EXTENSIVE DEGRADATION OF NATIVE STARCH GRANULES BY ALPHA-AMYLASE FROM ASPERGILLUS-FUMIGATUS

Starch granules of various botanical origins were subjected to enzymic degradation by purified alpha-amylases from pig pancreas, Bacillus sp. and Aspergillus fumigatus (Aspergillus sp. K-27). With the A. fumigatus enzyme, glucose in alpha-anomeric configuration was the sole end degradation product regardless of the starch tested. The efficiency of this enzyme was very high on all native starch granules. Starches from normal and waxy maize, smooth pea and wheat were completely solubilised within 30 h using 1.34 nKat/mg of substrate. High-amylose maize, wrinkled pea and potato starches were degraded to lower extents (50, 70 and 45%, respectively). Such high enzymic efficiency was not observed with alpha-amylases from pig pancreas or Bacillus sp. With alpha-amylase from A. fumigatus, normal and waxy maize starches displayed highly eroded layered structures when observed by scanning or transmission electron microscopy during degradation. In contrast, potato and high-amylose maize starches produced a minor fraction of endo-eroded granules, whereas the rest of the granules exhibited superficial porosity.