18.08.2013 Views

THESIS

THESIS

THESIS

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

1.2.8 In vitro starch digestibility of RS III samples<br />

102<br />

Effects of preheated treatments and hydrolysis time on resistant<br />

starch (RS), digested starch (DS), total starch (TS) content, hydrolysis index (HI) and<br />

glycemic index (GI) in native rice starch, RS III sample and commercial control (Himaize,<br />

National Starch) are presented in Table 15 and 16. RS content and GI have<br />

been established as two important indictors of starch digestibility. RS is used as a<br />

predictor of the speed of release of glucose and GI can be predicted through in vitro<br />

starch hydrolysis model (Englyst et al. 1999; Goni et al. 1997). The RS contents in<br />

48-hr hydrolysis of 121 o C preheated rice starch were (19.19 %) highest but not<br />

significant difference (P≤0.05) from the 16 and 24-hr hydrolysis time (17.14 and<br />

18.33%). The RS contents in the 0 to 48 hr hydrolysis of 75 o C and 95 o C preheated<br />

high amylose rice starch ranged from 4.04 to 12.33 % and 4.06 to 9.68 % base on dry<br />

weight, respectively. They were significantly different from the commercial resistant<br />

starch and native high amylose rice starch. The RS content of the commercial resistant<br />

starch (Hi-maize starch) was 48.32 % base on dry weight. RS content in the native<br />

high amylose rice starch was 4.99 % base on dry weight.<br />

Overall comparison indicated that the higher pullulanase<br />

hydrolysis produced the higher RS content as seen in the 48 hr hydrolysis of 121 o C<br />

preheated treatment. The resistant starch content increased by 4 folds with<br />

debranching process (3.37, 4.12 and 19.31 % for native starch, non-debranched<br />

retrograded starch and 48-hr pullulanase debranched starch preheated at 121°C).<br />

These may be attributed to the formation of several smaller molecular weight<br />

fractions from hydrolysis of the starch during debranching, with the different fractions<br />

recrystallization at low temperature cool down. Recrystallization of these smaller<br />

starch fractions may permit an orderly rearrangement of granules thereby preventing<br />

access to α- amylase digestion (Englyst et al. (1992). The DS content was highest in<br />

the 0 hr of hydrolysis in both of 75 o C, 95 o C and 121 o C heated rice starch which was<br />

90.39, 90.21 and 90.75 %, respectively. All RS III samples contained the same<br />

amount (95.04 – 95.87%) of total starch after enzymatically debranched of high<br />

amylose rice starch.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!