Good morning students. The topic of today’s discussion is Manufacture of biochemicals.
Now, in our earlier classes, we have already learnt about the cells and we have also learnt
that, cells are of two types; one is the prokaryotic and another is the eukaryotic. So, we have
also learnt that, how eukaryotic cells are different from that of the prokaryotic cells.
We have also learnt that, prokaryotic cells are the primitive cells and eukaryotic cells
are the advanced, or the modern cells, where all these organelles are performing different
activities. And, when we have studied the cells and its organelles, we have also learnt
that, how each and every organelles are participating in different activities of the cell.
Now, then, in some other classes, we have also learnt that, how the metabolic reactions
are going on within the cell. And, we have also seen that, how this manipulation of cells,
that means, that incorporation of one particular gene, can be inserted to another particular
organism and with proper expression, how we can go for the over-production of any metabolites
which can be produced in the cell. Now, today, in our, this particular class, we will be
learning that, how this biochemicals can be manufactured and what are the different techniques
and how one can produce this biochemicals for different activities, different applications.
Now, here, coming to this biochemicals, if we are, if we see this biochemicals, then,
we can find that, the cell itself can be used as a biomass and this biomass can be used
for different purposes. And, the microorganism, with its own metabolites which is produced
within the cell, or which are produced within the cell, can be referred as the product of
our own interest, from the natural, or genetically improved strains.
Now, here, in my earlier classes, I have all ready mentioned you that, in the prokaryotic
cell, particularly in bacteria, there is a plasmid DNA. Now, if we remember that, what
is that plasmid? Plasmid is a circular double helix structured DNA and it can be, with the
restriction enzymes, we can make it a linear DNA; we can insert our targeted gene to this
and once again, with the another enzyme called ligase, we can once again express this particular,
this plasmid DNA, to any expression system; it maybe a bacteria, it maybe any higher organism,
eukaryotic cell, yeast, or fungi, or anything. So, if we see, and, why we are doing this
type of genetically engineered organism? We are doing this type of genetically engineered
organism, because of the over production, or improved productivity. Now, this products,
products what I am talking about today, maybe amino acids, it maybe antibacterial agent,
it maybe antifungal agent, it maybe carbohydrates, it maybe dyes and cosmetics ingredient, it
maybe enzymes, foods, and so on; it can be that lipid, it can be the nucleotide, and
its precursors; it can be organic synthesis and its intermediates, pharmaceutical significant
compound, it maybe plant growth factors, steroid, toxins, vitamins, coenzymes, and so on. So,
any metabolite which can be produced in any living cells can be considered as the biochemicals.
Now, how we are going for such type of things? We can use some lower group of microorganisms,
what we have learned the architecture and different organelles, and we have already
learnt that, how they behave and from that previous knowledge, we can now implement those
knowledge, basic knowledge, for application oriented work. Now, here, when we are just
talking about this particular insertion of one particular gene of our interest to any
primitive organism, and if we are over producing this, all this activities are coming under
the recombinant DNA technology, that is otherwise known as r DNA technology; or, we can tell
that, these are the genetically engineered strains. Now, this over production can be
done, either by genetically engineered strains, or sometimes, we can take the natural, or
the wild strains too, where such type of metabolic productions or productivities are there. So,
these types of strains can be used for human therapeutics; it can be used for enzymes;
it can be used for amino acids and so on. So, any metabolites which are biological in
nature, and produced by the cells, can be used for biochemical production.
At a glance, if we see the different types of biochemical products, then, we can classify
this, the different biochemicals, into different sectors, like that chemical sectors, pharmaceuticals,
energy, food, agriculture and so on. Now, if we further classify the chemicals under
each sector, then, we can find that, some of this chemicals like ethanol, acetone, butanol,
etcetera, that are used as a bulk chemicals; organic acids like acetic acid, butyric acid,
propionic acid, citric acids and so on; enzymes, polymers, and these are the product which
are coming under the chemical sectors, which can be produced from the biological origins
too. Pharmaceuticals such as antibiotics, enzyme,
enzyme inhibitor, monoclonal antibodies, steroids, vaccine, and so on, are coming under the pharmaceuticals,
or the health care sector. When we are talking about the energy sectors, then, we are mainly
talking about the ethanol that is, that is used as a gasohol and methane, that is the
biogas, which has got immense applications, immense importance, as far as today’s world
is concerned. Food is also another important sector, where we can consider any dairy products,
like cheese, yoghurts, any baker's yeast, beverages like beer, wine, food additives,
amino acid, vitamins, single cell proteins, etcetera, which are coming under the food
sector. When we are talking about the agriculture, then, animal feed, waste treatment process,
vaccine, microbial pesticide, herbicides, etcetera, mycorrhizal inoculants, etcetera,
these are the products which are very much coming under the agricultural sector.
