Bioproducts cell separation

Membranes are particularly suited for bioprocesses involving the cultivation of microorganisms or cells as biocatalysts, in which the product of interest is produced extracellularly. Such processes are becoming increasingly attractive when compared to those in which the products accumulate intracellularly. Some of the reasons for this include the use of novel expression systems which favor higher product concentrations, and the ease of purification as compared to an intracellular bioproduct route. One of the drawbacks remains that extracellular protein products are produced in dilute concentration. Extracellular-product based-processes require cell separation, product recovery and concentration. The use of ultrafiltration and microfiltration membranes has become a method of choice in such process schemes. 

The separation of cells from the culture media or fermentation broth is the first step in a bioproduct recovery sequence. Whereas centrifugation is common for recombinant bacterial cells (see Centrifugal separation), the final removal of CHO cells utilizes sterile-filtration techniques. Safety concerns with respect to contamination of the product with CHO cells were addressed by confirming the absence of cells in the product, and their relative noninfectivity with respect to immune competent rodents injected with a large number of CHO cells. 

Bioproducts are usually secreted from animal cells in culture, and can be purified after cell removal by solid-liquid separation techniques (see Chapter 11). However, the product can sometimes be found within the cell and this requires its extraction from the cellular mass, which contains numerous molecular species that can have high viscosity and proteolytic activity, which increases the difficulty of sample handling. 

Some bioproducts are derived from fermentation by living organisms but immobilized enzymes can also catalyze a biotransformation. If the product is extracellular, then the initial steps of recovery include removal of the cells and other particulate matters from the broth. If the product is intracellular, it would be necessary to lyse the cells to release the product into the broth. The cell debris is then separated before the product is recovered from the broth. In certain cases, proteins produced as IBs need to be solubilized and the proteins renatured before further recovery steps. In the case of biotransformed products, the immobilized cells or enzymes and their support need to be removed initially. 

A Fuzzy Expert System for Separation Sequencing of Bioproducts Computer Aided Modeling of Bacteria Cells The Use of Expert Systems... 

This book covers several of the emerging areas of separations in biotechnology and is not intended to be a comprehensive handbook. It includes recent advances and latest developments in techniques and operations used for bioproduct recovery in biotechnology and applied to fermentation systems as well as mathematical analysis and modeling of such operations. The topics have been arranged in three sections beginning with product release from the cell and recovery from the bioreactor. This section is followed by one on broader separation and concentration processes, and the final section is on purification operations. The operations covered in these last two sections can be used at a number of different stages in the downstream process. 

The immobilization of whole cells provides a means for the entrapment of multistep and cooperative enzyme system present in the intact cell, repetitive use and improved stabihty. This technique is also advantageous in the separation of bioproducts from cell mass in a continuous bioconversion process [114,115]. The other advantages of immobilized growing cells include (1) protection of cells against unfavourable environmental factors (2) changes in the permeability of the cells (3) reduced inhibition by substrate and product (4) reusability and (5) faster removal of end product. 

Tubular bowl centrifuges are routinely used in smaller-scale separations of suspended material from fermentation beer. The objective may be to recover the cells which are to be disrupted to recover intracellular bioproducts. Alternatively, for extracellular bioproducts, the beer hcis to be clarified (be free of cells, cellular debris, etc.). Table 7.3.1 provides the dimensions and/or densities of a few types of microorganisms/cells/particles. Two special features of the separation of the suspensions in fermentation beer as feed are their very low density difference (pp-Pi) and smaller particle sizes. In the separation of suspended materials from the fluid in nonbiological systems, (pp -pf) is considerably larger. Further, the particle dimensions have wide variations. 

---