1. Yeast growing aerobically on glucose has a cellular yield coefficient Y x/s =
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1. Yeast growing aerobically on glucose has a cellular yield coefficient Yx/s = 0.5g yeast/g glucose. The elemental cell composition of the yeast (% dry cell weight) is as given below:
C: 47%
N: 7.5%
O: 30%
P: 1.5%
H: 6.5%
S: 1%
Mg: 0.5%
Ash: 6%
A growth medium with an initial glucose concentration of 100g/L had all the glucose consumed in the production of yeast. The growth process may be represented by the unbalanced equation:
Calculate:
(i)the total CO2 produced by performing a carbon balance
(ii)the total H2O produced by performing a hydrogen balance
(iii)the additional O2 that must be added to the system by aeration by performing an oxygen balance
(iv)the cellular yield coefficient of the yeast for oxygen added to the culture growing on glucose
1. Yeast growing aerobically on glucose has a cellular yield coefficient Yx/s = 0.5g yeast/g glucose. The elemental cell composition of the yeast (% dry cell weight) is as given below: A growth medium with an initial glucose concentration of 100g/L had all the glucose consumed in the production of yeast. The growth process may be represented by the unbalanced equation: C6H12O6 + O2 - > Cells + CO2 + H2O. Calculate: (i)the total CO2 produced by performing a carbon balance (ii)the total H2O produced by performing a hydrogen balance (iii)the additional O2 that must be added to the system by aeration by performing an oxygen balance (iv)the cellular yield coefficient of the yeast for oxygen added to the culture growing on glucoseExplanation / Answer
cells coefficient = 0.5g/g glucose
cells produced from 100g/L glucose = 0.5 x 100 = 50g/L
Mol. wt. of glucose = 180a.m.u.
Total atomic wt. of carbon in 180a.m.u. of glucose = 12 x 6 = 72a.m.u.
total carbon present in 100g/L glucose = (72/180) x 100 = 40g/L
total hydrogen present in 100g/L glucose = (12/180) x 100 = 6.67g/L
1. Carbon present in CO2 produced by performing carbon balance = Total carbon in the feedstock - Carbon present in the cells = 40g/L - [(50 x 47) / 100]g/L = 40 - 23.5 = 16.5g/L
Molecular weight of CO2 = 40a.m.u.
Atomic wt. of Carbon in 40a.m.u. of CO2 = 12a.m.u.
CO2 produced = (40/12) x 16.5 = 55g/L
2. Hydrogen present in total H2O produced by performing a hydrogen balance = Total hydrogen in the feedstock - hydrogen present in the cells = 6.67 - [(50 x 6.5) / 100] = 6.67 - 3.25 = 3.42g/L
Molecular weight of H2O = 18a.m.u.
Atomic wt. of Carbon in 18a.m.u. of H2O = 2a.m.u.
H2O produced = (18/2) x 3.42 = 30.78g/L
3. Total oxygen present in 100g/L glucose = (96/180) x 100 = 53.33g/L
Total oxygen present in cells = [(50 x 30) / 100] = 15g/L
Total oxygen present in exhausted CO2 = 55 - 16.5 = 38.5g/L
Total oxygen present in exhausted H2O = 30.78 - 3.42 = 27.36g/L
Total additional O2 required = [15 + 38.5 + 27.36] - 53.33 = 27.53g/L
4. cellular yield coefficient of the yeast for oxygen added to the culture = 50 / 27.53 = 1.82g yeast / added oxygen.
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