The action of some α-amylases on starch granules

Abstract

[alpha]-Amylases from human saliva, pig pancreas, Bacillus subtilis and Aspergillus oryzae, and [beta]-amylase from sweet potatoes, were examined for their action on starch granules. Salivary [alpha]-amylase rapidly degraded maize-starch granules. The starch-granule-degrading activity relative to the hydrolysis of dissolved starch varied according to the pH and temperature of the reaction. Adsorption of salivary a-amylase occurred on the surface of starch granules. The extent of adsorption increased at low temperature and high pH; if conditions of temperature and pH were chosen whereby adsorption of the enzyme was decreased, the rate of hydrolysis of starch granules was increased. The efficiency of adsorption was proportional to the surface area of the starch granules and the adsorption obeyed the Freundlich adsorption equation. Pig pancreatic [alpha]-amylase behaved in a similar manner to salivary flamylase in its hydrolytic action on raw starch and in its adsorption on starch granules. Bacillus subtilis [alpha]-amylase hydrolysed maize-starch granules slowly; this amylase was adsorbed on the granules at 0[degree] but not at 35[degree]. Aspergillus oryzae [alpha]-amylase and sweet-potato [beta]-amylase did not degrade maize-starch granules; these amylases were not adsorbed on starch granules under any of the conditions tested. Each crystalline [alpha]-amylase had the same ability to hydrolyse starch granules as the crude source of a-amylase from which it was prepared. It was concluded that certain a-amylases could degrade raw-maize starch and that no special raw-starch enzyme was necessary. None of the amylases studied could degrade potato-starch granules.