47 Effects of amylopectin branch structures on the physical properties of starch.

J. JANE, Y. Y. Chen, K. S. Wong, A. E. McPherson, Y. Song, and S.-H. Yoo. Department of Food Science and Human Nutrition and Center for Crops Utilization Research, Iowa State University, Ames, IA 50011.

Starches from different botanical sources were fractionated to amylose and amylopectin. Branch chain lengths of the amylopectin molecules were analyzed by using a high-performance anion-exchange chromatography system equipped with a post-column enzyme reactor and a pulsed amperometric detector (HPAEC-ENZ-PAD). Locations of branch linkages in amylopectin were determined by analyzing the structure of Naegeli dextrin of each starch. Results showed that starches of the A-type polymorph had shorter branch chains and with branch linkages scattered in both amorphous and crystalline regions; those of the B-type polymorph had longer branch chains with branch linkages located mainly in the amorphous region; and those of the C-type had both very short and very long branch chains with branching structures in between. Amylopectin branch chain length distributions of many starches display a shoulder at DP 18–21 which is in the proximity of the length of the amylopectin crystalline region. Most starches with an obvious and low shoulder display lower gelatinization temperatures. Starches of B-type polymorph, in general, and those containing substantial phosphate monoesters display lower gelatinization temperatures. Starches with amylopectin of long branch chains also result in high pasting temperatures and more resistant to shear thinning.