Abstract
α-Amylase production by thermophilic Bacillus sp strain SMIA-2 cultivated in liquid cultures containing soluble starch as a carbon source and supplemented with 0.05% whey protein and 0.2% peptone reached a maximum activity at 32 h, with levels of 37 U/mL. Studies on the amylase characterization revealed that the optimum temperature of this enzyme was 90°C. The enzyme was stable for 1 h at temperatures ranging from 40-50°C while at 90°C, 66% of its maximum activity was lost. However, in the presence of 5 mM CaCl2, the enzyme was stable at 90°C for 30 min and retained about 58% residual activity after 1 h. The optimum pH of the enzyme was found to be 8.5. After incubation of enzyme for 2 h at pH 9.5 and 11.0 was observed a decrease of about 6.3% and 16.5% of its original activity. At pH 6.0 the enzyme lost about 36% of its original activity. The enzyme was strongly inhibited by Co(2+), Cu(2+) and Ba(2+), but less affected by Mg(2+), Na(+) and K(+). In the presence of 2.0 M NaCl, 63% of amylase activity was retained after 2 h incubation at 45°C. The amylase exhibited more than 70% activity when incubated for 1 h at 50°C with sodium dodecyl sulphate. However, very little residual activity was obtained with sodium hypochlorite and with hydrogen peroxide the enzyme was completely inhibited. The compatibility of Bacillus sp SMIA-2 amylase with certain commercial detergents was shown to be good as the enzyme retained 86%, 85% and 75% of its activity after 20 min incubation at 50°C in the presence of the detergent brands Omo(®), Campeiro(®) and Tide(®), respectively.