The Collaborative International Dictionary of English v.0.48:

Acidulent \A*cid"u*lent\, a.
   Having an acid quality; sour; acidulous. "With anxious,
   acidulent face." --Carlyle.
   [1913 Webster]

WordNet (r) 3.0 (2006):

acidulent
    adj 1: being sour to the taste [syn: acidic, acid,
           acidulent, acidulous]