THESIS
THESIS
THESIS
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1.3.4 In vitro starch digestibility<br />
116<br />
Pullulanase enzyme concentration (0, 8, 10, 12, 14 and 16 unit/g<br />
starch) dependence of RS III formation was examined, and in vitro starch digestibility<br />
(% dwb) of RS III formation was presented in Figure 28. Resistant starch content<br />
increas ed sharply<br />
as the amount of the enzyme increased to at 12 units/g starch,<br />
reaching highest (19.81 %) resistant starch content. Furthermore, resistant starch<br />
content in RS III samples dramatically decreased to 17.31 % and 13.16 % upon higher<br />
content of the enzyme (14 and 16 units/g starch). Meanwhile, digested starch content<br />
decreased as the resistant starch content increase. The digested starch and total starch<br />
content in the RS III samples range between 74.29 to 90.09 % and 93.24 to 94.40 %,<br />
respectively.<br />
This result indicated that the amount of resistant starch could be<br />
related to the degree of pullulanase hydrolysis. The higher degree of pullulanase<br />
hydrolysis may be attributed to the formation of short linear polymers linked by α-1,<br />
4-glucosidic bonds fractions that<br />
may inhibit rearrangement of granules thereby<br />
preventing retrogradation. As Gidley and Bulpin (1987) suggested, a chain length of<br />
at least<br />
10 glucose units was required for crystallization and, by inference, for the<br />
formation of double helices. On the other hand, short chains with DP 6-9 glucose<br />
units are known to inhibit retrogradation (Levine and Slade 1986, Shi and Seib, 1992).<br />
Gidley et al, (1995) observed that an approximate relative maximum at DP 20 - 30<br />
suitable to form RS III. Eerlingen et al. (1993) found that the chain length of the<br />
resistant regions (DP 19 - 26) was independent of the amylose average chain lengths<br />
originally used to form the RS III.<br />
Many researchers would expect retrogradation to have an<br />
effect on the covalent structure of the native starch granules. Faissant et al. (1993) and<br />
Cairns et al. (1995) revealed that resistant starch obtained from retrograded high<br />
amylose maize starch consisted of three chain populations. The average chain lengths<br />
of these populations depend on the starting materials and enzymatic treatment.<br />
However, in both case a high molecular weight fraction ( DP n > 100), a medium