BATCH AND CONTINUOUS FERMENTATION
SOLID STATE FERMENTATION
Fermentation is the oldest form of biotechnology, essentially consisting of transformation of the simple raw materials into value added amazing range of products by utilizing the growth of microorganism.
The basic purpose of micro organisms to break down the organic compounds is to get energy for their metabolic process.
Some fermented products
A batch fermentation is regarded as a closed system.
The sterile nutrient culture medium in the bioreactor is inoculated with micro organisms.
The incubation is carried out under optimal physiological conditions.
It may be necessary to add acid or alkali to maintain pH and antifoam agents to minimize foam under optimal conditions for growth.
Under optimal conditions for growth the following typical phases of growth, are observed in batch fermentation.
Logarithmic (log) phase (exponential phase)
Initial period of culturing after inoculation is referred to as lag phase.
During the lag phase, the micro organisms adopt to the new environment avaliable nutrients, pH etc.,
There is no increase in the cell number, although the cellular weight may slightly increase.
It is a brief transient period during which cells start growing slowly.
This phase connects the lag phase and log phase.
The most active growth of micro organisms and multiplication occur during log phase.
The cells undergo several doublings and the cell mass increase when the number of cell or biomass is plotted against time on a semi logarithmic graph, a straight line is obtained.
Growth rate of microbes in log phase is dependent on substrate (nutrient supply)
The substrate in the growth medium gets depleted and the metabolic and products that are formed inhibit the growth, the cells enter the stationary phase.
The microbial growth may either slow down or completely stop.
The biomass may remain almost constant during this phase
The cells die at an exponential rate.
In the commerical and industrial fermentation, the growth of the microbes is the end of the log phase or just before the death phase begins and the cells harvested.
It is an open system.
It involves the removal of culture medium continuously and replacement of this with a fresh sterile medium in a bioreactor.
Both addition and removal are done at the same rate so that the working volume remains constant.
Homogenously mixed Bioreactors
In this type, the culture solution is homogenously mixed
The bioreactors are of two types
The concentration of any one of the substrate is adjusted to control the cell growth and maintain a steady state.
In this case, turbidity measurement is used to monitor the biomass concentration.
The rate of addition of nutrient solution can be appropriately adjusted to maintain a constant cell growth.
SOLID STATE FERMENTATION
Most fermentation technologies using microbes employ a fairly dilute medium where the substrate to be fermented is diluted in water and then inoculated with desired microbes.
Some fungai can grow in conditions without free water.
In this case the moisture required by the fungus exists than absorbed or complex form in the solid matrix , often ranging between 10% and 80% processes which exploit the growth of fungai in this type of system are designated solid state fermentation.
EXAMPLES FOR SOLID SUBSTRATE FERMENTATION
WINE MAKING FERMENTOR
A fermentor is a device in which the organisms are cultivated and motivated to form a desired product
Closed vessel or containment designed to give a right environment for optimal growth and metabolic activity of the organism
Fermenter: for microbes/ Bioreactor : for eukaryotic cells
Size variable ranging from 20-250 million litres or more.
Large scale production (10-100L to1000-million L capacity)
Regular monitoring for physical, chemical biological parameters is done through controlled systems of the fermentor, because these parameters influnces the growth of the microbes.
As per requirements and use of types of microorganisms there are different types of fermentors available.
The most common among these is stirred tank fermentor where impellers used to stirr the medium.
Helps to meet requirements of:
drain or overflow
cooling to achieve maximum microbial yield
The increasing concentration of microbial cells will deplete the dissolved O2 concentration resulting in creation of anaerobic conditions.
The microbial growth will simultaneous decline in product production.
The forced aeration favours rapid growth of micro organisms.
A pH fitted with fermentor regularly monitors the pH and maintains at optimum by adding acid or alkali.