Denaturing of Enzymes by the Acid
Enzyme works at certain optimal PH.A change in the PH can alter the ionization of amino acids group. The change in Amino acids group alters the hydrogen bonding in the protein molecules Forterre (1989). As a result, the molecules changes their shape making it ineffective lowering it activeness. This eventually denatures the enzymes.
Edwin, F.; Sharma, Y.V.; Jagannadham, M.V. (2002) Stabilization of molten globule state of papain by urea. Biochemical and Biophysical Research Communication