Purification, characterization and application of thermostable amylopullulanase from Streptomyces erumpens MTCC 7317 under submerged fermentation

Abstract

An amylopullulanase (AP) enzyme has a wide range of applications in the food processing and distillery industries, including the conversion of starch to sugars and the production of conversion syrups (maltose and fructose syrups). The aim of our study was to determine the culture parameters for optimum production of AP by Streptomyces erumpens MTCC 7317. We found that a temperature of 50°C, a pH of 7.0 and an incubation period of 48 h achieved optimal enzyme activity (222.5 units of α-amylase and 69.5 units of pullulanase). The use of soluble starch and beef extract as sources of carbon and nitrogen, respectively, resulted in a higher enzyme production than when other carbon (carboxy methyl cellulose, pectin and pullulan) and nitrogen (yeast extract, peptone, casein, ammonium chloride, etc.) sources were used. The purified enzyme (by ammonium sulphate precipitation) had a molecular mass 45.0 kDa, as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. This band was found to have both amylase and pullulanase activities, as confirmed by thin layer chromatography. As the major end products of the starch digest were maltose and, albeit at a lower amount, glucose, we suggest that this enzyme can be considered to be an AP. The AP of S. erumpens was tested for its ability to liquify cassava bagasse and showed 74% conversion efficiency, which is approximately equal to that of Termamyl. © Springer-Verlag and the University of Milan 2011.