Molecular characteristics of glucans: High-amylose cornstarch

Macroscopic properties of starch are determined by molecular characteristics such as molecular weight distribution, branching characteristics, glucan coil packing density and coil dimensions. For determination of these characteristics, glucan fractions of high-amylose corn starch have been prepared by selective precipitation. A fraction of 70% mass was fractionated by n-butanol precipitation and is expected to consist of non-branched (nb) and long-chain branched (Icb) glucans. A second fraction of 30% mass was precipitated by an excess of methanol from the prior n-butanol complexation and is expected to consist of short-chain branched (scb) glucans. For analytical purposes the glucans were dissolved in DMSO to get true solutions. These samples were separated on a SEC-system with an aqueous eluent, a procedure which includes an in-line switching of glucan-solvent from DMSO to water. Dual in-line detection of mass and scattering intensity yielded basic data to achieve distributions of sphere-equivalent glucan-coil dimension (R(e)D) and of absolute molecular weights as well in terms of mass (MWD(m)) as of number (MWD(n)) of constituting components. Additional application of enzymatically catalyzed hydrolization of branching linkages yielded the constituting glucan chain distribution and information about chain lengths of branches.