The Effect of Changing pH in Yeast Fermentation

1. The Effect of Changing pH in Yeast Fermentation Debbie Sasges Kelsey Sunderland Lauren Rizzo

2. 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.

3. 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.

4. 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.

5. 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.

7. 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.

8. 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.

9. 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.

10. 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?

11. Yeast is Fun!