Molecular weight heterogeneity in starch amylopectins

The number‐average molecular weight of a corn amylopectin sample is concluded to be approximately 300,000 on basis of both osmotic pressure and reducing group determination. The weight‐average molecular weight of this preparation was previously shown to be approximately 80 × 10 6 . The ratio of M w / M n is in accord with that expected on the basis of an essentially random synthesis of the branched polymer. Further evidence for an extreme heterogeneity in amylopectins in provided by light scattering studies on subfractions prepared by fractional centrifugation. Conclusive evidence for this broad heterogeneity is obtained by ultracentrifugal analysis. The distribution of sedimentation coefficients is shown to be extreme, significant percentages of the polymer having sedimentation constants ranging from almost zero to above 400 Svedberg units. Some observations on the sedimentation behavior of other amylopectins, their β amylase limit dextrins, and corn amylose are given.