To determine the rapidly digestible starch (RDS), slowly
digestible starch (SDS), and resistant starch (RS) contents in a starch
sample, the addition of amyloglucosidase is often used to convert
hydrolyzates from α-amylase digestion to glucose. The objectives
of this study were to investigate the exact role of amyloglucosidase
in determining the digestibility of starch and to understand the mechanism
of enzymatic actions on starch granules. Four maize starches differing
in amylose content were examined: waxy maize (0.5% amylose), normal
maize (≈27% amylose), and two high-amylose starches (≈57
and ≈71% amylose). Notably, without amyloglucosidase addition,
the RS content increased from 4.3 to 74.3% for waxy maize starch,
29.7 to 76.5% for normal maize starch, 65.8 to 88.0% for starch with
57% amylose, and 68.2 to 90.4% for the starch with 71% amylose. In
the method without α-amylase addition, less RS was produced
than without added amyloglucosidase, except in maize at 71% amylose
content. Scanning electron microscopy (SEM) revealed the digestive
patterns of pinholes with α-amylase and burrowing with amyloglucosidase
as well as the degree of digestion between samples. To understand
the roles of amyloglucosidase and α-amylase in the in vitro
test, multiple analytical techniques including gel permeation chromatography,
SEM, synchrotron wide-angle X-ray diffraction, and small-angle X-ray
scattering were used to determine the molecular and crystalline structure
before and after digestion. Amyloglucosidase has a significant impact
on the SDS and RS contents of granular maize starches.
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