The effect of magnesium ions
in the fermentation of yeast
van Bodegom, M. & Hofstee, A.
Pallas Athene College, Ede, The Netherlands
13 April 2010
Summary
During the anaerobe dissimilation yeast cells produce ethanol. This is a product we want to have
and we want to optimize it’s production. Anaerobe dissimilation is a complex process with lots of
enzyme involved. These can be stimulate in many different ways, one of than is using co-enzymes. In
our experiment we used the magnesium ions as co- enzymes and we watch whether these had an
influence on the amount of ethanol produced by the yeast S. cerevisiae. The fermentation process
was followed by different amounts of MgCl2 ( 0,00 , 0,50 , 1,00 and 1,50 grams). The weight loss was
measured and that is equal to the amount of CO2 that originated . We saw that with magnesium ions
the CO2 release was higher and the optimal amount was 1,00 gram.
Introduction
Yeast is an eukaryote micro-organism
that needs, just like all living creatures,
energy. In living creatures chemical energy is
carried by ATP. There are two different ways
of gaining ATP: aerobe and anaerobe
dissimilation. The second way is for the yeast
less attractive, because the energy production
is less. But for us, as humans, the second way
is attractive, because as a by-product yeast
produces ethanol . The chemical equation of
the anaerobe dissimilation is:
C6H12O6 (s)
ions. One co-enzyme that is essential during
the glycolysis (fig. 1), the part of the anaerobe
dissimilation in which ATP is formed, is a
magnesium ion. Magnesium ions have effect
on Kinases. Kinases are enzymes which can
attach phosphate groups. The attaching of
phosphate groups is essential, because in the
beginning of the glycolysis 2 ATP (adenine
triphosphate) attach (using kinases) one of
their phosphate groups to the glucose, this is
necessary to start the process. Later on in the
process 4 phosphate groups are attached to 4
ADP (adenine diphosphate), this makes 4 ATP.
So the net profit is 2 ATP.
2 CH3CH2OH (l) + 2 CO2 (g)
We want to gain as much ethanol as
possible and want to find the perfect
circumstances for production. Dissimilation is
a complex process with lot of enzymes
involved. We can stimulate enzymes in
different ways: by hormones, factors
(temperature, pH etc.) and by co-enzymes.
Our interest was drawn to co-enzymes. Coenzymes are for instance vitamins or metal
Our inquiry question is: Does
magnesium ions have influence on the
amount of ethanol produced by
Saccharomyces cerevisiae (baker’s yeast) ? If
yes, what is the optimal amount of
magnesium ions?
Our hypothesis is that magnesium ions
do have influence on the amount of ethanol
produced by S. cerevisiae and the optimal
Fig 1. Glycolyse
amount will not be too low or too high. Coenzymes work in low doses and when there is
too much magnesium the osmotic value is
disturbed and the enzyme will be slowed
down.
Experimental design
We want to know the amount of
ethanol produced by S. cerevisiae, because we
want to see whether magnesium ions affects
this amount. It is difficult to measure the
amount of ethanol , because it is mixed
with glucose, water and MgCl2. But we can
measure the amount of CO2, because CO2 is a
gas it will leave the mixture. CO2 is the only
thing leaving the mixture. So when we weight
the bottles after the reaction, the difference
between before and after the chemical
process will be equal to the amount of CO2
that is produced. We can convert this to
moles. This amount of moles is equal to the
amount of moles ethanol, because in the
equation the coefficients of ethanol and
carbon dioxide are equal.
added that amount. Then we had a solution of
18% D-glucose. Secondly we had to label the 8
erlenmeyers of 50 mL each. We labeled the
erlenmeyers with 0 ; 0* ; 0,5 ; 0,5* ; 1,0 ; 1,0* ;
1,5 ; 1,5*. This numbering stands for the
amount of magnesium chloride in grams in the
erlenmeyers. This amount will be introduced
into the erlenmeyers later. First we added the
yeast. The yeast will be introduced in every
erlenmeyer with an amount of 0,2 grams.
