effects of environmental conditions on growth kinetics
TRANSCRIPT
Effects of Environmental Conditions on
Growth Kinetics
Effects of Environmental Conditions on
Growth Kinetics
Effects of environmental conditions on growth kinetics
How environment conditions affect growth kinetics?
How environment conditions affect growth kinetics?
Environmental conditions: temperature, pH and dissolved-oxygen
concentration
Temperature affects the performance of cells. Organisms can be classified in 3 groups:1)Psychrophiles (Topt < 20°C)2)Mesophiles (Topt = 20 to 50 °C)3)Thermophiles (Topt > 50°C)As the temperature is increased toward optimal growth
temperature, the growth rate approximately doubles for every 10 °C increase in temperature.
As the temperature is increased toward optimal growth temperature, the growth rate approximately doubles for every 10 °C increase in temperature.
Above the optimal temperature range, the growth rate decreases and thermal death may occur. The net specific replication rate can be expressed by Eq. 9.19 (for temperature above optimal level):
At high temperatures, the thermal death rate exceeds the growth rate, which causes a net decreases of viable cells.
Both uR and kd vary with temperature according to the Arrhenius equation:
Where Ea and Ed are activation energies for growth and thermal death.
Ea (10-20 kcal/mol)Ed (60-80 kcal/mol)
Thermal death is more sensitive to temperature changes than the microbial growth.
Microbial growth
Product formation
Temperature also affects product formation.Temperature optimum for product formation and growth is different.The yield coefficient (Yx/s) is also affected by temperature. Example: a single-cell protein production. When temperature above the optimum temperature, the maintenance requirements of cells increase, resulting a decrease in the yield coefficient.
Temperature also affects product formation.Temperature optimum for product formation and growth is different.The yield coefficient (Yx/s) is also affected by temperature. Example: a single-cell protein production. When temperature above the optimum temperature, the maintenance requirements of cells increase, resulting a decrease in the yield coefficient.Rate-limiting step in
fermentationAt high temperatures, the rate of bioreaction might become higher than the diffusion rate, and the diffusion then would be the rate-limiting step.
Example:An immobilized cell system. The activation energy of molecular diffusion =6 kcal/mol. The activation energy of most bioreaction is 10 kcal/mol. So diffusion limitation must be carefully considered in high temperatures
At high temperatures, the rate of bioreaction might become higher than the diffusion rate, and the diffusion then would be the rate-limiting step.
Example:An immobilized cell system. The activation energy of molecular diffusion =6 kcal/mol. The activation energy of most bioreaction is 10 kcal/mol. So diffusion limitation must be carefully considered in high temperatures
Hydrogen-ion concentration (pH)
Affect the activity of enzymes and therefore the microbial growth rate.The optimal pH for growth may be different from that for product formation.
Different organisms have different pH optima:1.Bacteria (pH 3 to 8)2.Yeast (pH 3 to 6)3.Molds (pH 3 to 7)4.Plant cells (pH 5 to 6)5.Animal cells (pH 6.5 to 7.5)
Many organism have mechanism to maintain intracellular pH at relatively constant level in the presence of fluctuations in environmental pH
When pH differs from the optimal value, the maintenance-energy requirement increase
One consequence of different pH optima is that the pH of the medium can be used to select one organism over another.
Many organism have mechanism to maintain intracellular pH at relatively constant level in the presence of fluctuations in environmental pH
When pH differs from the optimal value, the maintenance-energy requirement increase
One consequence of different pH optima is that the pH of the medium can be used to select one organism over another.
AMMONIA (NH3)If ammonium is the sole nitrogen source, hidrogen ions are released into the medium as a result of the microbial utilization of ammoniaResulting in a decrease in pH
NITRATE If nitrate is the sole nitrogen source, hydrogen ions are removed from the medium to reduce nitrate to ammoniaResulting in an increase in pH
ORGANIC ACID PRODUCTION / BASES
pH can change because of organic acid or bases production
In most fermentation, pH can change or vary substantially by:
SUPPLY OF CO2
Seawater or animal cell
Variation of specific growth rate with pH is depicted by Figure 6.8
Dissolved OxygenDissolved Oxygen
Important substrate in aerobic fermentations and may be a limiting substrateAt high cell concentrations, the rate of oxygen consumption may exceed the rate of oxygen supply, leading to oxygen limitationWhen oxygen is the rate-limiting factor, specific growth rate varies with dissolved-oxygen concentration; below a critical concentration, growth or respiration approaches a first-order rate dependence on the dissolved-oxygen concentration.Above a critical oxygen concentration, the growth rate becomes independent of the dissolved-oxygen concentration.
