THE CHANGES INDUCED BY ISOAMYLASE IN THE MOLECULAR-STRUCTURE OF AMYLOPECTINS ISOLATED FROM TROPICAL STARCHES

Four kinds of tropical starches, i.e., edible canna, arrowroot, cassav a and sage were used to study the molecular structure of amylopectins. Potato and corn amylopectins were used as controls. The changes in th e weight average molecular weight M(W), radius of gyration R(G) which is a function of the molecular size and intrinsic viscocity [eta] were determined to establish differences in the debranching reaction induc ed by isoamylase. The weight average molecular weight M(W) and radius of gyration R(G) were monitored by the light scattering method. It was shown that R(G) per M(W) was different among six kinds of amylopectin s as a function of decreasing M(W) (10(8) similar to 10(7)), i.e., cas sava and corn were the highest, potato, edible canna, and arrowroot we re intermediate and sage was the smallest, An addition, the velocity o f the isoamylase alpha-1.6 debranching reaction varied a little among the six kinds of amylopectins. However, the decreasing ratio of R(G):M (W) was almost similar for six kinds of amylopections from observation of almost identical slopes in a log-log plot of R(G) VS M(W). As the debranching reaction proceeded, the plots became non-linear and showed individual specificities. Accordingly, it was postulated that the deb ranching mechanism was the same in relation to M(W) and R(G) among all six amylopectins.