α-Amylase is an enzyme (EC 3.2.1.1; systematic name 4-α-D-glucan glucanohydrolase) that hydrolyses α bonds of large, α-linked polysaccharides, such as starch and glycogen, yielding shorter chains thereof, dextrins, and maltose, through the following biochemical process:[2] It is the major form of amylase found in humans and other mammals.

[5] Both starch, the substrate for ptyalin, and the product (short chains of glucose) are able to partially protect it against inactivation by gastric acid.

Ptyalin added to buffer at pH 3.0 underwent complete inactivation in 120 minutes; however, addition of starch at a 0.1% level resulted in 10% of the activity remaining, and similar addition of starch to a 1.0% level resulted in about 40% of the activity remaining at 120 minutes.

Perry and colleagues speculated the increased copy number of the salivary amylase gene may have enhanced survival coincident to a shift to a starchy diet during human evolution.

Pancreatic α-amylase randomly cleaves the α(1-4) glycosidic linkages of amylose to yield dextrin, maltose, or maltotriose.

Salivary α-amylase has been used as a biomarker for stress[10][11] and as a surrogate marker of sympathetic nervous system (SNS) activity[12] that does not require a blood draw.

Increased plasma levels in humans are found in: Total amylase readings of over 10 times the upper limit of normal (ULN) are suggestive of pancreatitis.

α-Amylase activity in grain is measured by, for instance, the Hagberg–Perten Falling Number, a test to assess sprout damages,[13] or the Phadebas method.

The first step in the production of high-fructose corn syrup is the treatment of cornstarch with α-amylase, which cleaves the long starch polymers into shorter chains of oligosaccharides.

α-Amylase has exhibited efficacy in degrading polymicrobial bacterial biofilms by hydrolyzing the α(1→4) glycosidic linkages within the structural, matrix exopolysaccharides of the extracellular polymeric substance (EPS).