Bioseparations product isolation

Citric acid and vitamin C are examples of very large scale fermentation processes where the subsequent product isolation involves several bioseparations, including filtration, precipitation, evaporation, crystallization, and drying methods. The scale of operation requires careful choice of equipment which is robust, efficient in separating product from unwanted by-products, and cost effective to be competitive. 

Techniques used in bioseparations depend on the nature of the product (i.e., the unique properties and characteristics which provide a handle for the separation), and on its state (i.e., whether soluble or insoluble, intra- or extracellular, etc.). All early isolation and recovery steps remove whole cells, cellular debris, suspended solids, and colloidal particles, concentrate the product, and, in many cases, achieve some degree of purification, all the while maintaining high yield. For intracellular compounds, the initial harvesting of the cells is important... 

The development of genetically engineered plants offers the prospect of pharmaceutical production from crops as well as improved yields for cereals, vegetables and other agricultural products. The challenge will then be to find suitable bioseparations to enable the efficient isolation of such products. 

After biomass removal has been achieved if appropriate, the main objective of the primary recovery stages is to isolate the product from significant impurities which will generally be in the same phase. At this stage of bioseparation, it is necessary to exploit some difference between the product and impurities such as solubility (in water or an organic solvent), particle size, surface affinity, charge and so on. 

Cell disruption techniques are used to recover materials produced within the cell, for example, industrial enzymes and some pharmaceutical proteins. Generally this stage of bioseparation will follow cell recovery, for example, by centrifugation, and precede the isolation of the desired product from the cell debris which is also produced during the disruption process. 

A holistic approach to the selection of bioseparation equipment is vital, so that the unit operation is not considered in isolation, but in relation to the whole process, the facility or site where it will be located, the nature of the product, and the operating and capital costs. Only then can an informed decision be made to find the right balance between product quality and yield, processing costs and capital investment. 

The initial emphasis in analytical biotechnology was on broad safety concerns that translated into detection of host-cell components such as DNA, endotoxins, Escherichia colt proteins, and retroviral contamination.2 The detection of these impurities requires development of high-sensitivity assays that are based primarily on antibodies [e.g., enzyme-linked immunosorbent assay (ELISA) for E. coli proteins) or radioactivity (e.g., dot-blot assays for DNA detection). New developments are focused on low-sensitivity detection, characterization, and removal of undesirable target sequence variants. Bioseparations play an important role even after a product has been isolated and shown to contain a low level of contaminants for initiation of clinical studies. The focus shifts to achievement of a reproducible, large-scale manufacturing process. At this stage, analytical methods provide essential informa-... 

The aim of this book is not to provide an exhaustive treatise on all areas of isolation and purification of biotechnology products, but to present the spectrum of current thinking and activities on bioseparations, specifically of large molecules such as proteins and polysaccharides. The chapters are divided into three categories extraction and membrane processes, processes using biospedfic interaction with proteins, and novel isolation and purification processes. 

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