Question

Elaborate on the study of digestion of starch by salivary amylase and the effect of ${\text{pH}}$ on it?

Answer 1

Every health book insists on the chewing of food. The act of chewing stimulates the secretion of saliva. Saliva mixes up with the food and helps its digestion.
digestion of food by salivary amylase is also affected by ${\text{pH}}$ and temperature and can be verified experimentally.

Complete step by step answer:
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 converts it into energy generating substances. Further, enzymes and their activity are very sensitive to temperature and ${\text{pH}}$. Even a slight variation in these two factors, can disrupt the action of enzymes. The digestion of food by salivary amylase is also affected by ${\text{pH}}$ and temperature and can be verified experimentally. hydrolysis of starch can be verified by testing it with iodine solution. Starch forms a blue coloured complex with iodine. If no starch is present in a system it will not give blue colour with iodine.
It can be verified experimentally as:
Preparation of starch solution - Take about ${\text{0}}{\text{.5 g}}$ of starch in a ${\text{100 ml}}$ beaker and add enough water to make a paste. Dilute the paste by adding ${\text{50 ml}}$ water and boil for about 5 minutes.
Take starch solution. Add saliva solution. Test the solution with iodine every one minute.

Effect of ${\text{pH}}$ on digestion:
1. Take 3 test tubes with ${\text{2 ml}}$ starch solution and label them. Add ${\text{1 ml}}$ of saliva solution to each tube. Add 1 ml each of water, ${\text{NaOH}}$ solution, and ${\text{dil}}{\text{.HCl}}$ solution to the respective tubes.
2. After a few minutes, a few drops of iodine solution is added to each tube
If we test for the result, it will be observed that The activity of salivary amylase is the best at ${\text{pH}}$ of 6−7 with the highest at a ${\text{pH}}$ of 6.8. So, it means that the activity of salivary amylase is good under acidic to neutral conditions. So, the blue colour will be more in the tube with the ${\text{NaOH}}$ as there will be no activity of the salivary amylase on the starch solution. The blue colour will be light in the tube with water and a very little in the tube with ${\text{dil}}{\text{.HCl}}$ however, it will fade away soon and there will be no colour. This is because the salivary amylase is active in acidic ${\text{pH}}$ and so it will break down the starch to smaller glucose molecules

Note:
The activity of salivary amylase is maximum at a temperature of $32 - 37^\circ C$. At high temperature, the enzyme gets denatured and at lower temperatures, the enzyme is not active, so the enzyme activity does not occur.