Figure 6.9 depicts the variation of specific growth rate with dissolved oxygen concentration.
O2 is a growth-rate limiting factor when the DO level is below the critical DO concentration. In this case, another medium component (glucose, ammonium) becomes growth-extent limiting.
EXAMPLE: Azotobacter vinelandii at a DO = 0.05 mg/l, the growth rate is about 50% of maximum, even if a large amount of glucose is present.
However, the maximum amount of cells formed is not determined by the DO, as the O2 is continually resupplied. If glucose were totally consumed, growth would cease even if DO = 0.05mg/l.
Thus the extent of growth (mass of cells formed) would depend on glucose, while the growth rate for most of the culture period would depend on the value of DO.
O2 is a growth-rate limiting factor when the DO level is below the critical DO concentration. In this case, another medium component (glucose, ammonium) becomes growth-extent limiting.
EXAMPLE: Azotobacter vinelandii at a DO = 0.05 mg/l, the growth rate is about 50% of maximum, even if a large amount of glucose is present.
However, the maximum amount of cells formed is not determined by the DO, as the O2 is continually resupplied. If glucose were totally consumed, growth would cease even if DO = 0.05mg/l.
Thus the extent of growth (mass of cells formed) would depend on glucose, while the growth rate for most of the culture period would depend on the value of DO.
Ccrit = 5 to 10% of the saturated DO concentration (bacteria and yeast)
Ccrit = 10 to 50% of the saturated DO concentration (mold cultures)
Saturated DO concentration in water at 25°C and 1 atm pressure = 7ppm
Therefore the presence of dissolved salts and organics can alter the saturation value, while increasingly high temperatures decrease the saturation value
Saturated DO concentration in water at 25°C and 1 atm pressure = 7ppm
Therefore the presence of dissolved salts and organics can alter the saturation value, while increasingly high temperatures decrease the saturation value
O2 transfer from gas bubbles to cells is usually limited by oxygen transfer through the liquid film surrounding the gas bubbles.
The rate of oxygen transfer from the gas to liquid phase is given by:
kL = oxygen transfer coefficient (cm/h)a = the gas-liquid interfacial area (cm2/cm3)kLa = the volumetric oxygen transfer coefficient (h-1)C* = saturated DO concentration (mg/L)CL = the actual DO concentration in broth (mg/L)NO2 = rate of oxygen transfer (mg O2/l.h)OTR = Oxygen Transfer Rate
Oxygen Transfer Rate (OTR)Oxygen Transfer Rate (OTR)
Oxygen Uptake Rate (OUR)
qO2 = specific rate of oxygen consumption (mg O2/g dw cells-h)Yx/o = yield coefficient on oxygen (g dw cells / g O2)X = cell concentration (g dw cells / l)
qO2 = specific rate of oxygen consumption (mg O2/g dw cells-h)Yx/o = yield coefficient on oxygen (g dw cells / g O2)X = cell concentration (g dw cells / l)
When oxygen is the rate –limiting step, the rate of O2 consumption is equal to the rate of oxygen transfer.
or
Redox potentialRedox potential
Parameter that affects the rate and extent of many oxidative-reductive reactions
In a fermentation medium, the redox potential is a complex function of DO, pH, and other ion concentrations (reducing and oxidizing agents).
The electrochemical potential of fermentation medium can be express by the following equation:
To reduce the redox potential of a fermentation media – (N2, cystein HCL, Na2STo increase the redox potential – O2, oxidizing agents
Dissolved Carbon Dioxide (DCO2)Dissolved Carbon Dioxide (DCO2)
DCO2 concentration in medium fermentation may have effect on performance of organism.
Very high DCO2 concentration may be toxic to some cells
Cells require a certain DCO2 level for proper metabolic functions.
DCO2 in medium can be controlled by:1.Changing the DCO2 content of the air supply2.Agitation speed
DCO2 concentration in medium fermentation may have effect on performance of organism.
