The Collaborative International Dictionary of English v.0.48:

ptyalin \pty"a*lin\ (t[imac]"[.a]*l[i^]n), n. [Gr. pty`alon
   spittle. See Ptyalism.] (Physiol. Chem.)
   An unorganized amylolytic ferment, on enzyme, present in
   human mixed saliva and in the saliva of some animals.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ptyalin
    n 1: an amylase secreted in saliva