Presentation on theme: "Fermentation Kinetics of Yeast Growth and Production"— Presentation transcript:
1 Fermentation Kinetics of Yeast Growth and Production
2 IntroductionFermentation can be defined as an energy yielding process where yeast converts organic molecules (such as sugar) into energy, carbon dioxide or/and ethanol depending on the respiration pathway.Yeast can respire in anaerobically and aerobically.However, yeast gets more energy from aerobic respiration, but in the absence of oxygen it can continue to respire anaerobically, though it does not get as much energy from the substrate. Yeast produces ethanol when it respires anaerobically and ultimately the ethanol will kill the yeast (find out why is yeast continue to produce ethanol even the last is an inhibitor).C6H1206 → 2 CH3CH2OH + 2 CO2 + 2 ATPC6H O2 → 6CO2 + 6H2O APT
3 When the feed substrate to the reactor is not monosaccharide e. g When the feed substrate to the reactor is not monosaccharide e.g. sucrose (C12H22O11), yeast enzyme cause glycosidic bond to break in a process called hydrolysis
5 Objective To find the kinetics of the system by using Nonlinear Regression (guess for ks and μm)The Sum of the Least Squares and the Lineweaver-Burk Plot methods in order to determine the parameters µm and ksTo determine the yield coefficient and to project min. and max. amount yeast cell mass, carbon dioxide and ethanol produced
6 Experimental Set Up Apparatus pH probe D-oxygen probe Mixer Temperature sensorBioreactorYSI 2700 Biochemistry AnalyzerpH meterSampling device
7 Experimental: Procedure Using Biochemistry Analyzer and Spectrophotometer to measure and make calibration curves for sugar and yeast cell concentrationsReactant initial concentrationdextrose/or sucrose 25 g/Lyeast 3 g/Lvolume reactant solution 2 L
8 Initial conditions & assumptions 2 L of solution50 g sugarpH around 5.0Temperature around 28-30°CAssumptionsthe bioreactor content iswell mixed and has a constant medium volume at a certain initial conditionsTemperature is constantpH maintained at optimal pH of 3.00All reactants or nutrients present in excess except for sugar substrate.
9 TheoryIn ideal fermentation process in which the growing cells are consuming the substrate (sugars), and producing more cells according to the following scheme.rsx = rate of substrate consumptionrx = rate of cell growths = substrate concentrationx = cell concentrationP = ethanol concentration (in anaerobic case)rsxrxCells (x)PCells (x)
10 Theory The plot showing the trends for yeast cell growth over time x BiomassThe plot showing the trends for yeast cell growth over time
11 Theory continue Yeast Growth occurs in 4 stages Lag phase, yeast mature and acclimate to environment (no growth occurs)The exponential growth section, the rate of reaction follows first order kineticsDuring the deceleration phase, a large number of parameters, each with saturation effects, have an effect on the kinetics of yeast growth (such as substrate and waste concentrations)The growth rate is ruled by the limiting substrate concentration (sugar)The final equation, often referred to as the Monod equation, looks very similar to the Michaelis-Menten equation.Stationary phase, no growth occurs due to high waste concentration or compleate substrate consumingks = the Monod constant (g/L)μm = a maximum specific growth reaction rate (min-1)
13 Nonlinear Regression Define Model Solve for Rpredicted (dx/dt) (calculate dx/dt from the polynomial equation fitted to the curve x(t)Make initial guess for ks and μm(µm is the max. specific growth rate can be achieved when S >> ks ks is saturation constant or the value of limiting substrate conc. S at which µs equal to the half of µmMinimize Σ(R-Rpredicted)2 using solver function in Excel by varying ks and μm
14 Yield Coefficient Determination Ratio of cell or Ethanol concentration to substrate concentration.Knowing Yx/s will give you an idea for how much additional yeast cell mass, on average, is produced for a given amount of sugar substrate consumed.As well allowed you to calculate a lower bound on the experimental stoichiometric coefficient, γ, and therefore to calculate ranges for ethanol and CO2 production.(Yeast Cell) + C6H12O6 → γ (CO2 + CH3CH2OH) + (Yeast Cells)
15 Error in Lineweaver-Burk Parameters Error in ks and μm relative to error in slope and y-intercept of linear fitRandom Error in y values:STDEV of slope:STDEV of y-intercept:
16 Lower Bound on γ (stoichiometric coefficient) Assume all yeast generated is attributable only to sugar complete consumptionConservation of mass requires that the remaining product be equimolar amounts CO2 and ethanol(Yeast Cell) + C6H12O6 → ϒ (CO2 + CH3CH2OH) + (Yeast Cells)Where, theoretically, ϒ = 2.