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Microbial Growth Kinetics Lecture 2. Fermentation Process.

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Presentation on theme: "Microbial Growth Kinetics Lecture 2. Fermentation Process."— Presentation transcript:

1 Microbial Growth Kinetics Lecture 2

2 Fermentation Process

3 Types of Culture Fermentation - carried out as batch, continuous and fed-batch Dictated largely by type of product being produced

4 Batch Culture Closed culture system – initially contains limited amount of nutrient No growth – lag phase – time of adaptation Growth rate increases – grow constantly at maximum rate – Log or exponential phase

5 Batch Culture- Exponential phase/Trophophase Exponential phase equation: dx/dt = µx where x is the concentration of microbial biomass, t is time in hours and µ is the specific growth rate in hours Nutrients are in excess and organism is growing at its maximum specific growth rate = µmax

6 Batch Culture – Deceleration phase Cessation of growth – due to depletion of some essential nutrient in medium (substrate limitation) Accumulation of some autotoxic product of organism in medium (toxin limitation) Or combination of both

7 Batch Culture – Stationary phase/Idiophase Point where growth rate has declined to zero. Population is metabolically active – producing secondary metabolites Maximum population phase

8 What is Yield Factor (Y)? It is a measure of efficiency of conversion of any one substrate into biomass. It is not constant – varies according to growth rate, pH, temperature, the limiting substrate and concentration of substrates in excess.

9 How can deceleration phase be tested? Zone A to B – increase in initial substrate concentration – proportionally increases biomass produced at stationary phase x=Y(Sr-s) where x is concentration of biomass produced Y is yield factor, Sr is initial substrate con. and s is residual conc.

10 Growth kinetics of Metabolites Growth-linked products/Primary metabolites Formation of growth linked product is described by equation -dp/dt = qpx where p is the concentration of the product -qp is specific rate of product formation (mg product/g biomass/h) -Product formation is related to biomass production by equation dp/dx = Yp/x -Where Yp/x is the yield of product in terms of biomass (g product/g biomass)

11 Batch fermentation – used for? Producing biomass – fastest growth rate and maximum cell population Primary metabolites – extend exponential phase Secondary metabolites – decreased growth in log phase

12 Continuous Culture (Chemostat) Addition of fresh medium to the vessel – exponential growth Medium is substrate limited Overflow device – added medium displaces equal volume of culture – continuous production of cells - Formation of new biomass balanced by loss of cells from vessel

13 Chemostat culture Chemostat culture – Cells and spent medium are continuously removed - State of culture is dependent upon flow rate of fresh medium

14 Continuous Culture (Chemostat) Dilution rate - The flow of medium into the vessel is related to volume of the vessel D = F/V - F is flow rate (dm3/h) - V is volume (dm3) -D is dilution rate in per hour -Net change in cell concentration over a time period = dx/dt = growth (µx) – output (Dx)

15 Problems - Chemostat Problems – Imperfect mixing and wall growth -Imperfect mixing – increase in degree of heterogeneity in fermenter -Wall growth – Organism adheres to inner surfaces of reactor – increases heterogeneity -Limited by coating inner surfaces of vessel with Teflon

16 Feedback systems - Chemostat Internal feedback – Limiting exit of biomass External feedback – Subjecting effluent stream to biomass separation

17 Perfusion/Turbidostat Perfusion culture - Medium is pumped continuously -Cells are retained -Becoming popular for large-scale production -Attains high cell density -Cell separator

18 Continuous culture Biomass production Microbial biomass produced for human or animal consumption – Single Cell Protein (SCP) Practice 1960s

19 What is Fed-batch culture? In open system/Fed-batch culture – involves controlled nutrient feeding Partial media changes at regular intervals

20 Fed-batch culture Initial batch cultures – fed continuously or sequentially with medium No removal of culture fluid Three types – Variable volume, Fixed volume and Cyclic fed-batch

21 Fed-batch culture Batch culture is fed in following ways -Same medium + conc. used to establish batch culture is added –Variable volume - Conc. solution of limiting substrate is added at a rate less than initial -Very conc. Solution of limiting substrate at lesser rate than initial – Fixed volume

22 Cyclic fed-batch culture Life of variable fed-batch fermentation may be extended -Withdrawing a portion of culture/residual culture -Increase in dilution rate and specific growth rate

23 Fed-batch culture Used for biomass Primary metabolite Secondary metabolite

24 This project is funded by a grant awarded under the President’s Community Based Job Training Grant as implemented by the U.S. Department of Labor’s Employment and Training Administration (CB ). NCC is an equal opportunity employer and does not discriminate on the following basis: against any individual in the United States, on the basis of race, color, religion, sex, national origin, age disability, political affiliation or belief; and against any beneficiary of programs financially assisted under Title I of the Workforce Investment Act of 1998 (WIA), on the basis of the beneficiary’s citizenship/status as a lawfully admitted immigrant authorized to work in the United States, or his or her participation in any WIA Title I-financially assisted program or activity.

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