So, here, I am just telling few names as a symbol that, any biological, or biochemicals,
which are produced in any particular cells, any particular living cell, can be considered
as the biochemicals, and we can go for the manufacture, or the production, or synthesis
of that particular product in living cell. Now, when we are talking about the cell, then,
obviously, I have told you, the cells are of different types, and depending upon the
development, we have categorized these cells into different sectors. One is the microbial
cell; another is the plant cell; another is the animal cell. Now, while talking to this
architecture and the cell organelles, I have also mentioned you that, animal cells are
different from the plant cells are the different from microbial cell. So, each and every cell,
irrespective of its origin, has certain similarities and certain differences; and those things,
we have already learned. Now, coming to the animal cell cultivation.
Now, when we are talking about the animal cell culture, then, we are just taking those
cells from the parent cell, or the donor cell. Now, when we are taking this, we are considering
the animal cell cultivation. The cells which are removed from the animal tissues can be
cultivated in nutritional medium outside of the donor’s body; that means, we are taking
those cells, and we are, we are making some environment in such a way, which will mimic
the body conditions; that means, whatever is the body conditions, that, whatever is
the physiological, pH, temperature, everything, we are simulating that, in any other environment
and we are making that environment suitable for this animal cell cultivation.
Now, this tissue culture methodology has given researchers the opportunity to study the cancer
cell, to classify malignant tumors, to determine tissues compatibility in transplantation,
and to study the specific cells and their interactions. So, when we are just going for
these, so, different types of techniques are there. One of the techniques is that, one
cell line, you just, normal cell line, you take, another cancerous cell line, you just
take; and, you fuse both the cells together, and the resultant product, what we are getting
is called the hybrid cell; that, one is the malignant, that cancerous, that malignant
cell, another is the, one is the tumorous, another is the normal and they are getting
fused and we are getting the hybridomas cell. Now, this is one type of cell cultivation.
There are very many types of cell cultivation. Now, why we are taking this cancerous cell
for such type of activities? One of the reason is that, we already learnt that, this cancer
cell has got one characteristics that, they do not have any control on its cell growth;
n number of multiplication and cell divisions are going on, resulting in the formation of
tumor. And, this particular characteristic, we would like to mimic, we would like to exploit
for our metabolite production; and this way, when we are going for this cell cultivation,
we can produce different types of biologicals, which can be synthesized through this technique.
One of the very important products is your human growth hormone, interferon, plasminogen
activators, viral vaccine, monoclonal antibodies and so on. These are some of the symbolic
products I, I am just showing you, just which has got immense applications, as far as human
health is concerned. Now, when, some mammalian gene products can
also produced by this bacterial system using the recombinant DNA technology. Now, what
we are doing? Now, mammalian cell culture, what we have seen? We have seen that, some
of the cells we are taking from the donor cell and then, we are simulating some environment
where it will mimic the body condition and cells will be proliferating; and this is the
animal cell cultivation. In other way, I told you, very many techniques are there; that
is one technique. Another technique is that, we can take the gene of our interest, which
is giving our targeted product and we are just splicing that gene from that mammal’s
body and we are inserting that gene to any bacteria. Now, here, say, as I have told,
this mammalian gene, can also get expressed in some microorganism, by taking some microbes,
we can express that particular gene which is coming under the recombinant DNA technology.
