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Preface
The biotechnology and chemical engineering students at various
Indian Universities and engineering institutions are required to take
up the 'Biochemical Engineering' course either as an elective or a
compulsory subject. This book is written keeping in mind the need
for a text book on the aforesaid subject for students from both
engineering and biology backgrounds. The main feature of· this book
is that it contains s'olved problems, which help the students to
understand the subject better.
The book is divided into three sections: Enzyme mediated
bioprocess, whole cell mediated bioprocess and the engineering
principle in bioprocess
In the first section of this book, the brief introduction about
biochemical engineering is given in chapter 1. The second chapter
deals with basics of enzyme reaction kinetics. The third chapter deals
with an important aspect in enzyme bioprocess Le. immobilization of
enzyme and its kinetics. Chapter 4 is concerned about the industrial
bioprocess involving starch and cellulose.
The second section of this book is related to whole cell mediated
bioprocess. Chapter 5 introduces students with basics of
microbiology and cell culture techniques for both plant and animal
cells. The area emerged as most important because of latest
development in pharmaceutical industry. Chapter 6 deals with cell
kinetics and fermenter design. The kinetics analysis based on
structure and unstructured model is also included. In chapter 7,
genetic engineering aspects were explained, and genetic stability
problems and important engineering aspects of genetically modified
cells were also addressed.
The third section deals with engineering principles of bioprocess.
The chapter 8 deals with sterilization process and its engineering
considerations (up stream process). The ninth chapter includes
agitation and aeration in cellular growth and its impact on designing
the bioreactors. The last chapter deals with brief introduction to
down stream processing.
Introduction
Biochemical engineering is concerned with conducting biological
processes on an industrial scale. This area links biological sciences
with chemical engineering. The role of biochemical engineers has
become more important in recent years due to the dramatic
developments of biotechnology.
1.1 BIOTECHNOLOGY
Biotechnology can be broadly defined as "Commercial techniques
that use living organisms, or substances from those organisms, to
make or modify a product, including techniques used for the
improvement of the characteristics of economically important plants
and animals and for the development of microorganisms to act on the
environment ... " (Congress of the United States, 1984). If
biotechnology is defined in this general sense, the area cannot be
considered new. Since ancient days, people knew how to utilize
microorganisms to ferment beverage and food, though they did not
know what was responsible for those biological changes. People also
knew how to crossbreed plants and animals for better yields. In
recent years, the term biotechnology is being used to refer to novel
techniques such as recombinant DNA and cell fusion.
Recombinant DNA allows the direct manipulation of genetic
material of individual cells, which may be used to develop
microorganisms that produce new products as well as useful
organisms. The laboratory technology for the genetic manipulation
within living cells is also known as genetic engineering. A major
objective of this technique is to splice a foreign gene for a desired
product into circular forms of DNA (plasmids), and then to insert
them into an organism, so that the foreign gene can be expressed to
produce the product from the organism.
Cell fusion is a process to form a single hybrid cell with nuclei and
cytoplasm from two different types of cells in order to combine the
desirable characteristics of the two. As an example, specialized cells
of the immune system can produce useful antibodies. However, it is
difficult to cultivate those cells because their growth rate is very slow.
2 Fundamentals ofBiochemical Engineering
On the other hand, certain tumor cells have the traits for immortality
and rapid proliferation. By combining the two cells by fusion, a
hybridoma can be created that has both traits. The monoclonal
antibodies (MAbs) produced from the hybridoma cells can be used
for diagnosis, disease treatment, and protein purification.
The applications of this new biotechnology are numerous, as listed
in Table 1.1. Previously expensive and rare pharmaceuticals such as
insulin for diabetics, human growth hormone to treat children with
dwarfism, interferon to fight infection, vaccines to prevent diseases,
and monoclonal antibody for diagnostics can be produced from
genetically modified cells or hybridoma cells inexpensively and also
in large quantities. Disease-free seed stocks or healthier, higheryielding
food animals can be developed. Important crop species can
be modified to have traits that can resist stress, herbicide, and pest.
Furthermore, recombinant DNA technology can be applied to
develop genetically modified microorganisms so that they can
produce various chemical compounds with higher yields than
unmodified microorganisms can.
1.2 BIOCHEMICAL ENGINEERING
The recombinant DNA or cell fusion technologies have been initiated
and developed by pure scientists, whose end results can be the
development of a new breed of cells in minute quantities that can
produce a product. Successful commercialization of this process
requires the development of a large-scale process that is
technologically viable and economically efficient. To scale up a
laboratory-scale operation into a large industrial process, we cannot
just make the vessel bigger. For example, in a laboratory scale of 100
mL, a small Erlenmeyer flask on a shaker can be an excellent way to
cultivate cells, but for a large-scale operation of 2,000 L, we cannot
make the vessel bigger and shake it. We need to design an effective
bioreactor to cultivate the cells in the most optimum conditions.
