In the first case when we iodine solution is added to the boiled rice, a colour change is observed. The colour becomes blue black because of the presence of starch in the boiled rice. But in the second case when the rice is boiled and chewed, after the addition of iodine solution to it, the color do not change because of the activity of salivary amylase on starch. The salivary amylase converts the starch into maltose and hence it gives a negative test for starch.
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