14
J. Gomes and A.S. Menawat
Park et al. [32] have developed a FIA system for glucose, fructose, and sucrose.
They used a biosensor with permeabilized Zymomonas mobilis and invertase.
Cells of Zymomonas mobilis were permeabilized with toluene and co-immobilized with invertase within a porcine-skin gelatin membrane. The response time
of the FIA system is approximately 10 s. However, the actual implementation of
most biosensors in industrial processes have not been demonstrated. Although
a wide range of biosensors exist for measuring various biomolecules [33-36]
their direct successful applications are few. Restriction in autoclaving and
interference from components of complex medium formulations has discouraged a wider application of biosensors.
The wide scope of on-line and off-line measurements in process analysis,
monitoring and control has been reviewed pragmatically by Royce 1-37]. Although most of the process variables such as the pH, temperature, dissolved
oxygen, pressure, redox potential, gas and liquid flow rates, and power input are
routinely measured on-line, they provide only a segment of the total information
required to characterize the state of the bioreactor. With the exception of
dissolved oxygen, these measurements give little or no direct insight into the
physiological state of the process. For example, the cell mass (cell number or
viability), substrate and the product concentration, which give a better understanding of the physiological state of the process are usually measured off-line.
It is possible to relate the off-gas measurements to the physiological state of
the process. Consequently, off-gas is measured routinely for monitoring growth,
especially in aerated bioreactors. Off-gas can be measured using gas chromatography although it takes upto 10-30 min to complete an analysis by this
method. This restricts the use of gas chromatography in on-line optimization
and control. More commonly, oxygen and carbon dioxide are measured by
paramagnetic and infrared analyzers, respectively. The major problem with an
infrared carbon dioxide analyzer is its non specificity. It suffers from interference
from other compounds having similar radiation absorption characteristics,
especially water. Hence, elaborate arrangements are necessary to remove moisture from the sample. Paramagnetic oxygen analyzers are extremely sensitive to
pressure, flow rate and temperature, so that precision accessories are required to
maintain temperature and control the gas flow rate. However, since these
analyzers require only 5 s or less to complete an analysis and are accurate up to
2% or better, they are more suited than gas chromatography (GC) for on-line
implementations.
Mass spectrometry has been widely used in bioprocess monitoring and
control, and the cost is affordable then it is the method of choice. Mass
spectrometers are capable of making rapid and accurate estimates of multiple
species in bioreactor off-gas with linear response ranging over several orders of
magnitude. Recently, due to considerable improvement in analysis techniques,
there has been a resurgence in its application in bioprocess monitoring and
control [38]. Mass spectrometry in combination with separation techniques
such as high pressure liquid chromatography (HPLC) and capillary electrophoresis has opened a new front in biomolecule analysis. Mass spectrometers
J. Gomes and A.S. Menawat
Park et al. [32] have developed a FIA system for glucose, fructose, and sucrose.
They used a biosensor with permeabilized Zymomonas mobilis and invertase.
Cells of Zymomonas mobilis were permeabilized with toluene and co-immobilized with invertase within a porcine-skin gelatin membrane. The response time
of the FIA system is approximately 10 s. However, the actual implementation of
most biosensors in industrial processes have not been demonstrated. Although
a wide range of biosensors exist for measuring various biomolecules [33-36]
their direct successful applications are few. Restriction in autoclaving and
interference from components of complex medium formulations has discouraged a wider application of biosensors.
The wide scope of on-line and off-line measurements in process analysis,
monitoring and control has been reviewed pragmatically by Royce 1-37]. Although most of the process variables such as the pH, temperature, dissolved
oxygen, pressure, redox potential, gas and liquid flow rates, and power input are
routinely measured on-line, they provide only a segment of the total information
required to characterize the state of the bioreactor. With the exception of
dissolved oxygen, these measurements give little or no direct insight into the
physiological state of the process. For example, the cell mass (cell number or
viability), substrate and the product concentration, which give a better understanding of the physiological state of the process are usually measured off-line.
It is possible to relate the off-gas measurements to the physiological state of
the process. Consequently, off-gas is measured routinely for monitoring growth,
especially in aerated bioreactors. Off-gas can be measured using gas chromatography although it takes upto 10-30 min to complete an analysis by this
method. This restricts the use of gas chromatography in on-line optimization
and control. More commonly, oxygen and carbon dioxide are measured by
paramagnetic and infrared analyzers, respectively. The major problem with an
infrared carbon dioxide analyzer is its non specificity. It suffers from interference
from other compounds having similar radiation absorption characteristics,
especially water. Hence, elaborate arrangements are necessary to remove moisture from the sample. Paramagnetic oxygen analyzers are extremely sensitive to
pressure, flow rate and temperature, so that precision accessories are required to
maintain temperature and control the gas flow rate. However, since these
analyzers require only 5 s or less to complete an analysis and are accurate up to
2% or better, they are more suited than gas chromatography (GC) for on-line
implementations.
Mass spectrometry has been widely used in bioprocess monitoring and
control, and the cost is affordable then it is the method of choice. Mass
spectrometers are capable of making rapid and accurate estimates of multiple
species in bioreactor off-gas with linear response ranging over several orders of
magnitude. Recently, due to considerable improvement in analysis techniques,
there has been a resurgence in its application in bioprocess monitoring and
control [38]. Mass spectrometry in combination with separation techniques
such as high pressure liquid chromatography (HPLC) and capillary electrophoresis has opened a new front in biomolecule analysis. Mass spectrometers