Effects of Preheated Treatments on Physicochemical Properties of Resistant Starch Type III from Pullulanase Hydrolysis of High Amylose Rice Starch

摘要

In this study, the effects of preheated treatments on physicochemical properties of resistant starch type III formation by pullulanase hydrolysis of High Amylose Rice Starch (HARS) were investigated. A debranching enzyme (Pullulanase, 8 U g super(-1) starch at 55 degree C for 0-48 h) was introduced to modify the amylopectin molecules of 15% (w/w) HARS suspension (32.10%, amylose content) which had been preheated at 95 and 121 degree C for 30 min. Retrogradation gels of debranched starches with different degrees of hydrolysis (0.14 to 3.10%) were then induced at 4 degree C for 16 h. Afterward, one cycle of the freeze-thaw process (-10/30 degree C) was applied to promote syneresis of the retrograded starches. Results show that pullulanase hydrolysis enhanced the degree of syneresis (33.22, 45.27 and 58.91% for non-debranched and debranched starches which had been preheated at 95 and 121 degree C for 48 h, respectively). The debranched starches with higher degree of hydrolysis provided products with higher resistant starch contents. The resistant starch content increased quadrupled with debranching and the freeze-thaw process (4.07 to 10.68% and 5.12 to 19.32% for 0 to 48 h pullulanase hydrolysis of HARS preheated at 95 and 121 degree C, respectively). Results had shown that after debranching and retrogradation, the HARS molecules had rearranged and changed their crystal pattern from A to V-type pattern, as revealed by X-ray diffraction analysis. In vitro starch hydrolysis index of the RS III samples from 0 to 48 h of pullulanase hydrolysis of the HARS which had been preheated at 95 and 121 degree C were reduced from 71.591 to 41.69% and 68.66 to 26.83%, respectively.