To Study the Digestion of Starch by Salivary Amylase and Effect of pH and Temperature on it
Every health book insists on the chewing of food. The act of chewing stimulates the excretion of saliva. Saliva mixes up with the food and helps its digestion. That is, the enzyme ptyalin or amylase present in human saliva hydrolyse the big molecules of food into many molecules. For example starch into mono-saccharides maltose and glucose; proteins into amino acids and fats into fatty acids and glycerol. Thus saliva not only helps in digestion of food but convert it into energy generating substances. Further, enzymes and their activity are very sensitive to temperature and pH. Even a slight variation in these two factors, can disrupt the action of enzymes. In other words, digestion of food by salivary amylase is also effected by pH and temperature and can be verified experimentally. For example, hydrolysis of starch can be verified by testing it with iodine solution. Starch forms blue coloured complex with iodine. If no starch is present in a system it will not give blue colour with iodine.
• Test tubes
• Test tube stand
• One dropper
• Stop watch
• Starch and Iodine solution
• Dil. HCl and Dil NaOH solution
Chemistry Experiment Procedure
1) Collection of Saliva - Rinse mouth throughly with cold water and ensure that it does not contain any food particles. Now take about 20ml of lupe warm water in the mouth and gangle for about three minutes so that saliva mixes up well with it. Spit this into a beaker. Filter, if there is any suspended impurity clear filtrate is saliva solution and contains enzyme ptyalin.
2) Preparation of starch solution - Take about 0.5g of starch in a 100ml beaker and add enough water to make a paste. Dilute the paste by adding 50ml water and boil for about 5 min.
3) Digestion of starch
a) take 5ml of the starch solution in a test tube. Add 2 ml of saliva solution into it. Mix the solutions well by shaking the tube carefully and start a step watch.
b) After one minute take out two drops of the mixture solution from the test tube with the help of a dropper and transfer it into another test tube containing about one ml of 1% iodine solution. Note the colour produced, if any.
c) Repeat this test after every one minute taking two drops of the mixture solution and fresh 1% iodine solution continue until the test shows no blue colour. Record the time and blue colour intensity
Absence of blue colour on addition to iodine solution means absence of starch in the mixture solution. That is whole of the starch has got digested or hydrolysed.
Temperature effects the digestion of starch by saliva with increase in temp salivary analyse get inactivated and process of digestion do not take place
Sarawathi lab manual chemistry – XII
Comprehensive lab manual chemistry