First, why, why we are going for such type of things, that mammalian gene, we are just
taking and we are just getting it expressed in the very lower group of organism? Because,
microorganisms can grow very fast. So, because of its fast growth rate and inexpensive medium
required for the bacterial cells, make them an economical alternative to the mammalian
cell culture. Now, just you imagine, if we are mimicking any body system, just see, how
costly that particular affair is, that condition will be. So, here, if we can take that gene
out of this mammal, and if we can insert that to any bacteria, and if we can express, we
can cultivate that particular bacteria for that particular product formation, then, what
will happen; then, the production cost, medium requirement and everything will be the bacterial
type; it is gene of mammal, but, that media, or the particular organism where we are expressing
that particular gene, is the microorganism. So, we can use that microbial media for the
microorganisms’ growth. So, it is very easy; it is very cheaper than that mimicking the
biological, that tissue or the body condition. So, we can produce a cost effective product
in this particular condition; however, bacteria lack the capability of post translational
modification, which involve proteolytic cleavage, subunit association, or a variety of additional
reactions, such as glycosylation, methylation, phosphorylation, acylation, and so on. These
modifications are important for proper biological activities of the product. Now, as in my earlier
classes, I have told you that, how simple a bacterial cell is and how complex the eukaryotic
cell is compared to this prokaryotic cell. Now, when we are taking some gene from a complex
system to a simplified system, simple media, simple system, and we are just expressing
that particular thing, it is happening that and we have also seen that, transcription,
translation and all those, that central dogma which is going on for protein synthesis and
entire body regulations, we have already learnt those things and now, we can understand that,
what is going on within the cell. Now, when such type of activities are going on after
translation, that process, when protein is being synthesized in higher organism, higher
cells, that post translational modifications are needed, are done, which is very much lacking
in the prokaryotic system; because in higher system, more organelles and more complexities
are there; more modifications, or updated reactions are going on, which is not there
in the bacterial system; and, that is the reason why, sometimes, after successful expression,
some problems we have to face, which is very much needed for proper biological activities
of that particular product. Therefore, an inactive polypeptide have been, had to be
isolated and refolded into proper structures of active proteins in-vitro, which can be
difficult and expensive procedures.
So, these are some of these problems and what are the actual problem associated with the
mammalian cell cultivation process is that, if we see that cell cultivation, if we compare
the mammalian cell with any microbial cell, we can find that, everything is different,
starting from its architecture, to its behavioral properties, everything is different. Now,
here, what we can see that, mammalian cells are larger and more complex than most of the
microorganisms. Their growth rate is very slow compared to the microorganism. Therefore,
the productivity is low and the maintenance of sterility is very, very difficult. This
is one of the very important points, as far as animal cell culture is concerned.
Now, as they are growing in a very slow rate, we have to keep that particular, or we have
to maintain that particular environment sterile, for a prolonged time. So, maintenance of sterility
in that particular environment is a very difficult as far as the cell cultivation is concerned.
They are enclosed with a delicate plasma membrane, without a tough cell wall normally found in
microorganism and plant cells. As a result, they are very much fragile in nature. So,
I have told you that, animal cells do not have any cell wall. So, as it does not have
any cell wall, so, cell membrane is there; whereas, in microbial cell, we have learnt,
the cell wall, cell membrane; in case of a plant cells also, cell wall is there. So,
they are giving the extra protection and that protection is missing in case of animal cell;
obviously, the handling of animal cell is very tough, because, because of its fragile
nature; and that is the reason, why we are so much bothered about this animal cell cultivation
process. The nutritional requirements are not fully defined yet, requiring expensive
blood serum for the medium; because we are mimicking the body condition. And, that is
the reason why, this particular cell cultivation is so expensive. They are part of an organized
tissue, rather than an individual cellular organism; most of the animal cells only grow,
when attached to the surface.
So, these are all about this animal cell cultivation. So, when we have compared the animal cells
along with the plant and microbial cells, we have seen that, there is a significant
difference the microbial cell and animal cell, mammalian cell and so on. Where we are considering
the plant cell cultivation? Now, here, when we are talking about this plant cell, plant
cell has got cell wall, which has got the similarity with the microbial cell; microbial
cells also has got this, microbes, microbess has got cell wall. So, here, plant cells can
be cultivated where they are needed, regardless of the weather and the geographical condition.
The products, the product quality and yields, can also be well controlled by eliminating
the problems encountered in the processing of botanicals, such as the quality of the
raw material, uniformity within and among lots, and damage the shipment and storage.
