3.3. Effect of pH on activity and stability of purified amylase
The optimum pH was measured in a different buffer system as
described previously. The enzyme displayed appropriate activity in
a broad range of pH, from 3 to 11, with maximum activity at a pH
of 5.0. The enzyme achieved 84% of activity in the pH range of 4.5–
6.0, and showed 94% of activity at pH 5.0 which indicated that the
optimum pH for the enzyme could be considered at pH 5.0
(Fig. 3c). In addition, the enzyme was highly stable in the pH range
of 4.0–9.0 and retained approximately 90% of the initial activity
after 1 h incubation at 70 C. The residual activity sharply
decreased at pH values above 10.0, and 30% of the initial activity
of enzyme was recoverable at pH 11 (Fig. 3d). These results are
in agreement with the activity of amylase isolated from finger millet
(Eleusine coracana), where maximum activity was recorded at
pH 5.0, and the residual enzyme activity markedly decreased at
pH values above 10 (Nirmal & Murali Krishna, 2003). It should be
noted that most amylases purified and characterised from different
plant source have displayed an optimum pH above 6.0 (Elarbi et al.,
2009).