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Enzyme activities

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F.6B Fiona Chan (2) Biology Laboratory Report Date: 28-10-2004 Title: Enzyme activities Hypothesis: Papaya, pineapple and kiwi fruit contain protease which will digest the milk protein, casein, in the milk agar plate and form a clear zone. The degree of clearness can be used as an indication of protease activity. No clear zone will be found if we use the boiled fruit juice in the experiment since enzyme denature in high temperature(90oC). Aim: To determine which of the juices squeezed from the fruits(papaya, pineapple and kiwi fruit) show the greatest protease activity. Principle of design: The independent variable in this experiment is papaya, pineapple and kiwi fruit. We use a ruler to measure the diameter of the clear zone which is the dependent variable in this experiment. We also do the experiment with distilled water to act as control, thus we can check whether the effects observed are due to enzymes alone. ...read more.


4. The paper discs were dipped into the fruit juices of papaya, pineapple, kiwi fruit and fruit juices of boiled papaya, boiled pineapple, boiled kiwi fruit and water by using a forceps. 5. The paper discs were placed on the milk-agar plate and were evenly distributed. See figure2 6. A marked was put down on the side of the petri dish to indicate the position. 7. The paper discs were labeled on the petri dish as: PA, PIN, KI, bPA, bPIN, bKI and H2O. 8. The petri dishes were incubated in a 35 oC oven for one night. 9. The degree of clearness of the clear zone were compared in the other day. Precautions : We should provide same room condition for the experiment to ensure that no factors other than enzyme can affect the digestion of casein. We should also soak each paper disc with the same amount of fruit juice to get a more accurate result. ...read more.


The experiment with boiled juices and water was act as a control, it can show that the difference of the results are mainly affected by the activity of enzyme in the unboiled juice. The main source of error in this experiment is the amount of fruit juice that each paper discs soaked in may not be the same. More fruit juice sample we added in the milk agar plate, the more larger the clear zone are, thus it is very difficult to compare the enzyme activity of each fruit sample in a very accurate way. There are many factors affecting the enzyme activity such as temperature and pH and more. We usually immerse the pineapple in salt water before we eat it thus the high pH may denature the protease in the pineapple, so we may not get mouth sores if we eat too much of it. Conclusions : Pineapple shows the greatest protease activity followed by kiwi fruit. Papaya shows the lowest protease activity. ...read more.

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