Some metabolic, metabolic products can also be produced from the suspension culture in
higher quantities, than that is observed in the whole cell; and that is the reason, why
we are going for this plant cell cultivation.
Now, here also, this same problem; when we are comparing the growth rate of the plant
cell and any microbial cell, we generally find that, plant cells are growing in a much,
much slower rate and maintenance of sterility is a big problem as far as animal cells, as
well as plant cell cultivations are concerned. Now, if we see the different product which
has got commercial interest, we can find that, the metabolites which are produced by the
plant cells can be divided into two parts. One is called primary metabolites; another
is the secondary metabolites. When we are talking about the primary metabolites, the
production is of one type. When we are talking about the secondary metabolites, then only,
we are going for the different types of cell cultivation, molecular, biological approaches
and so on, or this macro propagation, and different techniques we are just talking about,
for plant cell cultivations too. Now, here, when we are talking about this
food products, it maybe colors, flavors, it can be oils, it can be any sweetener, it can
be any spices, that can be produced through plant cell cultivation. When we are talking
about the pharmaceuticals, we are talking about the alkaloids, we are talking about
steroids; we are, we are also talking about some foreign proteins and some other biochemicals,
which has got immense application as far as today’s world is concerned.
When we are talking about the agricultural sector, agro chemicals are playing a significant
role, which can also be produced through plant cell cultivation. And here, I have given you
some of the names, which are symbolic to this, plant tissue culture products. There are n
number of such products, which can be produced, which are being produced and isolated and
getting, and, and is applied, as far as today’s modern world is concerned.
Coming, to the microbial cell cultivation, now, why I am talking about all this cultivation,
this system, because, until and unless we know the plus point and the negative point
of each and every system, it will be very, very difficult for us to choose the actual
system for metabolite production; and until and unless we are selecting the system, we
cannot go for the large quantity production of the metabolite, which is of our own interest.
Now, when we are talking about this metabolic microorganisms as the means for cell cultivation,
then we can find that, microorganisms have been used by humans since prehistoric times
in the preparation of food, alcoholic beverages, milk product, textile and so on. Today the
use of microorganism is even more widespread than before. They are not are only used for
the traditional microbial processes, but also for new processes, such as production of pharmaceuticals,
industrial chemicals, enzymes, agricultural chemicals, waste water treatment, mineral
leaching, and recombinant DNA technology.
So, for any such, any products, which we have already learnt in today’s class, can be
possible through microbial intervention. And, that is the reason, why microbes or microbial
system is so popular. Now, if we see the advantages of this microbial cells over the plant cell
cultivation, then, we can find that, this plant cells are 10 to 100 times are larger,
than bacterial or any fungal cell; that means, obviously, size is more; it is eukaryotic;
bacterial or fungal system, it is mostly, this bacteria is prokaryotic in nature; and,
if we see the organizational development, though fungus is coming under eukaryotes,
but, their development is not that developed, compared to the plant cells.
Now, the metabolism of plant cells is slower than the microbial cells, as I have already
mentioned you earlier; in the order of magnitude which requires the maintenance of sterility
for a longer period of time, that I have already mentioned you. Cell culture tend to grow in
clumps, which cause sedimentation, poor mixing, plugging of inlet and outlet line, cell wall,
that wall growth and so on. So, it takes time; and maintenance of sterility is also very,
very important as far as this plant cells are concerned. And, there should not be any
microbial contamination, or any other contamination during this cell cultivation process. Plant
cells are more sensitive to shear than the microbial cell; those cell walls are there
in case of plants. Metabolic production in plant cells is subject to more complex regularity
mechanism than metabolic production of microbial cells. Plant cells are more genetically unstable
than the microbial cell, and that is the reason, why every time, the scientist, they are taking
the microbial cell as one of the means to express, either animal sources gene, or plant
resource, the gene from plant, plant resource and expression media which is selected, is
the microbial system.
Now, when we are going for the cultivation of this microbes, so, that is the reason,
the reason I have justified that, why microbes are generally considered for gene expression.
Now, cloning is successfully done, but expression is not there; that system cannot be considered
for further metabolite production. So, if we can successfully clone and express that
particular metabolite in the microbial system, then only, we can go for, we can consider,
that particular system for that metabolic production, or metabolite production. For
this, if we are selecting any microbes, then, we are generally going for the fermentation
system.
