for the gelatinized glutinous rice starch to the active site of -
amylase. Increase in Vm suggests the gelatinization of the native
glutinous rice starch makes the crystallites in granule disrupted to
form more amorphous domains, thereby resulting in diffusion of
the gelatinized glutinous rice starch to easily reach the active site
of -amylase (Crapo et al., 1977).
3.2.2. Susceptibility of native and gelatinized starches to
˛-amylase
The hydrolysis kinetics of -amylase on the native and gelatinized
rice starches is shown in Fig. 2A. Gelatinized glutinous rice
was hydrolyzed more rapidly than granular starch at the initial
stage of hydrolysis. The gelatinized glutinous rice starch is more
rapidly hydrolyzed compared to the native glutinous rice starch at
each time point. The native glutinous rice starch displays a linear
gradual increase in hydrolysis with time and reaches a plateau of
63.34% conversion after 120 min; the hydrolysis of native starch
is slower and reaches a plateau of 19.24% after 80 min. This could
be due to the fact that hydrogen bonds between the amorphous
and crystalline regions may have been disrupted during gelatinization,
thereby increasing the accessibility of the starch chains to
-amylase (O’Brien & Wang, 2008).
Fig. 2B presents the fit of first-order kinetics on the native and
gelatinized glutinous rice starches. The digestion rate coefficients
(k) can be obtained from the slope of the first-order kinetics. The
Fi