Branching ratios of starch via proton nuclear magnetic resonance and theiruse 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 sour ces can be quickly and accurately determined by proton nuclear magnetic res onance NMR. This NMR ratio, with standard ratios for isolated amylose and a mylopectin, can then be used to determine the amylose/amylopectin content o f starches. In the course of determining the amylose/amylopectin content of various starches, it was discovered that two different types of amylopecti n standards were required to obtain results comparable to those obtained fr om iodine-binding amylose determinations. These two types were a waxy amylo pectin, with a high level of branching, and a potato amylopectin, with a lo wer level of branching. A third type of amylopectin, with a still lower lev el of branching, is apparently present in high amylose cornstarches, leadin g to the conclusion that starches with higher amylose contents generally co ntain amylopectin with a lower level of branching. The three amylopectin ty pes are referred to as amylopectin I, II and III, with the higher numeral c oinciding with higher branching (alpha-1,4)/(alpha-1,6) ratio, or less bran ching.