Now, in this fermentation system, we are, if we see, the entire fermentation system,
then we can divide the fermentation process into two major categories. One is the submerge
fermentation; another is the solid state fermentation. Nowadays, different types of fermentations
are coming to picture. Some of these fermentations are called modified solid state fermentation;
that means, whatever is this type of fermentation, some modification has been done and it is
coming under this modified solid state fermentation. Now, what is submerge fermentation and what
is solid state fermentation?
Now, suppose, we have taken a particular gene from a mammal, and from the, from that gene,
or any plant, whatever maybe the sources, and we have taken that gene, and we have cloned
it in a bacterial, in a plasmid DNA; and we express that thing in any bacterial system,
say for example, E coli, is one of the example. So, suppose, we had taken that particular
gene and we had expressed it for any metabolite production. Now, suppose, if it is from the
animal origin, so, suppose bfgf, that basic fibroblast growth factor; so, suppose we,
and this is the mammalian, that animal, this cell cultivation and it is a growth factor,
and we can, we have taken this gene from the parent tissue, and we have expressed that
thing in E coli; and we have seen that, this particular product is successfully getting
expressed in the bacterial system. Now, when we are going for the large scale production
of this particular metabolite, we are selecting the fermentation system.
Now, when we are going for this fermentation system, we are just taking this particular,
we know that, these are the different types of fermentation; one is the submerge; another
is the solid state fermentation. So, this e coli can be grown in different system. What
is submerge and what is solid state fermentation? Now, we have to have some idea about this,
what is submerge fermentation and what is solid state fermentation; then only, we can
go for any modification, that is modified solid state and so on. Now, what is solid
state and submerge fermentation? In submerge fermentation, the substrate is solubilized,
or suspended as fine particles in the large volume of liquid; that means, if we are considering
that conical flask as one of the media, and here, if we are taking some of this media,
liquid component of the media, and if we are just inoculating our, this E coli to grow
in this, then, we are just calling it, when excess liquid is there; the media is liquid,
that is called submerge fermentation; that means, everything is inside the surrounding
liquid. When there is no free flow liquid within the system, fermentation area, medium,
that, then we are calling it as solid state fermentation. In solid state fermentation,
the major difference is that, here, the media component, or the constituents which are there,
is in the soluble form. Here, we are taking insoluble biomasses, which are considered
to be the, the, the substrate for the growth of the organism, and there is no free flow
liquids are there. So, if we are considering the tray as the
bioreactor, then here, we are compiling the insoluble substrate and then, we are inoculating
the microorganism to this, and then, we are just growing the microorganism and there is
no free flow liquid. So, obviously, the aeration and whatever is there, through the surface
diffusion; and here, as this is the liquid medium, we can take any type of vessel, any
type of agitator, or any type of oxygen system, and with every control, we can go for the
production of our metabolite through the submerge fermentation. So, here, we had the different
types of different control system, and here, the oxygen transfer is mainly taking place
through the diffusion process. Now, here, some other problems which are associated
with the solid state fermentation is that, when we are inoculating the microorganism
to this insoluble substrate, the most of the reactions are exothermic in nature. Now, when
this exothermic reactions are going on within the system, then, what we are find that, lot
of heat is generated within this system; when heat is generated, then, temperature rise
within the bed is taking place. Sometimes, it has been seen that, from the top layer
to the bottom layer, a gradient of temperature which may exceed to 20 degree. Now, here,
when such rise of temperature is there, the biochemicals which are being secreted, which
are being produced by these living cells, microorganism, are getting denatured; because,
it has been seen that, most of the biochemicals are heat sensitive. And, that is the reason,
sometimes we have to have some water circulation, or some forced aeration, to move, remove the
heat which is being generated within this particular system. Now, these are some of
the advantages and disadvantages of this submerge fermentation and solid state fermentation.
