Molecular structure of unmodified and chemically modified manioc starches

Abstract

Unmodified ( 1) and a modified ( 2, O-2-hydroxypropyl distarch phosphate) manioc starch were hydrolyzed with pullulanase, beta-amylase, and/or amyloglucosidase and the hydrolyzates fractionated on Sephadex G-50. The amylopectin of 1 had one chain of d.p. 45 to 7.5 chains of d.p. 15. Debranching of 2 with pullulanase yielded only one half of the d.p. 15 chains obtained from 1. The further beta-amylolysis of the debranched 2 was incomplete, although all of the debranched d.p. 15 chains were converted into maltose and maltotriose. Beta-amylolysis of 1 and 2 was 61 and 34%, respectively, and hydrolysis by amyloglucosidase was 93 and 49%, respectively. The relative amounts of the chromatographed fractions suggest that about one-half of the d.p. 15 chains of 2 contained no modifying groups. A model depicting the possible sites of 2-hydroxypropyl and/or phosphate groups on the modified manioc amylopectin molecule is presented.