THESIS

hydrolysis of the rice starch preheated at 75 o C, 95 o C and 121 o C for 0 to 48-hr were
0.14 to 1.55% and 0.14 to 0.50%, and 0.17 to 3.10%, respectively.
As the reaction time of hydrolysis increased, the degree of
hydrolysis in the 121 o C and 75 o C preheated increased sharply (0.17 to 3.10%, 0.14 to
1.55%) after 2 and 8-hr hydrolysis time, respectively. While, the rice starch preheated
at 95 o C was remain stable after 8-hr incubation. Because of the 95 o C preheated rice
starch slurry was sticky and less free water content that lead to incomplete
gelatinization of starch granules. These results indicated that pullulanase enzyme was
less activity to hydrolyze the limited free water in the starch solution and native rice
starch. For rice starch to be gelatinized and provide an accessible substrate for
pullulanase hydrolysis the gelatinization process must not be restricted. If water is
limiting the amount of gelatinized starch is restricted together with the capacity of
enzyme to hydrolyze the starch (Tester et al. 2004).
Degree of pullulanase hydrolysis (%)
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0.00
75°C
95°C
121°C
0 2 4 8 16 24 48
Hydrolysis time (hr)
Figure 14 Degree of pullulanase hydrolysis of 0 to 48 hr debranched high amylose
rice starch preheated at 75°C , 95°C and 121 o C for 30 min
92