Starch Update 2007: the 4 th International Conference on Starch Technology 245 P-STARCH-12 Improvement of Resistant Starch Type III Formation from High Amylose Rice Starch by Enzymatically Debranching Process Jirapa Pongjanta 1 , Anchanee Utaipatanacheep 2 , Onanong Naivikul 3 and Kuakoon Piyachomkwan 4 1 LARTC, Lanna Rajamangala University of Technology, Lampang 52000, Thailand 2 Faculty of Agriculture, Kasetsart University, Bangkok 10900, Thailand. 3 Faculty of Agro-Industry, Kasetsart University, Bangkok 10900, Thailand. National Center for Genetic Engineering and Biotechnology, Bangkok 10900, Thailand Abstract The use of starch as nutrition-valued food products is of great interest among starch industries as Rapidly Digestible Starch (RDS), Slowly Digestible Starch (SDS) and Resistant Starch (RS). Resistant starch can be found in nature of which the contents are varied by botanical source and starch granular structure (i.e. resistant starch type I and II). In addition, resistant starch can be produced from retrogradation of gelatinized starch which is resistant starch type III (RS III). The extents of RS III of most starches are, however, quite low, depending on the molecular structure of starch glucans, namely amylose and amylopectin. In this work, a debranching enzyme (Pullulanase, EC. 232-983-9P, 8U/g starch at 55qC for 0 to 48-hr) was introduced to modify the amylopectin molecules of high amylose rice starches (32.10%, amylose content) which were partially gelatinized at different temperatures (75, 95 and 121qC for 30-min). The retrogradations of debranched starches with different degrees of hydrolysis (0.14 to 3.10%) were then induced at 4qC for 16 hrs. Afterwards, the freeze-thaw cycle (-10/30qC) was further applied to promote synersis of retrograded starches. It was obvious that by a pullulanase hydrolysis improved the degree of syneresis (33.22, 51.45, 45.27 and 58.91% for non-debranched and debranched starches preheated at 75, 95 and 121qC for 48-hr). The debranched starches with higher degrees of syneresis provided products with higher resistant starch contents which were evaluated by pancreatic D-amylase and glucoamylase at 37qC for 16-hr. The resistant starch content increased by 4 folds with debranching process (5.61, 4.12 and 19.31% for native starch, non-debranched retrograded starch and 48-hr pullulanase debranched starch preheated at 121qC). It is undoubtedly that debranching allowed more rearrangement of linear glucans and more ordered structures of retrograded starches which were characterized as V-type, could be obtained as indicated by X-ray diffraction analysis. Keywords: Resistant starch type III, Enzymatically-debranched, High amylose rice starch Introduction Rice, being one of the primary dietary sources of carbohydrates worldwide, is of particular interest when assessing variability in starch digestibility. Miller et al., (1992) classified rice as a high glycemic index food with value ranging from 64 to 93 in the freshly cooked form. The freshly cooked rice contains a lower percentage of RS(below 3%) and tends to increase with amylose content and gelatinized temperature (Walter et al., 2005). The cooling and storing of cooked rice is known to entail starch retrogradation, thus increasing the level of enzyme-resistant starch through recrystallization (Englyst et al., 1999). Thus, resistant starch formations from rice starch are excellent functional food ingredients in regulating glucose control for diabetic patients.