Transcript Continuous & Batch Fermentation

Continuous & Batch
Fermentation
Making Useful Products From
Micro-organisms
Fermentation is a process which takes place when micro organisms
grow and multiply e.g. in beer, wine, yoghurt and myco-protein
production. Fermentation takes place in a container called a
'fermenter'
The fermenter is a vessel which is sterilised to provide a 'clean
environment' ensuring that only the desired organism grows.
The vessel is set up to provide the best growth conditions for
each culture of micro organisms according to its needs, whether
it be the manufacture of alcohol as in beer, or simply the growth
of myco-protein
Fermenter
Whether producing beer, wine, yoghurt or myco-protein
certain conditions are needed.
These include:
•sufficient nutrients
•enough air, and
•constant temperature
To ensure the culture has sufficient food and oxygen the
contents of the fermenter must be constantly mixed. These
conditions are provided by two different types of
fermenter.
Mechanical stirring using a paddle or magnetic stirrer in
the fermenter vessel.This method is often used in small
fermenters.
A pressure cycle fermenter uses the movement of air
within the fermenter to effect mixing.
Fermentation either takes place as a 'batch' process where
each filling of the fermenter gives a batch of finished
product, or a 'continuous' process where nutrients are added
and product removed continuously over the period of an
extended run.
In myco-protein production the removal of product from the
fermenter (called harvesting) only begins when the rate of
multiplication matches the rate of harvesting.
Growing Myco-Protein
Growing Conditions
As with any controlled growing procedure, the
conditions for this fermentation must be carefully
monitored. Therefore the fermenter is designed to allow
temperature, pH, nutrient, and oxygen levels to be
maintained at the levels required for optimum growth.
All the nutrients used in the process are of food grade
quality or higher, and the water is specially purified
before being added to the fermenter.
The Process
The fermenter is filled with water and the relevant
nutrients added at the exact concentrations. A starter
culture of the organism is added and the fermentation
process begins (i.e. the cells begin to multiply). This
multiplication is allowed to continue until the number of
cells in the fermenter (the cell density) is such that some
of the contents of the fermenter can be removed without
altering the number of cells in the fermenter. This is
possible because the cells are multiplying at the same
rate as they are being removed. Removal of some of the
contents from the fermenter is called the harvesting
process.
Harvesting
Harvesting takes place by pumping the suspension of cells
and liquid removed from the fermenter through a heated
vessel which stops growth and renders the cells non-viable.
The suspension is then passed to a series of centrifuges
where the cells are separated from the liquid residue, and
these centrifuged cells are collectively known as mycoprotein. The myco-protein is placed in containers and
refrigerated ready to be used as the major ingredient in the
manufacture of the Quorn™ ™ product range.
Process of Mycoprotein
Production
Myco-protein has a high nutritional value, which makes it
an ideal food ingredient.
The sole current use for myco-protein is as the major
ingredient in the manufacture of the Quorn™ range of
meat alternative products. The process involved in their
manufacture includes simulating meat product structures
by binding the myco-protein cells together with the other
ingredients in the recipe. This mimics the muscle fibre /
connective tissue interaction in muscle tissue.
This is achieved by mixing the myco-protein with a
binder (and all the other ingredients in the product
recipe) forming the required shape of the product, and
then steaming the shaped material to heat-set the binder.
After heating, the products are chilled, packed and
distributed for retail sale.
Final Processing
Ethanol Fermenter
Continuous Fermentation of Ethanol
The traditional processes for making alcoholic
beverages are batch operations that take days or weeks.
Industrial ethanol for solvents and other uses was made
from petroleum for several decades because cost was
less than for fermentation. When the price of petroleum
rose sharply in the 1970's, the economics were better for
fermentation ethanol but not for the slow processes.
Various improvements such as more energy efficient
distillation or drying, recycle of medium that still had
valuable nutrients, and better process control apply to
either batch or continuous processing. The two types of
continuous processing employ some means of retaining
yeast cells in the bioreactor. The tower fermentor uses a
strain of yeast that flocculates to particles that fall back
as the fluid rises to an expanding conical section above
the main region for bioreaction..
Fed batch Reactors
Comparison of fed-batch and continuous
bioreactors.
With both fed-batch and continuous fermenters
it is possible to set and maintain the specific
growth rate and substrate concentration at
optimal levels.
The major physical difference between a fedbatch and continuous fermenter is that the
effluent is not continuously removed and thus
washout does not occur.
This provides a fed-batch reactor a number of
advantages over continuous reactors:
•A fed batch reactor can be
operated in a variety of ways. For
example, the reactor can and often
must be operated in the following
sequence:
•Batch => Fed-batch => Batch
The feed can also be manipulated
to maximize product formation.
For example, during a
fermentation, the feed composition
and feed flow rate can adjusted to
match the physiological state of the
cells.
Because cells are not removed during the fermentation, fedbatch fermenters are well suited for the production of
compounds produced during very slow or zero growth.
•Unlike a continuous fermenter, the feed does not need
to contain all the nutrients needed to sustain growth. The
feed may contain only a nitrogen source or a metabolic
precursor.
•Contamination will also not have the same
dramatic effect on a fed-batch fermenter as a
contaminant will not be able to completely take
over the fermenter (unless the contamination
occurred during the early stages of the
fermentation).