Fermentation Lecture 11
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Transcript of Fermentation Lecture 11
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FermentationKinetics of Yeast Growth
and Production
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Introduction
Fermentation can be defined as an energy yielding process where yeastconverts organic molecules (such as sugar) into energy, carbon dioxideor/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 doesnot get as much energy from the substrate. Yeast produces ethanol when itrespires anaerobically and ultimately the ethanol will kill the yeast (find outwhy is yeast continue to produce ethanol even the last is an inhibitor).
C6H1206 2 CH3CH2OH + 2 CO2+ 2 ATPC6H1206+ 6O26CO2+ 6H2O + 16-18 APT
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When the feed substrate to the reactor is notmonosaccharide e.g. sucrose (C12H22O11), yeastenzyme cause glycosidic bond to break in a processcalled hydrolysis
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Industrial and Commercial Applications
Food Industry
~ Beer
~ Bread
~ Cheese
~ Wine
~ Yogurt
Pharmaceutical Industry
~ Insulin
~ Vaccine Adjuvants
Energy
~ Fuel Ethanol
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Objective
To find the kinetics of the system by using
Nonlinear Regression (guess for ks and m) The Sum of the Least Squares and the
Lineweaver-Burk Plot methods in order todetermine the parameters mand ks
To determine the yield coefficient and to
project min. and max. amount yeast cell mass,carbon dioxide and ethanol produced
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Experimental Set Up
Apparatus
Bioreactor
pH meter
Sampling
device
Mixer
Temperature
sensor
YSI 2700
Biochemistry
Analyzer
pH probe
D-oxygen
probe
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Experimental: Procedure
Using Biochemistry Analyzer and Spectrophotometer
to measure and make calibration curves for sugar and
yeast cell concentrations
Reactant initial concentration dextrose/or sucrose 25 g/L
yeast 3 g/L
volume reactant solution 2 L
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Initial conditions & assumptions
Initial Conditions 2 L of solution
50 g sugar
pH around 5.0
Temperature around 28-30C
Assumptionsthe bioreactor content is
well mixed and has a constant medium volume at a certain
initial conditions Temperature is constant
pH maintained at optimal pH of 3.00
All reactants or nutrients present in excess except for sugarsubstrate.
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Theory
In 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 consumption
rx = rate of cell growth
s = substrate concentration
x = cell concentration
P = ethanol concentration (in anaerobic case)
rxCells (x)
P
Cells (x)
rsx
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Theory
The plot showing the trends for yeast cell growth over time
rx =
dCx
dt
rx =
dx
dt
xBiomass
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Lineweaver-Burk Rearrangement
+=
ss
s
ms
sk
s)(mm
s
m
s
s s
k
s
sk
111
)(
+=
+
=
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Nonlinear Regression
1. Define Model
2. Solve for Rpredicted(dx/dt)(calculate dx/dt from the polynomial equation fittedto the curve x(t)
3. Make initial guess for ks and m
(mis the max. specific growth rate can be achievedwhen S >> ks
ks is saturation constant or the value of limitingsubstrate conc. S at which sequal to the half of m
4. Minimize (R-Rpredicted)2 using solver function in
Excel by varying ksand m
+==
ss
s
mxsk
sx
dt
dxr
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Yield Coefficient Determination
Ratio of cell or Ethanol concentration to substrate concentration.
Knowing Yx/s will give you an idea for how much additionalyeast cell mass, on average, is produced for a given amount ofsugar substrate consumed.
As well allowed you to calculate a lower bound on theexperimental stoichiometric coefficient, , and therefore to
calculate ranges for ethanol and CO2production.(Yeast Cell) + C6H12O6 (CO2 + CH3CH2OH) + (Yeast Cells)
ss
xx
ds
dxY
o
o
s
x
==
Yps
=dP
ds=P P0
s0 s
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Error in Lineweaver-Burk
Parameters
Error in ksand mrelative to error in slope and y-intercept of
linear fit
Random Error in y values:
STDEV of slope:
STDEV of y-intercept:
( )
( )2
2
= nyy
s ii
xy
( )
=2
xx
s
s
i
xy
b
( )
=
2
2
xxn
xss
i
i
xya
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Lower Bound on
(stoichiometric coefficient)
(Yeast Cell) + C6H12O6(CO2+ CH3CH2OH) + (Yeast Cells)
Where, theoretically, = 2.
Assume all yeast generated is attributable only to sugarcomplete consumption
Conservation of mass requires that the remaining product be
equimolar amounts CO2and ethanol