Tuesday, February 18, 2014

The Effects of pH on the Enzyme Bromelain (lab report)

The Effects of pH on the Enzyme Bromelain
In this lab, we tested the effects of pH on the enzyme bromelain by altering the pH of liquid jello samples and then added fresh pineapple juice for the bromelain. If the jello set, the enzyme was inactive. If the jello was still liquid, the enzyme was active, breaking down the gelatin in the jello and preventing it from setting. Our results concluded that bromelain does not function in very acidic or basic conditions and functions in more neutral pH levels.
This lab focused on how pH levels affect the function of enzymes. To test this, we used the enzyme bromelain in fresh pineapple juice. An enzyme is activated by a substrate, which fits into a small part of the enzyme. In pineapples, bromelain affects the collagen in the small intestine and prevents the intestine from absorbing the nutrients of the pineapple seed. (Scheve, 2008)  Bromelain also affects gelatin, which is in the jello we used in the lab. If added to the jello, the bromelain in pineapples will prevent the jello from setting. However, different circumstances can prevent the enzyme from catalyzing. Acids and bases can prevent the enzyme from performing its function. If the pH level of the jello is too acidic or too basic, then the enzyme will not function.

  • 4 petri plates
  • some graduated cylinders
  • 4 beakers
  • 6.67g of jello powder
  • 39 ml of cold water
  • 39 ml of warm water
  • 4 ml of pineapple juice
  • pH tester strips
  • one pipet (for the pineapple juice)
  • HCl
  • NaOH
  1. Pour 6.67g of jello powder into the beaker
  2. Add 39 ml of hot water to the jello powder
  3. Stir until dissolved (approximately 2 minutes)
  4. Add 39 ml of cold water to the jello
  5. Stir the jello
  6. Split the total amount of jello liquid into equal portions in four beakers. Use the graduated cylinders to help measure equal amounts.
  7. Pour each individual beaker into its respective petri dish.
  8. Test the pH of the jello without any added acid or base. This is the control.
  9. Change three of the petri dishes to your desired pH level by adding either HCl or NaOH
  10. Measure pH level
  11. Add 1ml of fresh pineapple juice to each petri dish.
  12. Wait for results.

pH level of jello
pH 8
didn’t set
pH 12
pH 1
didn’t set
pH 4 (control)
didn’t set

According to our results, the more neutral and acidic pH levels do not inhibit bromelain from breaking down gelatin while basic pH levels inhibit bromelain function.
If our results were accurate, that would mean our initial hypothesis is false. However, bromelain does not function in conditions that are too acidic or too basic and due to errors such as misinterpretation of directions, pH 1 did not set when it should have. (Quick) The bromelain prevented pH 8 and pH 4 (control) to set because the pH levels were still suitable for enzyme function. So the original hypothesis stands true. Bromelain does not function in conditions that are too acidic or too basic.  Some errors performed during the lab was when we added cold water before stirring the jello. Some spilling of the jello occurred also. Two constants in the lab were the amount of pineapple juice added to the jello and the amount of water in the jello.  In conclusion, bromelain function is inhibited when conditions are too acidic or basic. The enzyme performs its function in more neutral pH conditions.



  1. Thank you for this! It helped a lot! Also I like the format of this.

  2. We combine different advanced techniques, including bioinformatics tools, high-throughput techniques, separation and isolation, discovery of enzymes

  3. how many drops of NaOH did you use to change the pH levels?