The enzyme in the mouth that acts on starch is called ptyalin. Ptyalin is an enzyme that breaks down starch, a type of carbohydrate, into simpler sugars. This process starts in the mouth and is an important part of digestion. When we chew food, ptyalin is released and mixes with the starch in the food. This helps to break down the starch into simpler sugars, making it easier for the body to digest and absorb the nutrients.