Aim To investigate why jelly fails to set in the presence of fresh pineapple and kiwifruit. Introduction Last week, Mary prepared some jelly for her mother ’s birthday. In addition to plain jelly, jelly, she added fresh fresh fruits into some of the jelly. jelly. She found that that all the plain jelly could be set as usual, but jelly with fresh pineapple and fresh kiwi added failed to set as the plain jelly. Hypothesis Jelly contains a kind of protein called gelatin, which causes the jelly solution to solidify and set after cooling. Fresh pineapple and kiwifruit contain proteases that are able to break down gelatin, which makes the jelly fail to solidify. Principle Dependent variable: In this experiment, we we examined the solidifi solidification cation of jelly
under the following
different conditions. Independent variable: Jelly that contained fresh pineapple and kiwifruit juice To show that the presence of some kind of substance in fresh pineapple and kiwifruit juice contributes contributes to to the inhibition of of the solidification solidification of the jelly. jelly. It was predicted predicted that the jelly would not be set. Jelly that contained cooked pineapple and kiwifruit juice To test whether it is proteases in the fruit that prevents the gelatin from solidifying. Since enzyme is denature by heat, cooking the pineapple and kiwifruit juice would eliminate the presence of enzyme in the fruit. This is to test whether the jelly fails to solidify because of the enzyme’s breaking down the gelatin in the jelly. If the reaction of enzyme is responsible for preventing the jelly from being set, this set of test would show positive result—the jelly would be set —since the proteases in the fruit were inactivated by heat. Controlled variables: Jelly that did not contain fruit To ensure that the jelly could be set under normal condition and that the result obtained in the test condition — jelly added with with fresh pineapple pineapple and kiwi kiwi —is due to the presence of the fresh fruit and not other extraneous factors, a control
experiment with plain jelly sample was set up. It was predicted that the jelly sample would be set. Jelly that contain meat tenderizer (which contains protease) To testify whether protease could inhibit the solidification of jelly by breaking down gelatin, meat tenderizer—which contains protease—was added to the jelly samples. It was predicted that it would not be solidified. Procedure: 1.
2.
Eighteen boiling tubes were labeled according to the following contents: a.
Plain gelatin: Total of two boiling tube (labels: a1, a2)
b.
Fresh pineapple and kiwifruit: Total of 4 boiling tube (labels: b1, b2, b3, b4)
c.
Cooked pineapple and kiwifruit: Total of 4 boiling tube (labels: c1, c2, c3, c4)
d.
Meat tenderizer : Total of two boiling tube (d1, d2)
The pineapple and kiwifruit were cut into small pieces, mashed into juice and filtered.
3.
Half of the juice of both fruit was boiled in a bubble bath for 5 minutes. The rest of the fruit juice was left raw.
4.
Approximately half of the fruit juice(cooked or raw) were added in to each of the boiling tube that were labeled as containing fruit. (b1,b2 b3, b4, c1, c2, c3, c4)
5.
Two teaspoon of meat tenderizer were mixed with two teaspoon of water until it was dissolved. One teaspoon of the meat tenderizer solution were added into each of the boiling tube. (label: d1, d2)
6.
The jelly was made according to the package instructions. Three cm3 of jelly liquid was added into each of the boiling tube. The content of each boiling tube was stirred thoroughly. Different glass rod was used in stirring different solution.
7.
The boiling tubes were put into the refrigerator for 15-20 minutes. The time at which the jelly was put in was recorded.
8.
The jelly were examined every 5 minutes for their degree of solidification.
Result
Table of the results of different test conditions test conditions
boiling tubes
status of the
status of the
status of the
plain jelly
jelly after
jelly after
jelly after
5 min
10 min
15 min
a1 a2
jelly with fresh
b1 (pineapple)
pineapple and
b2 (pineapple)
kiwifruit
b3 (kiwifruit) b4 (kiwifruit)
jelly with
c1 (pineapple)
cooked
c2 (pineapple)
pineapple and
c3 (kiwifruit)
kiwifruit
c4 (kiwifruit)
jelly with meat
d1
tenderizer
d2
Key: +++ high degree of solidification + low degree of solidification - no solidification Discussion Suggestion: 1. The same amount of jelly liquid and fruit juice should be added to each boiling tube for fair comparison. 2. Each test condition should have two sets to show that the result is repeatable. 3. For further investigation, we can repeat the experiment with different kinds of fruit such as apple, orange, to see whether they have the same effect on the solidification of jelly as pineapple and kiwifruit. 4. We can also tests the effect of different kinds of independent variables, such as frozen fruit, dried fruit, canned fruit, the amount of fruit and the pH of the fruit juice. Limitation: 1. The pH of the fruit juice was not controlled in the experiment. This might affect the activity of the enzyme. 2. The enzyme that broke down the gelatin was not isolated from the fruit. We could not identify the specific kind of enzyme that was responsible for inhibiting the solidification of the jelly.
Conclusion: From the table of result …….it can be seen that
