The effects of amylose content on the molecular size of amylose, and on the distribution of amylopectin chain length in maize starches

The amylose to amylopectin ratios in six maize starch samples of differing amylose contents were measured by enzymatic debranching, followed by high performance size exclusion chromatography (HPSEC). The molecular size of amyloses, estimated by -log K_wav, shows progressive decrease with the increase in amylose content in maize starches. The gel permeation chromatographs of the corresponding amylopectins, debranched with isoamylase, showed bimodal distributions containing long and short chains. The average chain length of amylopectin has a correlation with amylose content. The correlation coefficients between amylose content and average chain length, long chain length, weight ratio and the mole ratio of long and short chain length, were 0.97, 0.92, 0.96, 0.94 respectively. The maize starch with the highest amylose content has the lowest amylose molecular size and the longest chains, with a high ratio of long to short chains in its amylopectin fraction. Comparing the values of amylose content determined by HPSEC of starch or debranched starch with those of the iodinecomplex method, we conclude that long chains of amylopectin in high amylose starches contribute significantly to apparent amylose content.