Digestion in the Mouth When food is chewed and mixed with saliva, it turns into a moist ball called a bolus. There are three pairs of salivary glands that release saliva. Humans produce approximately 1.5 liters of saliva/day.

Most food undergoes mechanical digestion in the mouth. Only starch is acted on chemically in the mouth. Salivary amylase, a digestive enzyme, begins the chemical process by which starch is changed to simple sugar.

The goal of salivary amylase is to break down large chains of starch molecules into simple sugars that can be absorbed into the bloodstream through the walls of the small intestine. The breakdown of starch cannot be completed in the mouth. Why not?

Why do you think the bolus, at the time it is swallowed, would test positive for both starch and sugar? Proteins and fats may undergo mechanical digestion in the mouth, but they are not chemically changed.