Enzymes - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 367

scheme varies depending on whether the enzyme is intracellular or extracellular. In some
cases, it may be more advantageous to use inactive (dead or resting) cells with the desired
enzyme activity in immobilized form. This approach eliminates costly enzyme separation
and purification steps and is therefore economically more feasible. Details of protein separa-
tions are covered later in the text.
The first step in the large-scale production of enzymes is to cultivate the organisms
producing the desired enzyme. Enzyme production can be regulated and fermentation
conditions can be optimized for overproduction of the enzyme. Proteases are produced by
using overproducing strains of Bacillus, Aspergillus, Rhizopus,andMucor; pectinases are
produced by Aspergillus niger; lactases are produced by yeast and Aspergillus; lipases are
produced by certain strains of yeasts and fungi; and glucose isomerase is produced by Fla-
vobacterium arborescens or Bacillus coagulans. After the cultivation step, cells are separated
from the media usually by filtration or sometimes by centrifugation. Depending on the intra-
cellular or extracellular nature of the enzyme, either the cells or the fermentation broth is
further processed to separate and purify the enzyme. The recovery of intracellular enzymes
is more complicated and involves the disruption of cells and removal of cell debris and
nucleic acids. Figure 8.18 depicts a schematic of an enzyme plant producing extracellular
enzymes.
In some cases, enzyme may be both intracellular and extracellular, which requires process-
ing of both broth and cells. Intracellular enzymes may be released by increasing the perme-
ability of cell membrane. Certain salts such as CaCl 2 and other chemicals such as

Precipitation
i ntial

fracti onal

Medium Tank

Waste biomass

Seed
Fermenter

Fermenter
Tanks

Surge Tank
at 4

Debris
removal C

Cold water

Heat exchanger

Precipitate
separation

Buffer

Storage

Concentrate

Dialysis

Ultrafiltration

Vacuum

Packing

Waste

Fractional collection

Freeze
drier

FIGURE 8.18 A flowsheet for the production of an extracellular enzyme.