Very high DCO2 concentration may be toxic to some cells
Cells require a certain DCO2 level for proper metabolic functions.
DCO2 in medium can be controlled by:1.Changing the DCO2 content of the air supply2.Agitation speed
Ionic Strength of Fermentation Media
Affects 1.The transport of certain nutrients in and out of cells2.The metabolic functions of cells 3.The solubility of certain nutrients (DO)
The ionic strength is given by the following equation:
C = concentration of an ionZi = charge of ionI = ionic strength of the medium
High substrate concentrations that are significantly above stoichiometric requirements are inhibitory to cellular functions and depending on the type of cells and substrate.
Substrate Concentration (g/L)
1.
Inhibitory concentration
Glucose (yeast fermentation)
200
2. NaCl 40
3. Refractory compunds (phenol, toluene, methanol)
1
4.
Noninhibitory concentration:
Nutrients:AmmoniumPhosphateNitrate
5105
Heat generation by microbial growth
About 40-50% of the energy stored in a carbon and energy source is converted to biological energy (ATP) during aerobic metabolism and the rest of energy is released as heat.
For actively growing cells, the maintanance requirement is low and heat evolution is directly related to growth.
The heat generated during microbial growth can be calculated using the heat of combustion of the substrate and of cellular material.
A schematic of an entalphy balance for microbial utilization of substrate
A schematic of an entalphy balance for microbial utilization of substrate
The heat of combustion of the substrate is equal to the sum of the metabolic heat and the heat of combustion of the cellular material
Hs = Heat of combustion of substrateHs = Heat of combustion of substrate
Hc = Heat of combustion of cellsHc = Heat of combustion of cells
1/Yc = Metabolic heat evolved per gram of cells
1/Yc = Metabolic heat evolved per gram of cells
Traditional Batch Fermentation
Yogurt Soy Sauce @ Kicap
Traditional Fermented Food @Tapai Tempeh
Introduction : Soy Sauce @ Kicap
Soya sauce @ kicap
Salty soy sauce @ kicap asin
Sweetened soy sauce @ kicap manis
FermentationSoya beans
“a liquid food condiment which is used to add flavour and colour to the Oriental diet (Yong and Wood, 1974)
History
invented in China as condiment for ~2500 years
widely used in East & Southeast Asia & in some Western dishes
2 methods : traditional brewing method (fermentation) & non – brewed method (chemical-hydrolyzation)
FLOW CHART FOR SOY SAUCE PRODUCTION
Soy Beans
Pretreatment of soy beans (cleaning, soaking, cooking and draining)
Fungus culture + wheat flour
Mix
Incubated in koji room (48 hours)
KojiBrine solution
Incubate Moromi (2 months)
Extraction Residue
Filtrate
Additives
Packaging
Pasteurization
Soy sauce @ Kicap
Chinese soy sauce
Indonesian soy sauce
Japanese soy sauce @ Shoyu
Yogurt
Yogurt (yoghurt) is a healthy source of protein, calcium, magnesium, and other essential vitamins, whose active bacterial cultures aid in digestion.
Make Your Own… It tastes better It's better for you : no preservatives
no sugar no chemicals added It's less expensive There's no packaging waste
Make your own yogurt…
Add milk
Heat 80°C (10-20 min)Cool rapidly to about 45°C
Pitch your yogurt
Incubate ~ 4 - 18 hours (custardlike)
Stir well
Chill overnight
Stir & ENJOY !!!
Stir, cover, warm
Traditional Fermented Food @ Tapai Origin
Found throughout much of East- and Southeast Asia It is a sweet or sour alcoholic paste Tapai can be made from a variety of carbohydrate
sources Tapai is also used to make alcoholic beverages
Tempeh
Origin Natural culturing and controlled fermentation
process It originated from Indonesia, invented by the
Javanese Made from soybeans Tempeh fermentation process
higher content of protein, dietary fiber and vitamins Tempeh is used worldwide in vegetarian cuisine
How to make Tempeh?
Source: Tempeh Wizard’s Guild
SummaryBatch Culturea large-scale closed system culture in which cells
are grown in a fixed volume of nutrient culture medium under specific environmental conditions (e.g. nutrient type, temperature, pressure, aeration, etc.) up to a certain density in a tank or fermentor, harvested and processed