The Changes Induced by Isoamylase in the Molecular Structure of Amylopectins Isolated from Tropical Starches

Abstract

Four kinds of tropical starches, i.e., edible canna, arrowroot, cassava and sago were used to study the molecular structure of amylopectins. Potato and corn amylopectins were used as controls. The changes in the weight average molecular weight Mw, radius of gyration Rg which is a function of the molecular size and intrinsic viscocity [ŋ] were determined to establish differences in the debranching reaction induced by isoamylase. The weight average molecular weight Mw and radius of gyration Rg were monitored by the light scattering method. It was shown that Rg per Mw was different among six kinds of amylopectins as a function of decreasing Mw(108—107), i.e., cassava and corn were the highest, potato, edible canna, and arrowroot were intermediate and sago was the smallest. An addition, the velocity of the isoamylase α-1 • 6 debranching reaction varied a little among the six kinds of amylopectins. However, the decreasing ratio of RG: Mwwas almost similar for six kinds of amylopections from observation of almost identical slopes in a log-log plot of Rc vs Mw-As the debranching reaction proceeded, the plots became non-linear and showed individual specificities. Accordingly, it was postulated that the debranching mechanism was the same in relation to Mw and RgAmongall six amylopectins. © 1995, Japanese Society for Food Science and Technology. All rights reserved.