An amylase-producing strain was isolated from soy sauce and designated as Bacillus subtilis ZJ-1. Purification of α-amylase from B. subtilis ZJ-1 to homogeneity by ethanol fractionation, ultrafiltration, and Sephadex G-100 gel filtration resulted in recovery of 8.9% and a specific activity of 542.7 U/mg protein. The molecular mass was estimated to be 58 kD by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The enzyme reached its maximum activity at a pH of 5.0 and a temperature of 50°C. The enzyme remained at 89.4 ± 3.0% of its activity at 40°C. The enzyme retained 87.7 ± 3.7% and 63.4 ± 2.9% of its original activity at 40°C after a 60-min incubation in the presence of 5 mM CaCl2 at a pH of 5.0 and 4.0, respectively. These properties indicate that the novel enzyme has a theoretically high survival rate and excellent starch catalytic efficiency in the typical chicken gastrointestinal-tract environment (pH 3.5-7.0, 40°C). In addition, the enzyme remained at 78.4 ± 3.6% of its activity after a 5-min incubation at 80°C, which demonstrates that the enzyme could maintain a high survival rate in the pelleting process of feed production. The characteristics just described make this enzyme a good candidate for use as a chicken feed enzyme.
Keywords: Bacillus subtilis ZJ-1; acidic α-amylase; feed enzyme; pH stability; thermostability.