A moderately thermophilic Bacillus subtilis strain, isolated from fresh sheep's milk, produced extracellular thermostable α-amylase. Maximum amylase production was obtained at 40°C in a medium containing low starch concentrations. The enzyme displayed maximal activity at 135°C and pH 6.5 and its thermostability was enhanced in the presence of either calcium or starch. This thermostable α-amylase was used for the hydrolysis of various starches. An ammonium sulphate crude enzyme preparation as well as the cell-free supernatant efficiently degraded the starches tested. The use of the clear supernatant as enzyme source is highly advantageous mainly because it decreases the cost of the hydrolysis. Upon increase of reaction temperature to 70°C, all substrates exhibited higher hydrolysis rates. Potato starch hydrolysis resulted in a higher yield of reducing sugars in comparison to the other starches at all temperatures tested. Soluble and rice starch took, respectively, the second and third position regarding reducing sugars liberation, while the α-amylase studied showed slightly lower affinity for corn starch and oat starch.
- α-Amylase; Production; Bacillus subtilis; Starch; Hydrolysis