Now, here, if we see the advantages of solid state fermentation over submerge fermentation,
then, we can find that, there are huge advantages of solid state fermentation, though it is
suffering from some problems; but, if we compare the solid state fermentation and the submerge
fermentation, then, we can see that, it is the low water demand, because no excess free
flow liquid is there in this particular fermentation system, and obviously, less water, waste water
is produced; high concentration of the end products are there, because here, whenever
the metabolites, they are secreting the products in this particular media, it is remaining
along with this insolubles; but here, as this is the liquid, this liquid, this, whatever
is the metabolites, this metabolites are getting diluted, and diluted within the entire volume
of this liquid; and that is the reason, why we have this dilution problem is so high,
in case of the submerge fermentation system. Now, here, if we see that, catabolite regressions
significantly lower, or almost missing, in case of this solid state fermentation. Utilization
of solid substrate is also there. We can use biomass as one of the raw material for any
metabolite production; that means, this metabolite production can be the sources, is of cheaper,
lower sterility demand, solid supports for the microorganisms are there; simulation of
the natural environment is also there; fermentation of water insoluble solid substrates are generally
taken as the raw material; mixed culture of microorganisms can also be attempted for better
productivity of the product. That processing advantages if we see, then, we can find that,
high volume productivity; that means, smaller fermented volume is giving the high productivity.
Low energy demand for heating, easy aeration, utilization of otherwise unstable carbon sources
are also there, which are cheap and abundant carbon sources are being utilized in this
process. No antifoam chemicals are to be added, because, no liquid is there; foaming problem
is not there, which is very, very means, probable problem in case of the submerge fermentation.
If we see the characteristics of solid state fermentation and submerge fermentation, then,
further, we can divide the two processes like this. It is a static process, this one is
the static process; we can go for agitation through, if we find that, the system is aerobic
in nature. Water uses in this particular solid state fermentation is limited, and in case
of submerge fermentation, the water use is unlimited. If we see the volume of fermentation
mass, this, it is, in case of solid state fermentation, it is smaller; in case of submerge
fermentation, a huge quantity of liquid handling is there. Oxygen supply, I have already told
you that, through diffusion, and here, in case of submerge fermentation, it is through
aeration. Liquid waste production is almost negligible in case of solid state fermentation,
and in case of submerge fermentation, it is significant. Physical energy requirement is
low in case of solid state fermentation, and in case of submerge fermentation, it is very
high. Human energy requirement is, in case of solid state fermentation, is high, whereas,
in case of submerge fermentation, it is low. Capital investment is low in case of solid
state fermentation, whereas, submerge fermentation, it is high.
Now, if we see, here, as this media is liquid, we can easily go for automation and with all
mechanical means, we can use with the machines; but, here, as I have told you that, this process
is being carried out through this solid state fermentation and here, the tray type of fermented
and this here, this system mechanic, the mechanization of this particular system, is very, very difficult,
and that is the reason, here, human intervention is very very needed; that is the reason, why
manpower requirement, in case of solid state fermentation is so high, compared to the submerge
fermentation. This is one of the disadvantage, disadvantages, what I have till now discussed.
But, lot of advantages are there, on this solid state fermentation over the submerge
fermentation.
Now, if we see the fermentation, overall fermentation system, irrespective of solid state or submerge,
we can find that, there are very many factors, which are playing a significant role, as far
as this particular fermentation is concerned. Now, selection of suitable substrate, selection
of efficient microorganism, that means, selection of microorganism, relative humidity of the
fermentation system, moisture content, amount and type of inoculums which are used for this
particular system, temperature of the system, production, that period of production, or
the incubation time for the products synthesis, these are some of the very, very important
parameters, which are playing a significant role, as far as the fermentation is concerned.
Now, if we see the suitable microorganism for a solid state fermentation, then, we can
find that, in most of the cases, if we see the architecture of the bacterial cell, these
are unicellular in nature; but, if we see the fungal cell, they are thread like hyaline
structure; and this hair like structure, they are getting cracked, or it forms a lump when
it is coming in contact with this liquid media. Sometimes, when, and this, this, this hair
like structure of this fungus are so delicate, once, with very minute handling problem, there
there that thread or the hifi may get cracked; once this hifi is getting cracked, all the
intracellular materials are coming out of this cell and as we have already discussed,
that lysozyme is there within the cell, and when lysozyme is there, lysozyme is one of
the product which is coming out of the cell to this surrounding medium; and when this
surrounding medium, this lysozyme is coming, it start damaging the intact cell; because
that is the suicidal enzyme, and it damage the total cell. And, that is the reason why,
while culturing the filamentous fungus, generally solid state fermentation is mostly preferred.
