Effective enzymes pH

Effective enzymes pH: Could I have some info on how I do the ph for the jelly for the pineapple prac please—Exploring Human Biological Science Stage 2 Body Works Activity 27 Page 176. I have been asked to make a 3, 5 and 7 and 2 basics.

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Publication Date: 18 March 2016
Asked By: Kelsey Simm
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Effective Enzymes PH

In brief

Using pineapple in a jelly is a good way to observe the effects of an enzyme on the setting of a jelly.

Enzyme activity is dependent on variables such as temperature and pH. Enzymes are generally effective within a small pH range, depending on the specific enzyme. Altering the pH to be outside the working range of an enzyme can lead to changes in the intermolecular bonds, shape and effectiveness of the enzyme[1].

Commercial jelly is made of gelatine, water, sugar and food colouring[2]. Gelatine is produced from the protein collagen, which is the principal constituent of connective tissues and bones in vertebrate animals[3], and is the key component for allowing jelly to set. Jelly will firm and set when prepared following the instructions on the package. The addition of an acid or a base to the jelly during preparation may alter its ability to set.

Fresh, uncooked pineapple contains Bromelain, a proteolytic enzyme which breaks down gelatine destroying its gelling ability. However, tinned pineapple will allow the jelly to set, as the Bromelain is denatured due to the heat used in the canning process. Bromelain activity is optimal at pH 5.5 to 8[4].

Altering the pH of a jelly can have an effect on any enzymes present, as well as the ability of the jelly to set, so it is important to consider this in the design of an activity. The following suggested method treats the pineapple prior to use.

Method for investigating the effect of pH on setting of gelatine

The following method is adapted from Beware the Biology[5]. A site-specific risk assessment should be undertaken before proceeding with this activity.


  • 10 disposal plastic cups
  • 1M hydrochloric acid
  • 1M sodium hydroxide
  • Gelatine—made up as per package for 100mL
  • Fresh pineapple juice
  • pH strips (0–14)
  • water


  • Prepare fresh pineapple juice by running pineapple through a juice extractor or slice and squeeze by hand
  • Label 5 cups for pineapple juice—pH3J, pH5J, pH7J, pH9J, pH11J
  • Label 5 cups for control—pH3C, pH5C, pH7C, pH9C, pH11C
  • Place 3 mL fresh pineapple juice in each cup labelled ‘J’
  • Adjust the pH accordingly with 1M hydrochloric acid or 1M sodium hydroxide. Check the pH with a pH strip.
  • Place 3 mL water in each cup labelled ‘C’
  • Adjust the pH accordingly with 1M hydrochloric acid or 1M sodium hydroxide. Check the pH with a pH strip.
  • Pour 10 mL gelatine into each cup. Mix thoroughly
  • Leave for 30–60 minutes before checking the setting of each cup

The addition of 1M hydrochloric acid or 1M sodium hydroxide will alter the pH of the pineapple juice. Students should see the gelatine NOT set within the optimal range of pH 5.5-8.0 for the Bromelain enzyme when fresh pineapple juice is used because the enzyme is active for those samples.

To prepare acid and base solutions, see Science ASSIST SOP Diluting concentrated hydrochloric acid and Preparing sodium hydroxide solutions.

Additional information

Setting of agar plates provides an explanation of the chemistry on pH and the setting of agar plates.

Enzyme preparation experiments gives further information on the handling of enzymes.


[1] ‘Enzymes’, Chemistry for Royal Society of Chemistry website, http://www.rsc.org/Education/Teachers/Resources/cfb/enzymes.htm (Accessed March 2016)

[2] ‘What exactly is Jell-O made from?’ How Stuff Works website, https://recipes.howstuffworks.com/j-ello.htm (Accessed March 2016)

[3] Gelatin Manufacturers Institute of America. 2012, Gelatin Handbook, GMIA website, http://www.gelatin-gmia.com/gelatinhandbook.html (Updated June 2018)

[4] ‘Pineapple enzyme – Bromelain’, Curenature.com website, http://www.curenature.com/2013/05/pineapple-enzyme-bromelain.html (Accessed April 2016)

[5] ‘The Effects of pH on the enzyme Bromelain’ Beware the Biology blog http://bewarethebiology.blogspot.com.au/2014/02/the-effects-of-ph-on-enzyme-bromelain.html  (Accessed April 2016)

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