Purification and characterization of a thermostable raw starch digesting amylase from a Streptomyces sp. isolated in a milling factory

A raw starch utilizing microbe was isolated from mud in a milling factory. The 16S ribosomal DNA (rDNA) sequencing and morphological properties of the strain indicated that it belongs to the genus Streptomyces. A strongly raw starch digesting amylase was purified from the culture supernatant of the strain by chromatographic procedures. The specific activity of the enzyme was 11.7 U/mg, molecular mass 47 kDa, optimum pH 6.0, and optimum temperature 50 to 60 degrees C. The enzyme showed sufficient activity even at 70 degrees C. It was activated by calcium, cobaltous, and magnesium ions, and inhibited by copper, nickel, zinc, and ferrous ions. It formed maltose mainly from raw and gelatinized starch, and glycogen. No products were formed from glucose, maltose, maltotriose, pullulan, or cyclodextrins (CDs). The enzyme digested raw wheat, rice, and waxy rice starch rapidly, and raw corn, waxy corn, sweet potato, tapioca, and potato starch normally.