Now, here, this, this fungi, they serve a suitable microorganism for solid state fermentation,
because of the following reason. Fungi grow well in solid state fermentation by producing
hydrolytic enzyme and breaking their own organic material into inorganic minerals, mineral
compounds for the survival in nature. Fungi are able to withstand the limited water availability
in the solid substrate, and, and the conditions of solid state fermentation remains similar
to those of the natural habitat. Fungal spore can easily develop and proliferate on the
surface of the solid matrix, in solid state fermentation.
Now, these are some of these, this advantages, or the, the, the characteristics of some of
these microorganisms, which are forcing us to select such type of fermentation system.
And, when we are handling the filamentous fungi, mostly solid state fermentation system
is selected. Now, this particular, this, this particular solid state fermentation is otherwise
called as Koji fermentation.
Now, when we are talking about the solid state bioreactor, now, here, for large scale production
of such type of things, in the small tray, we can start, in small beakers or the Petri
plate also, we can consider those things as the reactor, that tray type of reactor and
we can start our work; and, when we are going for the large quantity, then, we are going
for the tray type of reactor. Now, in the laboratory, we are just starting it in a laboratory
scale, with the small tray, and when we are going for the pilot and the industrial scale,
then, I told you that, number of trays are getting increased, for the increased amount,
bulk production of the metabolites.
Now, when, in case of solid state fermentation, we are considering, it is without forced aeration
is there. It corresponds to the tray fermented as typified by the famous Koji processes.
A tray bioreactor consist of a chamber, in which the air is there with controlled temperature,
and relative humidity is circulated around the number of trays made up of wood, metal or
plastic. So, as I have told you that, as the metabolite, during metabolite production,
lot of heats are, heat is being generated; to reduce the temperature, that water circulation
is preferred. Each tray contain a thin layer of substrate, typically between 5 to 15 centimeter
deep, and usually has an open top and perforated bottom. The main disadvantages of this configuration
is that, this technology requires the numerous trays, large area, and it is labour-intensive;
and that room which is there, that, in that particular room, the controlled temperature
and humidity, both has to be maintained.
Now, when we are talking about the packed-bed unmixed solid state fermentations bioreactor,
it involves the static bed on top of the perforated plate, through which the conditions air is
blown. The main drawback of this configuration is that, it is difficult in obtaining the
product; that means, leaching out the product is difficult; non-uniform growth of the microorganism
is also there; poor heat removal and scaling up problem are associated with this.
Now, when we are going for the continuously rotating drum and intermittent mixing bed
bioreactor with forced aerations, we can overcome some of the problems associated with this
type of static process. Now, in this rotating drum, drum is getting rotated in a very slow
speed, and fermentation within that insoluble matrix are going on, and it is getting that
rotation, and it is getting the aeration, and surface area also, it is getting throughout
the drum, and that with a very low speed, the substrates are moving, and this, your,
in a, in a horizontal drum, where, which may not have baffle, and which is rotated continuously,
for such type of product formation. For a discontinuously rotating drum, the design
is identical to that of a continuously rotating drum. Now, here, when we are going for the
mixed bed bioreactor with forced aeration, now, here, we are just giving the aeration,
forced aeration to drag the heat out of this particular bed.
And, when we are going for this classification of this process, we can go for the batch process,
continuous process, fed-batch process and so on. Now, in case of this solid state fermentation,
fed-batch process, continuous process, is very, very difficult to maintain, for which,
we can switch over to the submerge fermentation. Now, when we are going for this submerge fermentation,
this submerge fermentation is totally different from that of the solid state fermentation.
Now, here, in case of continuous fermentation, one group of tray is entering, and one group
of tray is going out; continuously there is a flow, and with a certain incubation time,
that trays are going out continuously, and that is the continuous fermentation process.
But, independent trays are being handled, if irrespective of whether, it is a continuous,
or it is a batch process. In case of submerge fermentation, here, the control system is
totally different from that of this solid state fermentation. So, in our next class,
we will be discussing on the solid state, that is, a submerge fermentation and how this
submerge fermentation is being taken care of by different types of reactor, for the
production of different biochemicals of our own interest; we will learn that. Thank you
very much.