A catalyst is any substance which makes a chemical reaction go faster, without itself being changed. Our enzymes work best at body temperature. Unlike ordinary catalysts, they are specific to one chemical reaction. An ordinary catalyst may be used for several different chemical reactions, but an enzyme only works for one specific reaction.
Human saliva contains an enzyme called amylase.
This enzyme helps to turn starch into a sugar called maltose. When you swallow a mouthful of food, the amylase stops working because it is much too acid in the stomach pH 2. Amyalse works best in neutral or slightly alkaline conditions, i.e. at about pH 7. When your food gets into the small intestine, more amylase is made by the pancreas and this turns the remaining starch into maltose. Glucose is then absorbed into the blood.