to use. The costs of these operations are given below. 

Many factors play a role at this decision level. Type of kinetics, operational stability of the biocatalyst, form of biocatalyst, type of bioreactor, bioreactor operating costs, necessity of process control, compatibility with down-stream processing, tonnage or scale of operation, existing facilities and experience, feedstock, type of product, GMP, and others, are all involved in an intricate... 

Many operations—spills, emissions to the atmosphere, contamination of waste-water streams, and disposal of wastes—release solvents and other compounds to the environment. Controlling emissions is particularly important for continued operations on a manufacturing scale. To decrease emissions, reactions may be run at lower temperatures, or higher-boiling solvents may be chosen. Sometimes solvents are avoided if they are difficult to remove or if the chemist anticipates that the presence of this solvent will cause down-stream processing difficulties. DMSO can be considered one of these solvents Multiple extractions with HzO may be necessary to satisfactorily remove DMSO, and small amounts of residual DMSO may adversely affect the crystallization of the product. 

The creation of fine particles may be desired for specific down-stream processing or formulation requirements. Methods for control of these applications are also discussed in Section 10.5 below. 

Down-stream processing/unit operations (minimizing the number of stages necessary to obtain the product in the state desired by the customer). 

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