Etiket Arşivleri: Lag phase

Food Biotechnology ( N.INDRA )







  • N.INDRA .


  • 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.


  • Lag phase

  • Acceleration phase

  • Logarithmic (log) phase (exponential phase)

  • Deceleration phase

  • Stationary phase

  • Death 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.


  • Acceleration phase

  • It is a brief transient period during which cells start growing slowly.

  • This phase connects the lag phase and log phase.

  • 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

  • Death 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

  • Chemostat bioreactors

The concentration of any one of the substrate is adjusted to control the cell growth and maintain a steady state.

  • Turbidostat bioreactors

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.


  • 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.





  • 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

control systems


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.

Chapter 5 ( Dr. Ali Coşkun DALGIÇ )


Cell Kinetics and Fermenter Design
§Understanding the growth kinetics of microbial, animal, or plant cells is important for the design and operation of fermentation systems employing them. Cell kinetics deals with the rate of cell growth and how it is affected by various chemical and physical conditions.
Unlike enzyme kinetics, cell kinetics is the result of numerous complicated networks of biochemical and chemical reactions and transport phenomena, which involves multiple phases and multicomponent systems.
The heterogeneous mixture of young and old cells is continuously changing and adapting itself in the media environment which is also continuously changing in physical and chemical conditions. As a result, accurate mathematical modeling of growth kinetics is impossible to achieve. Even with such a realistic model, this approach is usually useless because the model may contain many parameters which are impossible to determine

1. Lag phase: The lag phase (or initial stationary, or latent) is an initial period of cultivation during which the change of cell number is zero or negligible. Even though the cell number does not increase, the cells may grow in size during this period.

The length of this lag period depends on many factors such as the type and age of the microorganisms, the size of the inoculum, and culture conditions.

2. Exponential phase: In unicellular organisms, the progressive doubling of cell number results in a continually increasing rate of growth in the population. A bacterial culture undergoing balanced growth mimics a first-order autocatalytic chemical reaction.

The rate of the cell population increase at any particular time is proportional to the number density of bacteria present at that time:

Factors affecting the specific growth rate

Substrate Concentration: One of the most widely employed expressions for the effect of substrate concentration on μ is the Monod equation, which is an empirical expression based on the form of equation normally associated with enzyme kinetics :

The value of Ks is equal to the concentration of nutrient when the specific growth rate is half of its maximum value μmax. According to the Monod equation, further increase in the nutrient concentration after μ reaches μmax does not affect the specific growth rate.

Factors affecting the specific growth rate

Product Concentration: As cells grow they produce metabolic byproducts which can accumulate in the medium. The growth of microorganisms is usually inhibited by these products, whose effect can be added to the Monod equation as follows:

3. Stationary phase: The growth of microbial populations is normally limited either by the exhaustion of available nutrients or by the accumulation of toxic products of metabolism. As a consequence, the rate of growth declines and growth eventually stops. At this point a culture is said to be in the stationary phase.

4. Death phase: The stationary phase is usually followed by a death phase in which the organisms in the population die. Death occurs either because of the depletion of the cellular reserves of energy, or the accumulation of toxic products. Like growth, death is an exponential function. In some cases, the organisms not only die but also disintegrate, a process called lysis.

Modeling of the Bacterial Growth Curve




Stirred Tank Fermenters
A bioreactor is a device within which biochemical transformations are caused by the action of enzymes or living cells. The bioreactor is frequently called a fermenter whether the transformation is carried out by living cells or in vivo cellular components (enzymes).

For a large-scale operation the stirred-tank fermenter (STF) is the most widely used design in industrial fermentation. It can be employed for both aerobic or anaerobic fermentation of a wide range of cells including microbial, animal, and plant cells.

Stirred Tank
Kinetics of Substrate Utilization, Product Formation, and Biomass Production in Cell Cultures
It is difficult to obtain useful kinetic information on microbial populations from reactors that have spatially no uniform conditions. Hence it is desirable to study kinetics in reactors that are well mixed.

Ideal Batch Reactor

Many biochemical processes involve batch growth of cell populations. After seeding a liquid medium with an inoculum of living cells, nothing (except possibly some gas) is added to the culture or removed from it as growth proceeds. Typically in such reactor, the concentrations of nutrients cells, and products vary with time as growth proceeds.
A material balance on moles of component i;

The Ideal Continuous Flow Stirred Tank Reactor (CSTR)
The diagram of this process is shown in fig.2, which is a schematic diagram of completely mixed stirred tank reactor. Such configurations for cultivation of cells are frequently called chemostats.

The Ideal Continuous Flow Stirred Tank Reactor (CSTR)

Productivity of CSTF
A question arises frequently whether it may be more efficient to use multiple fermenters connected in series instead of one large fermenter. Choosing the optimum fermenter system for maximum productivity depends on the shape of the l/rx versus Cx curve and the process requirement, such as the final conversion.

Cell Recycling
For the continuous operation of a PFF or CSTF, cells are discharged with the outlet stream which limits the productivity of fermenters. The productivity can be improved by recycling the cells from the outlet stream to the fermenter.

Alternative Fermenters
Many alternative fermenters have been proposed and tested. These fermenters were designed to improve either the disadvantages of the stirred tank fermenter-high power consumption and shear damage, or to meet a specific requirement of a certain fermentation process, such as better aeration, effective heat removal, cell separation or retention, immobilization of cells, the reduction of equipment and operating costs for inexpensive bulk products, and unusually large designs.