According to an article published in the Journal of Digestive Diseases and Sciences, salivary amylase is inactivated by gastric acid in the stomach due to acidic pH conditions. Ptyalin, or salivary amylase, is an enzyme secreted by the salivary glands and is found in the mouth.
Salivary amylase begins chemical digestion by breaking down the long-chain polysaccharides from food into smaller maltose compounds. According to Salimetrics, salivary amylase secretion greatly increases in response to taste or the chewing motions of the jaw. Salivary amylase also serves an anti-bacterial purpose in the mouth, so it is present even while not eating.