The response surfaces obtained from the empirical
models (2) and (3) are depicted in Fig. 3. Optimal amylase
activity was at pH 4.95 (coded value of 0.22) and
50 C (coded value of 0), with visible decrease toward
low or high values of both variables (Fig. 3). However,
the maximal protease activity was obtained at pH 3.87
(coded value of 0.65) and 53.4 C (coded value of
0.22).
At optimal conditions both enzymes retained approximately
85% of initial activities after 1 h of incubation.
Nevertheless, when the amylase and protease samples
were adjusted for optimum pH value but incubated at
70, 90 and 100 C, their initial activities were completely
lost at 30, 22 and 18 min, respectively (Fig. 4).