Practical 1

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Dr. WASEEM SAFDAR
Assistant Professor
NDBS-NUMS
Biochemistry-II
(Practicals)

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Content

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Scheme
 Total marks = 20
 Practical Demonstration
 Practical Performance (on campus)
 Note Book /Assignments
 Exam (written)
 Viva (on campus)

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Fermentation of sugars
by Baker’s yeast
Principal of Fermentation
Materials
Method
Result
Interpretation
Conclusion

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Principal
 Fermentation is a metabolic process that produces chemical changes
in organic substrates through the action of enzymes.
 The science of fermentation is known as zymology.
 In microbiology, fermentation is the primary means of
producing energy (ATP) by the degradation of organic nutrients such
as carbohydrates, anaerobically
 Carbohydrates are organic molecules that comprise carbon, hydrogen,
and oxygen in the ratio (CH2O)n.
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 Monosaccharides
 Disaccharides
 Polysaccharides
 Microorganism chemically breakdown complex carbohydrates to
simple forms by use of certain enzymes.
 The metabolic end products of a carbohydrate fermentation can be
organic compound and gas (hydrogen or carbon dioxide).
 Sugar fermentation results in the production of ethanol and carbon dioxide.
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The carbohydrates used in this practical are
Sucrose, lactose, and glucose
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 In the case of sucrose, the fermentation reaction is:
 Lactose is also C12H22O11 but the atoms are arranged differently.
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Materials
 Baker’s yeast
 Distilled water/Tap water
 Sucrose / Lactose / Glucose
 Test tubes (with stopper)
 Electrical balance (0.1 g)
 Water bath (35-45 ºC)
 Stirrer
 Measuring cylinder

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Method
 Measure 20 g of the sugar
 Dissolve in 100 mL of water.
 Heat and stir at 40 oC until all sugar is dissolved
 Allow the sugar solutions to cool to room temperature
 Take 50 ml of solution in a test tube
 Add 2.0 g of baker’sYeast in the mixture
 Heat the mixture in water bath (35-45 ºC) for 15 seconds in order
to fully activate the yeast.
 Loose stopper of the test tube to allow carbon dioxide escape.
 Keep the reaction mixture at room temperature for 36 hours
 Measure the weight of the test tube containing reaction mixture in
start and after every four hours

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Results
Time Weight (g) Difference in weight ( g)
initial weight - Current weight
0
4 hr
8 hr
12 hr
16 hr
20 hr
24 hr
28 hr
32 hr
36 hr
 Initial weight =

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Time (hr)
0
0.5
1
1.5
2
2.5
3
0 4 hr 8 hr 12 hr 16 hr 20 hr 24 hr 28 hr 32 hr 36 hr
CO2 (g)

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Interpretation
Figure shows plots of mass loss over time for sucrose, lactose or glucose.
The results show that while sugar readily undergoes mass loss which
indicate release of CO2 from the reaction mixture.
After a certain time, there will be no loss of weight indicating that reaction
reach to its saturation and nu further substrate is available for fermentation.
Further experiments
Is the rate of fermentation depending on the concentration of the sugar?
Is the rate of fermentation depending on the concentration of the yeast?

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Conclusion
The rate of fermentation is dependent on the
concentration of yeast but independent of the
concentration of sugar.

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THANK YOU