Cell bead mills/high-pressure homogenizer

Recovery. The principal purpose of recovery is to remove nonproteinaceous material from the enzyme preparation. Enzyme yields vary, sometimes exceeding 75%. Most industrial enzymes are secreted by a microorganism, and the first recovery step is often the removal of whole cells and other particulate matter (19) by centrifugation (20) or filtration (21). In the case of ceU-bound enzymes, the harvested cells can be used as is or dismpted by physical (eg, bead mills, high pressure homogenizer) and/or chemical (eg, solvent, detergent, lysozyme [9001 -63-2] or other lytic enzyme) techniques (22). Enzymes can be extracted from dismpted microbial cells, and ground animal (trypsin) or plant (papain) material by dilute salt solutions or aqueous two-phase systems (23). 

Cell disruption Bead mills High-pressure homogenization Ultrasonication... 

Intracellular Products. Intracellular production of bioproducts is less preferable but sometimes the only way to produce certain compounds in appreciable amounts. In this case, cell disruption is required for recovery. High-pressure homogenization, bead mills, and chemical or enzymatic disruption of the cell wall with lysozyme or similar enzymes can be used to achieve cell breakage. In the case of small molecules, organic solvent extraction has also been described. If cell debris remains in the centrate, it must be removed by methods described above, thus adding extra steps to the process. 

If the value product occurs intracellularly, the slurry is taken up in washing buffers of appropriate ionic strength for preparation of the cell rupture, which occurs, e.g., by high-pressure homogenization, sonification, bead milling, or eny-matic procedures. 

Since most industrial enzymes are produced extracellularly, only unit operations used for recovering these types of enzymes are considered. For intracellularly produced enzymes, additional steps must be included to harvest and open the cells (e.g., by a bead mill or high-pressure homogenizer). This complicates the process and increases the costs hence this type of processing is avoided, if possible. A recovery process typically consists of a pretreatment, followed by a primary separation of the enzyme from the biomass. Later, the enzyme is concentrated by removal of water, and unwanted impurities are removed in a purification step. Figure 27.4 illustrates an example of a simplified recovery process. 

Liquid shearing, such as high pressure homogenization, solid shear, such as bead milling and the extrusion of frozen cells are the most common mechanical methods for cell disruption (D souza and Killedar, 2008 Hatti-Kaul and Mattiasson, 2003). These methods are mainly based on the use of mechanical force to disrupt the cell. Some of these techniques, such as bead milling, have already found applications on a large scale (Prasad, 2010). 

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