The effect of debranching enzyme concentration on physicochemical properties and alpha-amylase hydrolysis rate of resistant starch type III from high amylose rice starch were studied. The pullulanase enzyme (8, 10, 12, 14 and 16 U/g starch) was introduced to modify amylopectin molecules of 15% (w/w) gelatinized rice starches at 55 degrees C for 16 h. The debranched starches with different degrees of hydrolysis (0.14-5.27%), and having 66.60-98.82% beta-amylolysis limit were then induced at 4 degrees C for 16 h, afterward a one cycle of freeze-thaw process (-10/30 degrees C) was applied. The results showed that a pullulanase hydrolysis improved the degree of syneresis (51.64-54.85% from 8 to 16 U/g starch). Resistant starch content increased sharply as the amount of the enzyme increased, reaching the highest (19.81%) for a 12 U/g starch and decreased to 13.16% by 16 U/g starch. alpha-Amylase hydrolysis rate showed that incompletely-debranched had a lower estimated glycemic index than completely debranched rice starches. Microstructure of the selected RS III samples using X-ray diffraction and scanning electron microscopy revealed a crystal pattern change from A- to V-type pattern and formed a coarse honeycomb-like and a filamentous network structure. (C) 2009 Elsevier Ltd. All rights reserved.