Light scattering investigation of potato amylopectin

Abstract

AbstractLight scattering measurements were made on amylopectin prepared from potato starch by two procedures. Potato starch dispersed in water at 90° and fractionated with mixed pentanols gave an amylopectin I having a weight‐average molecular weight of 36 million. Dispersion of starch by autoclaving at 120°, followed by nitrobenzene precipitation of amylose, yielded an amylopectin II with weight‐average molecular weight of 14 million. No evidence was found for dissociation of these amylopectins into smaller units in aqueous solution at concentrations as low as 10−6 g./ml., at elevated temperatures, or in sodium hydroxide solutions. Aggregation of amylopectin II occurred at potassium chloride concentrations above 5 × 10−4 molar. Marked reduction of molecular weight of amylopectin II resulted from treatment under a high rate of shear in a Waring Blendor. Acetylated II (40% acetyl content) was soluble in nitromethane, chloroform, acetone, dioxane, and acetonitrile. In all these solvents the molecular weight, corrected for acetyl, was close to 10 million. No evidence was found for an increase in reciprocal specific turbidity at low concentration which would parallel reported osmotic pressure results. Polydispersity was demonstrated by ultracentrifugal sedimentation patterns of amylopectin II, and by separation of amylopectin I into a series of fractions ranging from 7 to 73 million in molecular weight.