Starch is a component in many foods. When iodine is added to starch it turns blue. That is why, in the experiment, the solutions in both beakers turn blue. On addition of saliva which contains an amylase, a starch digesting enzyme (chemical compound that catalyses the breakdown of starch); the starch gradually converts to sugar. Once the starch is broken down, the blue colour disappears. It is important to know that the salivary amylase requires an alkaline medium to act.