THESIS
THESIS
THESIS
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1.2.9 Hydrolysis index and glycemic index of RS III samples<br />
104<br />
Figure 20 and Table 16, shows the in vitro starch hydrolysis<br />
results, including the estimated parameter of the calculated hydrolysis index and<br />
glycemic index. The hydrolysis kinetic for the RS III samples showed that the<br />
equilibrium concentration (C∝) of the hydrolyzed starch was changed slightly by pre-<br />
heated treatment and debranching time. The debranch of 121 o C pre-heated rice starch<br />
exhibited a lower C∝ than the 75 o C preheated and 95 o C preheated samples that<br />
debranching at 4 to 48 hr.<br />
The kinetic constant (k) of the starch samples tested showed that the<br />
native high amylose rice starch had highest k value, indicating that hydrolysis<br />
occurred most rapidly in the solubillized samples. While, the RS III formation by<br />
retrogradation of 48 h debranching of 121 o C, 75 o C and 95 o C preheated high amylose<br />
rice starch showed lower k value (0.018 to 0.020) than other treatments (0.21 to<br />
0.036). In addition, the commercial resistant starch (Hi-maize) was lowest in kinetic<br />
constant (0.014), this due to its inherent resistance to enzymatic hydrolysis.<br />
The hydrolysis index (HI) of the RS III samples range between<br />
26.83 to 71.59 % (Figure 20). The RS III samples sowed a lower HI value than the<br />
native high amylose rice starch (82.42 %) but higher than commercial resistant starch<br />
(12.84 %). This behavior indicates that the developed RS III samples are resistant to<br />
enzymatic digestion. The decrease in the enzymatic digestion of starch after<br />
retrogradation has been reported by several researchers although the starch type and<br />
storage conditions were not identical to those used here. Gui and Oates (1997) found<br />
that the degree of digestion of retrograded sago starch (40 % gel) rapidly dropped<br />
from 78.3 to 45.4% within 1 hr storage at 5 o C, but extending the storage time to over<br />
6 hr had little influence on the degree of enzymatic digestion. They claimed that the<br />
digestibility of sago starch was highly sensitive to the retrogradation of amylose that<br />
occurred mainly in the early period of storage, whereas amylopectin recrystallization,<br />
which occurs more slowly, had little influence on the enzymatic digestibility. It is<br />
supposed that the amorphous matrix of starch is readily exposed to the digestive