Recovery , enzyme unit operations

The principles and equipment discussed below are mostly focused on proteins and enzymes. Several other products, such as small molecules, metabolites, vitamins, and acids can require more specialized methods. However, many of the unit operations described here are also used in the recovery of these latter compounds. 

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. 

Stirred tanks are the chief kind of reactors for handling microorganisms or dissolved isolated enzymes, either as batch units or as continuous stirred tank batteries. When the enzymes are immobilized, a variety of reactor configurations is possible and continuous operation is easily implemented. The immobilization may be on granules or on sheets, and has the further advantage of making the enzymes reusable since recovery of dissolved enzymes rarely is feasible. 

Enzyme purification is aimed mainly to the removal of contaminant proteins therefore, enzyme purification is in essence a series of operations of protein fractionation. A compromise exists between purification and yield of recovery. Each operation intended for purification produces an increase in purity (conveniently expressed in terms of specific activity units of activity per unit mass of protein) but inevitably some enzyme activity is lost so that yield of recovery is lower than 100%. Purification factors and yields for a given operation (i) and global values for N consecutive operations are then ... 

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