bio proses untjk mahaisawa teknik kimia dan untuk mahasiwa biologi

7/27/2019 bio proses untjk mahaisawa teknik kimia dan untuk mahasiwa biologi

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MICROBIAL GROWTH

KINETICS-In Batch System-


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deals with the rate of cell growth important for the design and operation of

fermentation systems employing them

An ideal culture for fermentation should (be):1. pure.2. grow and reproduce quickly.3. genetically stable yet easy to manipulation for

better performance.

4. produce uniform product in a short time.5. not produce undesirable by-products.6. have a protective mechanism against other

undesirable contaminants.


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BATCH SYSTEM

close system, without any inlet or outletstreams

nutrients are fixed amount limited

The inocula are transferred, thengradually grow and replicate

As the cell propagates, the nutrients are

depleted and end products are formed Main stages of a growth curve: lag,

exponential, stationary & death phases


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Lag phase

the cell number does notincrease

the cells may grow in size

duration of time foradaptation ofmicroorganisms to thenew environment,without much cellreplication and with no

sign of growth. shock to the environment

when there is noacclimation period


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Length of lag phase inoculum (concentration, type,age), medium composition, fermentation conditions

i) Medium Transfer microorganisms from a low nutrient to high

concentration long lag period, because the cellsmust produce the enzymes necessary forthemetabolization of the available nutrients.

If they are moved from ahigh to a low nutrientconcentration short lag phase

ii) size of the inoculumIf a small amount of cells are inoculated into a largevolume a long lag phase.


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Short lag phase

Excessive lag phase unproductive

Minimize lag phase period:

1. the composition of the medium and theenvironmental conditions in the seed culture and

the production vessel are identical2. the dilution shock is small (i.e. a large amount of

inoculum is used)

3. the cells in the inoculum are in the late

exponential phase of growth.


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Exponential phase

The stages:

i) Accelerated growth phase: The cell number starts toincrease and the division rate increases to reach amaximum sometimes included as part of lag phase

ii) Exponential growth phase: The cell number increasesexponentially as the cells start to divide

Plotting the linear increase growth in semi-log graphshown a constant slope

Slope representing a constant rate of cell population

ii) Decelerated growth phase: After the growth ratereaches a maximum, it is followed by the decelerationof both growth rate and the division rate

Primary metabolism products in tropophase periode


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Stationary phase

The cell population will reach a maximum value will not increase any further growth rate zero

cell density remains constant The growth of microbial populations is normally

limited either by the exhaustion of available nutrientsor by the accumulation of toxic products ofmetabolism the rate of growth declines and growtheventually stops

The transition between the exponential phase and thestationary phase involves a period of unbalanced

growth during which the various cellular componentsare synthesized at unequal rates. Consequently, cells in the stationary phase have a

chemical composition different from that of cells in theexponential phase


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However, in this phase metabolisms arestill active

Produce compounds are not synthesized

during tropophase (exp. Phase)secondary metabolism, no obviousfunction in cell metabolism

idiophase

employ primary products as raw material very few microorganism species; not all


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Death phase

activities of the cell gradually decrease as they age In the end of stationary phase cell may start to die

Death occurs either because of the depletion of thecellular reserves of energy, or the accumulation oftoxic products deactivating remaining cells

the cell growth rate balances the death rate. In some cases, the organisms not only die but also

disintegrate, a process called lysis. a death phase develops while the cell density

drastically drops if the toxic secondary metabolites

are present exponential decrease in the number of living cells in

the media while nutrients are depleted.


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KINETICS OF BATCH SYSTEM

The objective of design is to minimise the lag phaseperiod and maximise the length of exponential growthphase

cell kinetics is the result of numerous complicatednetworks of biochemical and chemical reactions and

transport phenomena, which involves multiple phasesand multicomponent systems the concentration of nutrients, cells (old & new) and

products vary with time as the growth proceeds. living cells propagate and many parameters of the

media go through sequential changes with time as thecells grow

As a result, accurate mathematical modeling ofgrowth kinetics is impossible to achieve

The simplest model unstructured, distributed rnodel


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..assumptions of the model..1. Cells can be represented by a single component (e.g cell

mass, cell number, the concentration of protein, DNA, orRNA.This is true for balanced growth, since a doubling of cellmass for balanced growth is accompanied by a doubling of allother measurable properties of the cell population.

2. The population of cellular mass is distributed uniformly

throughout the culture.The cell suspension can be regarded as a homogeneoussolution. The heterogeneous nature of cells can be ignored The cell concentration can be expressed as dry weight perunit volume(g/l) or cell optical density (absorbance at adefine wavelength).

3. the medium is formulated so that only one component maybe limiting the reaction rate. All other components are present at sufficiently highconcentrations, so that minor changes do not significantlyaffect the reaction rate.

4. Fermenter are also controlled so that environmental

parameters such as pH, temperature, and dissolved oxygenconcentration are maintained at a constant level


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On exponential growth phase

In unicellular organisms, the progressive doublingof cell number results in a continually increasingrate of growth in the population

Assumption: the growth rate based on the cell

number proportional to that based on cell weight A bacterial culture undergoing balanced growth

mimics a first-order autocatalytic chemical reaction

Therefore, the rate of the cell population increase

at any particular time is proportional to the numberdensity (CN) of bacteria present at that time:


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(specific growth rate, t-1)

The growth rate is the change of the cell numberdensity with time

the specific growth rate is the change of thenatural log of the cell number density with time.

CN is the cell number concentration at t0 when theexponential growth starts


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when is constant with time during theexponential growth period, then

Taking natural log. when t0=0, becomes:Ln CN=ln CN0+ t

The time required to double the population(CN=2CN0), called the doubling time (td),

The doubling time is inversely proportional to thespecific growth rate


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During exponential phase, nutrients are in excess& organism grows at its max specific growth rate(max)

Growth results in consumption of nutrients &

excretion of microbial products After certain time the growth rate decrease until

growth ceases

The ceases may be due to depletion of nutrients(substrate limitation), accumulation of autotoxic,or combination of the two


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Factors Affecting

1) Substrateconcentration

Cs = concentration ofthe limiting substrate.

Ks is equal to theconcentration of

nutrient when thespecific growth rate ishalf of its max value(max)


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According to the Monod equation, furtherincrease in the nutrient concentration afterreaches maxdoes not affect the specific growthrate,

specific growth rate decreases as the substrateconcentration is increased beyond a certain level.


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2) 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 tothe Monod equation as follows:

3) Other Conditions

medium pH, temperature, and oxygen supply The optimum pH and temperature differ from one

microorganism to another.


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Paper assignment

TOPICS

Baker yeast

Single cell protein

Pectinase protease

Glutamic acid

dextran

Insuline

penicilline

THE POINTS

Medium

Microorganism

Medium state Reaction conditions

The use

etc

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