Then we added to every Erlenmeyer the
amount of magnesium chloride which written
on every Erlenmeyer. When those two
ingredients had been introduced into the
erlenmeyers, we filled the erlenmeyers almost
to the top with the 18% D-glucose solution.
We didn’t fill them completely to the top as
there had to be some space where the
released CO2 could get out. To prevent that
Experimental approach
First we had to make the 18% Dglucose solution for the experiment. We did
that by getting a beaker of 800 mL and filled it
with 700 mL of water. For 700 mL of water we
needed 18*7 = 126 grams of D-glucose. We
Fig. 2 Opstelling
air could react with the experiment we added
parafilm on top of every erlenmeyer. Because
of that the CO2 could get out and the O2 could
not get in (CO2 weights more than O2). We
weighted every erlenmeyer and then we put
them all in a stove of 37°C for 2 days. During
those 2 days the S. cerevisea could do their
work and CO2 could be produced .
We kept the variables temperature time, the
amount of yeast and the amount of D-glucose
solution constant. The variable that we
changed in every experiment is the amount of
magnesium chloride.
The accuracy of this design isn’t maximal, as
we did every amount of magnesium chloride
only twice. The measuring is done every time
with three decimals, so that is accurate. The
weighting of the amounts that were added to
the erlenmeyers is done with 2 decimals, so
that is less accurate than the measuring.
Amount of
MgCl2
Amount of
CO2
(g)
0
0*
0,5
0,5*
1,0
1,0*
1,5
1,5*
(g)
1,49
1,34
2,43
1,18
3,45
2,84
1,17
1,75
Averaged
amount of
CO2
(g)
1,41
1,80
3,14
1,46
Table 2
Figure 3 shows the average amount of CO2
versus the amount of MgCl2.
Results
After the two days the weight of all the bottles
was less than before.
Table 1 presents the weights of the bottles
with the different amounts of CO2 before and
after the reaction .
Amount of
MgCl2
(g)
0
0*
0,5
0,5*
1,0
1,0*
1,5
1,5*
Weight
before
(g)
109,36
110,67
110,25
109,13
110,88
110,52
110,05
108,53
Weight after
(g)
107,87
109,34
107,82
107,95
107,43
107,69
108,88
106,78
Table 1
Table 2 presents the amount of CO2
originated in each bottle and the average
amount CO2 of the two bottles with the same
amount of MgCl2.
Fig. 3
Conclusion
The weight loss of the bottles indicates that in
all bottles the S. Cerevisiae culture was
producing CO2. As shown in table 1, the CO2
production was higher when we added MgCl2.
So we can conclude that MgCl2 has a positive
effect on the amount of CO2 produced by S.
Cerevisiae. From the amounts MgCl2 we
tested, 1,00 gram gave the highest amount of
CO2. When we added less or more than 1,00
gram, the amount of CO2 was less than with
1,00 gram.
Evaluation
The experimental setup wasn’t accurate
enough, as the difference between de results
of two erlenmeyers with the same amount of
MgCl2 is quite substantial . What wasn’t
accurate either is that each time one amount
of MgCl2 is only measured in two replicas. For
a reliable result, that amount should be
measured at least 4 to 5 times. What wasn’t
that accurate as well is that we spoiled some
of the solution. This says that the parafilm
wasn’t that tight winded on top of the
erlenmeyers, which means that there might
have reacted O2, although the chance isn’t big.
We also used a range of 0 to 1,5 grams of
MgCl2, when we had the results, we could see
that the optimum amount of MgCl2 lies
around the 1,0 gram. Which means that when
we would like to have a more accurate answer
to our inquiry question, we could do this
experiment again with the amounts of MgCl2
lying around the 1,0 gram.
What also could be a further inquiry question
is if we added another co-enzyme, what kind
of effect would that have on the experiment
and if that amount differs much from the
amount of MgCl2. We could go even further
and compare these results with other kind of
co-enzymes than MgCl2, or even add more cofactors at the same time, would the coenzymes still do their work then?
Bibliography
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Biodata