Downstream Operations in Bioprocesses

It should be pointed out here that most biochemical separation methods that have been developed in research laboratories cannot necessarily be practiced on an industrial scale, so as to achieve high recovery levels. Rather, innovative approaches are often necessary in these industrial processes to achieve separations that ensure high purity and good recovery of the target product. 

Biochemical Engineering A Te xthookfor Engineers, Chemists and Biologists, Second Edition. 

Shigeo Katoh, Jun-ichi Horiuchi, and Fumitake Yoshida. 

Ion-exchange chromatography Hydrophobic Interaction chromatography Affinity chromatography 

The interferon is produced within the E. coli cells, which must first be separated from the culture media by using centrifugation. The isolated cells are then solubilized by cell disruption, after which the fraction containing interferon is concentrated by salting-out. Two subsequent procedures using immunoaffinity and cation-exchange chromatography raise the purity of the interferon 1000-fold. 

Biochemical Engineering A Textbook for Engineers, Chemists and Biologists Shigeo Katoh and Fumitake Yoshida 

Copyright 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-32536-8 

Cell disruption Bead mills High-pressure homogenization Ultrasonication 

Precipitation Ultrafiltration Aqueous two-phase separation Salting-out Isoelectric precipitation Organic solvent 

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In the downstream processing of bioprocesses, fixed-bed adsorbers are used extensively both for the recovery of a target and for the removal of contaminants. Moreover, their performance can be estimated from the breakthrough curve, as stated in Chapter 11. The break time tg is given by Equation 11.13, and the extent of the adsorption capacity of the fixed bed utilized at the break point and loss of adsorbate can be calculated from the break time and the adsorption equilibrium. Affinity chromatography, as weii as some ion-exchange chromatography, are operated as specific adsorption and desorption steps, and the overall performance is affected by the column capacity available at the break point and the total operation time. 

Most phannaceutical substances are manufactured in batch processes by (a) chemical synthesis, (b) fermentation, (c) isolation and recovery from natural sources, and (d) a combination of the above. Fermentation broths are usually very dilute and contain many complex compounds as given in Table 3.3 [23]. Because of the dilute and impure nature of the broths and sensitivity to operating conditions, MF, UF and NF are weU-suited for downstream processing, i.e., separation, isolation, purification and recovery of the product. Several membrane applications in bioprocessing are illustrated in Figure 3.24 [23] including gas separation (GS). 

When planning an industrial-scale bioprocess, the main requirement is to scale up each of the process steps. As the principles of the unit operations used in these downstream processes have been outlined in previous chapters, at this point we discuss only examples of practical applications and scaling-up methods of two unit operations that are frequently used in downstream processes (i) cell separation by filtration and microfiltration and (ii) chromatography for fine purification of the target products. 

One essential part of downstream processing is the movement of fermenter broths, supernatant fluids and whole cell slurries around the production plant. In the pharmaceutical industry, this has been traditionally achieved by pressure or gravity feed. In general, these methods are slow and unsuitable for large scale and continuous bioprocesses. The use of pumps is now the preferred method for most fluid transfer operations. 

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