Downstream process , enzymes

Biocatalysts in nature tend to be optimized to perform best in aqueous environments, at neutral pH, temperatures below 40 °C, and at low osmotic pressure. These conditions are sometimes in conflict with the need of the chemist or process engineer to optimize a reaction with respect to space-time yield or high product concentration in order to facilitate downstream processing. Furthermore, enzymes and whole cells are often inhibited by products or substrates. This might be overcome by the use of continuously operated stirred tank reactors, fed-batch reactors, or reactors with in situ product removal [14, 15]. The addition of organic solvents to increase the solubility of substrates and/or products is a common practice [16]. 

In downstream processing of a fermentation unit for enzyme production with a feed stream of sugar- at a concentration of 35 g-l the expected product to be recovered is a-amylase. 

The susceptibility of biological systems, including procaryotic and eucaryo-tic cultures and enzyme solutions, to the forces prevailing under normal processing conditions has been extensively studied and is the subject of comprehensive reviews [12-16], including other chapters in this volume. Downstream processing operations, as well as routine pumping, will expose cell suspensions... 

Downstream Processing Microfiltration plays a significant role in downstream processing of fermentation products in the pharmaceutical and bioprocessing industry. Examples are clarification of fermentation broths, sterile filtration, cell recycle in continuous fermentation, harvesting mammahan cells, cell washing, mycelia recovery, lysate recovery, enzyme purification, vaccines, and so forth. 

Whole-cell biotransformations frequently showed insufficient stereoselectivities and/or undesired side reactions because of competing enzymatic activities present in the cells. These side reactions can modify the substrates and/or products. Furthermore, whole-cell biotransformations are limited due to the intrinsic need to grow biomass, which generates its own metabolites that are not related to the biotransformation reactions and, therefore, which need to be removed during the downstream process. Both the cells themselves and the unrelated metabolites produced are impurities that need to be removed after the biotransformation reaction. With isolated enzymes, there are no organism and unrelated metabolites to remove after the biotransformation processes. 

As part of a downstream processing sequence, 10 m3 of a process fluid containing 20 kg m 3 of an enzyme is to be concentrated to 200 kg/m3 by means of ultrafiltration. Tests have shown that the enzyme is completely retained by a 10,000 MWCO surface-modified polysulphone membrane with a filtration flux given by ... 

In the development of cell or enzyme-based processes, many process configurations exist, including batch, fed batch and continuous operation. In general, the conversion and the separation processes (downstream processing) are regarded as separate units, and most industrial processes are based on this approach. In the last decades, however, more attention is paid to the integration of conversion and separation, leading to the development of membrane bioreactors [49, 50], and some of these concepts have reached an industrial scale. The membranes used for this type of reactors are almost exclusively polymeric, as temperatures seldomly exceed 100 °C for obvious reasons. 

The use of both hydrophilic [85, 87] and hydrophobic [84, 86] membranes has proven to be efficient in binding the enzyme. The main advantage of this system over emulsion systems lies in the ease of the downstream processing, as no enzyme-stabilized emulsion has to be broken. 

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. 

Reverse Micellar Extraction for Downstream Processing of Proteins/Enzymes... 

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