Topics: Enzyme, Chemical reaction, Temperature Pages: 7 (1845 words) Published: April 27, 2014
To investigate the effect of different temperatures on the activity of rennin in milk Introduction
Enzymes are globular protein, responsible for most of the chemical activities of living organisms. They are made up of long chains of amino acids containing carbon, hydrogen, oxygen and nitrogen (Gunsch, 2012). The role of enzyme is to act as catalysts, substances that speed up chemical reactions without being chemically altered during the process. The speeding up of chemical reactions is done by lowering the activation energy required to start a reaction. Enzymes are specific in their actions, and they contain active sites that will temporarily bind to a specific substrate for the bonds in the substrate to be broken and the products to be released. Every enzyme has a set of optimum conditions. Factors like temperature, pH and substrate concentration have an impact on enzyme activity. In this experiment, the enzyme Rennin, a type of proteolytic enzyme that is usually used to coagulate milk to make cheese, was used. Rennin usually serve as protein-digesting enzyme that coagulates milk by transforming soluble caseinogen into insoluble casein in the form of curd like structure (Whitaker, n.d). Rennin can be found in the gastric juice of cud-chewing animal such as cow (Whitaker, n.d). Rennin like every enzyme has a certain temperature range where it can function most efficiently. For rennin, the optimum temperature is around 37 oC – 40 oC in correspondence with the internal mammalian body temperature. The objective of this experiment was to determine the effects of different temperature conditions on the activity and functionality of the enzyme in the enzyme-catalysed reaction. It is expected that the rate of reaction will increase as the temperature increases until it reaches the optimal temperature of 37 oC – 40 oC, then abruptly decline with further increase of temperature. Beyond the optimal temperature, the rate of reaction will begin to slow down and reaction will stop when the temperature reach the certain point where most enzyme will be expected to denature under those conditions.

Materials and Methods
- Equipment
12 test tubes
Water bath incubators
150 ml beaker
Mortar and pestle
Striring rod
10 ml measuring cylinder
- Materials
3 Rennet junket tablets
Dairy Cow’s milk
- Procedure
1. Set up water bath incubators to temperature 25 oC, 37 oC, 40 oC, 50 oC, 60 oC and 80 oC. 2. Rennin enzyme was obtained from dissolving commercial rennet extract (known as junket tablet). Grind up thoroughly 3 junket tablets. Add 10 ml of distilled water to dissolve the rennet. Gently stir the solution. 3. For each temperature point, two test tubes are needed. Fill in each these test tubes with 5 ml of milk, label one as ‘A’ and the other one as ‘B’. 4. Immerse both test tubes into the required temperature of water bath incubator. Allow the milk to reach the required temperature before proceeding. 5. Add 3 drops of diluted rennin to test tube ‘B’ while leave test tube ‘A’ as control. Start the timer and monitor the time when the milk curds start to appear and when it completely coagulates. In the process, tilt the test tube every 15 seconds interval to check the progress of clotting. 6. If clotting does not occur within 10 minutes waiting period, record as no clotting occurring. 7. Repeat step 3 – 6 at the rest temperature points.

8. Perform the second trial of the experiment at each temperature point.

Table 1 – Showing the different time required for milk to coagulate completely under different temperature conditions Table 2 – Observations of the final physical texture of the milk in Test Tube B Temperature (oC)


Trial 1
Trial 2
Solid block formed
Solid block formed
Solid block formed
Solid block formed
Solid block formed
Solid block formed
Thick clumps coagulating the bottom of test tubes, minor traces...

References: Allogio, V, Caponio, F, Pasqualone A & Gomes, T 2000, ‘Effect of heat treatment on the rennet clotting time of goat and cow milk’, Journal of Food Chemistry, vol.70, no.1, pp.51-55, viewed on 26 May 2013, from .
Barker, JR, (n.d), ‘Temperature and Enzyme Activity’, Department of Zoologogy and Comparative Anatomy, Oxford, pp.723-727, viewed on 29 May 2013, from
Bowen, R, 1996, Chymosin (Rennin) and the Coagulation of Milk, accessed 28 May 2013 from .
Gunsch, J, 2012, What are enzymes, viewed on 28 May 2013, from .
John, D (2012), Effect of Temperature on Enzyme Activity, viewed on 29 May 2013, from
Whitaker, E, (n.d.),The Effect of Temperature on the Enzyme Rennin, accessed on 28 May 2012 from .
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