Therefore, biochemical engineering is one of the major areas in
biotechnology important to its commercialization.
To illustrate the role of a biochemical engineer, let's look at a
typical biological process (bioprocess) involving microbial cells as
shown in Figure 1.1. Raw materials, usually biomass, are treated and
mixed with other ingredients that are required for cells to grow well.
The liquid mixture, the medium, is sterilized to eliminate ·all other
living microorganisms and introduced to a large cylindrical vessel,
bioreactpr or fermenter, typically equipped with agitators, baffles, air
spargers, and various sensing devices for the control of fermentation
conditions. A pure strain of microorganisms is introduced into the
vessel. The number of cells will start to multiply exponentially after a
Introduction 3
certain period of lag time and reach a maximum cell concentration as
the medium is depleted. The fermentation will be stopped and the
contents will be pumped out for the product recovery and
purification. This process can be operated either by batch or
continuously
BIOLOGICAL PROCESS
Industrial applications of biological processes are to use living cells
or their components to effect desired physical or chemical changes.
Biological processes have advantages and disadvantages over
traditional chemical processes. The major advantages are as follows:
1. Mild reaction condition: The reaction conditions for bioprocesses
are mild. The typical condition is at room temperature,
atmospheric pressure, and fairly neutral medium pH. As a
result, the operation is less hazardous, and the manufacturing
facilities are less complex compared to typical chemical
processes.
2. Specificity: An enzyme catalyst is highly specific and catalyzes
only one or a small number of chemical reactions. A great
variety of enzymes exist that can catalyze a very wide range of
reactions.
6 Fundamentals ofBiochemical Engineering
3. Effectiveness: The rate of an enzyme-catalyzed reaction is
usually much faster than that of the same reaction when
directed by nonbiological catalysts. A small amount of enzyme
is required to produce the desired effect.
4. Renewable resources: The major raw material for bioprocesses is
biomass which provides both the carbon skeletons and the
energy required for synthesis for organic chemical
manufacture.
5. Recombinant DNA technology: The development of the
recombinant DNA technology promises enormous possibilities
to improve biological processes.
However, biological processes have the following disadvantages:
1. Complex product mixtures: In cases of cell cultivation (microbial,
animal, or plant), multiple enzyme reactions are occurring in
sequence or in parallel, the final product mixture contains cell
mass, many metabolic by-products, and a remnant of the
original nutrients. The cell mass also contains various cell
components.
2. Dilute aqueous environments: The components of commercial
interests are only produced in small amounts in an aqueous
medium. Therefore, separation is very expensive. Since
products of bioprocesses are frequently heat sensitive,
traditional separation techniques cannot be employed.
Therefore, novel separation techniques that have been
developed for analytical purposes, need to be scaled up.
3. Contamination: The fermenter system can be easily
contaminated, since many environmental bacteria and molds
grow well in most media. The problem becomes more difficult
with the cultivation of plant or animal cells because their
growth rates are much slower than those of environmental
bacteria or molds.
4. Variability: Cells tend to mutate due to the changing
environment and may lose some characteristics vital for the
success of process. Enzymes are comparatively sensitive or
unstable molecules and require care in their use.
1.4 DEFINITION OF FERMENTATION
Traditionally, fermentation was defined as the process for the
production of alcohol or lactic acid from glucose (C6H120 6).
Yeast)
enzymes 2CH3CHOHCOOH
Introduction 7
A broader definition of fermentation is "an enzymatically
controlled transformation of an organic compound" according to
Webster's New College Dictionary (A Merriam-Webster, 1977) that we
adopt in this text.
1.5 PROBLEMS
1.1 Read anyone article as a general introduction to
biotechnology. Bring a copy of the article and be ready to
discuss or explain it during class.
1.6 REFERENCES
Congress of the United States, Commercial Biotechnology: An International
Analysis, p. 589. Washington, DC: Office of Technology Assessment, 1984.
Journals covering general areas of biotechnology and bioprocesses:
Applied & Environmental Microbiology
Applied Microbiology and Biotechnology
Biotechnology and Bioengineering
CRC Critical Review in Biotechnology
Developments in Industrial Microbiology
Enzyme andMicrobial Technology
Journal ofApplied Chemistry & BiotechnoLo(~y
Journal of Chemical Technology & Biotechnolog,ll
Nature
Nature Biotechnology
Science
Scientific American