Branching ratios of starch via proton nuclear magnetic resonance and their use in determining amylose/amylopectin content: Evidence for three types of amylopectin

The branching (alpha-1,4)/(alpha-1,6) ratio of starch from a number of sources can be quickly and accurately determined by proton nuclear magnetic resonance NMR. This NMR ratio, with standard ratios for isolated amylose and amylopectin, can then be used to determine the amylose/amylopectin content of starches. In the course of determining the amylose/amylopectin content of various starches, it was discovered that two different types of amylopectin standards were required to obtain results comparable to those obtained from iodine-binding amylose determinations. These two types were a waxy amylopectin, with a high level of branching, and a potato amylopectin, with a lower level of branching. A third type of amylopectin, with a still lower level of branching, is apparently present in high amylose cornstarches, leading to the conclusion that starches with higher amylose contents generally contain amylopectin with a lower level of branching. The three amylopectin types are referred to as amylopectin I, II and III, with the higher numeral coinciding with higher branching (alpha-1,4)/(alpha-1,6) ratio, or less branching.