The Effect of Changing pH in Yeast Fermentation

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The Effect of Changing pH in Yeast Fermentation

• Debbie Sasges
• Kelsey Sunderland
• Lauren Rizzo

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Experiment

• We studied the anaerobic respiration capabilities
  of yeast with varying pH levels in the glucose
  solutions.
• We wanted to know how acids and bases affect the
  respiration of yeast and what pH would be the
  optimized pH for this reaction.

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What is the Effect of varying the pH level of the
environment on the rate of the reaction
(anaerobic respiration)?

• We wanted to know how acids and bases affect the
  respiration of yeast and what pH would be the
  optimized pH for this reaction. Is optimal pH 7?
• Possibility that pH when increased or decreased
  dramatically will denature the enzyme that helps
  fuel the reaction, and will in effect, decrease
  the rate at which the reaction occurs.

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Methods and Materials

• Original directions were followed, but instead of
  changing glucose concentration, 5 ml of 10
  glucose solutions of pH 4, 7, and 10 were added
  to the 5 ml of yeast.

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Results

• pH 10 had the slowest rate of respiration. The
  graph has a line with a slope of only about
  1unit/min, which means a reaction rate of about
  .007 mL/min.
• pH 7 had a much steeper slope than that of pH 10
  (about 6.75 units/min), with a reaction rate of
  about .44 mL/min
• pH 4 had the steepest slope (about 7.67
  units/min) and was closest to the control trial.
  We believe that pH 4 is the optimal pH level for
  yeast respiration.

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What This Means

• Since the reaction was slower at pH 10 and pH 7
  than it was in the control trial, it is safe to
  estimate that pH 4 is the optimal pH for the
  fermentation of yeast, or that yeast fermentation
  is aided by a more acidic than basic environment.
  
• Higher pH levels may well have aided in the
  denaturing of the enzyme that help yeast to
  ferment.

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What this Means (cont.)

• Supports the hypothesis that the optimal pH would
  have a faster rate of reaction.
• pH 10 and pH 7 in fact slow down the reaction.

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But. . .

• Possible that experimenters mixed pH solutions in
  the wrong way, or made mistakes measuring out
  glucose solutions or yeast, thusly affecting the
  rate of reaction.
• Machine recorder may not be working perfectly.
• Timing was not always exact, some extra time was
  sometimes given.

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For the Future

• Because the experimenters only had access to 3 pH
  levels, possible research could be done on all
  levels of the pH scale. Try working with pH and
  concentration or with pH and enzymes at extremes.
• What exactly is the pH of the original glucose
  solution?

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• Yeast is Fun!