Conventional downstream processing

Fig. 17.1. Conventional downstream processing scheme for the purification of proteins.

Downstream process for the purification of surfactin includes acidifying the culture supernatant followed by filtration. Neutralization of the trapped liquid with alkaline solution results in formation of product, sodium surfactin after evaporation. Conventional downstream process, which uses organic solvent has been dropped now by the industries due to environmental and cost concerns. 

One of the most important advantages of the bio-based processes is operation under mild conditions however, this also poses a problem for its integration into conventional refining processes. Another issue is raised by the water solubility of the biocatalysts and the biocatalyst miscibility in oil. The development of new reactor designs, product or by-product recovery schemes and oil-water separation systems is, therefore, quite important in enabling commercialization. Emulsification is thus a necessary step in the process however, it should be noted that highly emulsified oil can pose significant downstream separation problems. 

The growing interest in various )5-lactam antibiotics, especially the cephalosporins, over the last decade has called upon improvement in their production methods via modification of either the basic process and the microbial strain or the downstream processing techniques. The product recovery may involve various methods of extraction and purification which play an important role in the overall process economics [12]. During recent years much attention has been given to the development of liquid membrane (LM) processes which usually exhibit high extraction rates and selectivity as compared to those achievable in conventional solvent extraction and adsorption processes. 

Production of polymers contributes to pollution during synthesis and after use. A polymer produced by microorganisms is already a commercial product (Biopol). Unfortunately, however, cellular synthesis remains limited by the cost of downstream processing and the fact that the synthesis is aqueous-based, and it is impossible to perform the synthesis in the absence of a solvent. Recent research describes an enzyme-catalyzed polymer synthesis in which there is no solvent. This bulk polymerization mirrors conventional synthesis but eliminates the needs for extremes of temperature and corrosive acid catalysts. This represents the first rapid and efficient synthesis of polyesters from bulk polymerization under ambient conditions with very low concentrations of a biocatalyst (Chaudhary et al., 1997). 

As the ligand-protein interaction takes place at the internal surface of porous adsorbents, kinetics and equilibrium of the interaction should be independent of the interstitial voidage within an adsorbent bed. Therefore the equilibrium capacity of an adsorbent will not be influenced by different experimental configurations e.g. batch stirred tank, batch fluidized bed, frontal application to packed or fluidized beds. The major difference arises from the medium from which the protein is isolated. As fluidized beds are used for whole broth adsorption, the properties of the broth have to be considered regarding the possible influence of components which are removed in conventional primary recovery steps and therefore are not present during the initial chromatography operations in a standard downstream process. These are on one hand nucleic... 

The conventional production consisted of many process steps, typical for a fine chemical process. These process steps are given in Figure 6. The selectivity of the enzyme is rather high. The downstream processing is rather laborious,... 

The article is directed mainly at conventional caustic refining and related downstream processes with related considerations in physical refining and new... 

The water separated in the demulsification step is similar in character to water produced in a conventional refinery desalting process. Although no detrimental effects are anticipated, the impacts of surfactants in the water or downstream processing units must be evaluated for each specific case. The water phase may contain surfactant fragments that could require treatment or removal prior to disposal. Refineries, however, use a variety of chemicals, catalysts, additives, etc., many of which end up in waste streams and require treatment. 

The steps followed in downstream processing of rhGDNF expressed in E. coli are very similar to any conventional method used to purify target proteins expressed as IBs in bacteria. However, the specific reagents used at different stages are decided after optimization at a lower scale. Alternative methods exist to... 

Biological production of lactic acid is complicated primarily due to economical considerations arising from product inhibition and the required downstream processing of dilute aqueous product streams. The standard method of biological lactic acid production is the anaerobic fermentation by Lactobacillus in a batch reactor [7]. The conventional process requires the base to be added to the reactor to control the pH and the use of calcium carbonate to precipitate the lactate. This process produces a lactate salt that must be acidified (usually by sulfuric acid) to recover the lactic acid, with calcium sulfate as an undesirable by-product. 

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