Theory & Procedure, Action of Salivary Amylase on Starch | Additional Study Material for NEET PDF Download

Our Objective

Our aim is to study the effect of different temperatures and pH on the activity of salivary content, amylase on starch.

Theory

All living beings need energy to survive. It is from the food we consume that we get our energy. We know that the energy we are getting is by the process of digestion that breaks down the complex substance of starch into simpler molecules of glucose, which are further metabolized into CO₂ and water through the process of glycolysis. The human digestive tract starts at the mouth and ends at the anus.

In the Beginning

The digestion of the food starts as soon as we put food in our mouth. Our teeth cut the food into small pieces and the salivary glands secrete saliva that mixes with these food materials. The saliva contains an enzyme called salivary amylase which hydrolyses starch into maltose. The complete digestion of starch occurs only in the small intestine by the action of pancreatic amylase.

The activity of enzymes is strongly affected by several factors, such as temperature and pH.

Effect of Temperature

All enzymes are proteinaceous in nature. At a lower temperature, the enzyme salivary amylase is deactivated and at the higher temperature, the enzyme is denaturated. Therefore, more time will be taken by an enzyme to digest the starch at lower and higher temperatures. Optimum temperature for the enzymatic activity of salivary amylase ranges from 32 °C to 37 °C. The optimum temperature means that the temperature at which the enzyme shows the maximum activity.  At this optimum temperature, the enzyme is most active and hence, takes less time to digest the starch.

Effect of pH

The optimum pH for the enzymatic activity of salivary amylase ranges from 6 to 7. Above and below this range, the reaction rate reduces as enzymes get denaturated. The enzyme salivary amylase is most active at pH 6.8.  Our stomach has high level of acidity which causes the salivary amylase to denature and change its shape. So the salivary amylase does not function once it enters the stomach.

How to test it?

The effect of temperature and pH on the activity of salivary amylase on starch can be studied by using the Iodine test.  If we add saliva on starch, the salivary amylase present in saliva gradually acts on starch and converts it into maltose.  Starch keeps on giving blue colour with iodine till it is completely digested into maltose.  At this point, no blue colour is formed.  This is the end point or achromic point.

Learning Outcomes:

• Students understand the process of digestion of starch by salivary amylase.
• Students understand the effect of temperature and pH on the activity of salivary amylase on starch.
• Students do the experiment better in the real lab having gone through the animation and simulation.

Effect of Different Temperatures on the Activity of Salivary Amylase on Starch

Materials Required

Three series of test tubes having iodine solution in each, test tubes, ice cubes, water, 15 ml 1% starch solution + 3 ml 1% NaCl, saliva solution, droppers, thermometer, Bunsen burner and wire gauze.

Real Lab Procedure

• Take beaker containing 15 ml of 1% starch solution + 3 ml of 1% NaCl solution.
• Divide and pour this solution into three test tubes and mark them as A, B and C.
• Maintain the temperature of the beaker containing ice cubes at 5°C.
• Take beaker containing ice cubes and keep it on the table.
• Take another two beakers containing water and heat over the Bunsen burner.
• Now transfer experimental tube A into a beaker containing ice.
• Transfer the second experimental tube B into water bath set at 37°C and third experimental tube C into the beaker maintained at 50°C.
• Using a dropper, take 1 ml saliva solution and transfer the solution into test tube A.
• Similarly, add 1 ml saliva solution into test tube B and test tube C.
• Immediately, using a dropper, take few drops from experimental tube A and transfer this into first series of test tubes having iodine solution.
• Similarly, using fresh droppers, do the same procedure for test tube B and test tube C and transfer the solution into second and third series of test tubes having iodine solution.
• Note this time as zero minute reading.
• After an interval of 2 minutes, again take a few drops from each tube and add to the iodine tubes and note the change in colour of iodine.
• Keep on repeating the experiment at an interval of every 2 minutes till colour of iodine does not change.

Results

It takes less time to reach achromic point at 37°C, as the enzyme is maximum active at this temperature, while at higher and lower temperatures more time is taken to reach the achromic point.

Conclusion

All enzymes are proteinaceous in nature. At lower temperatures, the enzyme salivary amylase is deactivated and at higher temperatures, the enzyme is denaturated. Therefore, more time will be taken by enzyme to digest the starch at lower and higher temperatures. At 37° C, the enzyme is most active, hence, takes less time to digest the starch.

Effect of Different pH on the Activity of Salivary Amylase on Starch

Materials Required

Three series of test tubes having iodine solution in each, test tubes, pH tablets of 5, 6.8 and 8, beaker containing water with thermometer, 15 ml 1% starch solution + 3 ml 1% NaCl, saliva solution, droppers, Bunsen burner and wire gauze.

Real Lab Procedure

• Take a beaker containing 15 ml of 1% starch solution + 3 ml of 1% NaCl solution.
• Divide and pour this solution into three test tubes and mark them as A, B and C.
• Add pH tablet 5 into test tube A, pH tablet 6.8 into test tube B and pH tablet 8 into test tube C.
• Now transfer experimental tube A, B and C into a beaker containing water and a thermometer for recording temperature. Temperature of this beaker is to be maintained at 37°C.
• Using a dropper, take 3 ml saliva solution and add 1 ml of solution to each of the three test tubes.
• Immediately using a dropper, take few drops from experimental tube A and transfer this into the first series of test tubes having iodine solution.
• Similarly, do the same procedure for test tube B and test tube C and transfer the solution into second and third series of test tubes having iodine solution.
• Note this time as zero minute reading.
• After an interval of 2 minutes, again take a drop from each tube and add to the iodine tubes and note the change in colour of iodine.
• Keep on repeating the experiment at an interval of every 2 minutes till colour of iodine does not change.

Results

pH 5 is acidic and pH 8 is alkaline, therefore salivary amylase did not act in these tubes. Whereas, the enzyme acted in the tube with pH 6.8 (i.e., slightly acidic) and digested the starch.

Simulator Procedure (as performed through the Online Labs)

• You can select the type of test from the ‘Select the test:’ drop down list (Temperature Test and pH Test).
• You can select the temperature from the ‘Select the temperature:’ drop down list or pH from the ‘Select the pH’ drop down list.
• Click and drag the dropper from the saliva solution bottle and move it into the test tube containing starch solution to drop the saliva solution into it.
• Click and drag the dropper from the stand and move into the solution in the test tube containing starch and saliva solution to collect the sample.
• Still holding the dropper, move it towards test tube that contains iodine solution to drop the mixture into it.
• Consider time adding as zero minute reading. Reading will show below the test tube.
• After an interval of time, again take a drop from the solution and pour into the next test tube containing iodine solution.
• Note the change in colour of iodine.
• Keep on repeating the procedure after a regular interval of time till the colour of iodine does not change.
• You can redo the experiment by clicking on the ‘Reset’ button.

Note: If we add saliva on starch, the salivary amylase present in saliva gradually acts on starch and converts it into maltose.  Starch keeps on giving blue colour with iodine till it is completely digested into maltose.  At this point, no blue colour is formed.  This is the end point or achromic point.