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 diffe ring amylose contents were measured by enzymatic debranching, followed by high performance size exclusion chromatography (HPSEC). The molecu lar size of amyloses, estimated by -logK(wav), shows progressive decre ase with the increase in amylose content in maize starches. The gel pe rmeation chromatographs of the corresponding amylopectins, debranched with isoamylase, showed bimodal distributions containing long and shor t chains. The average chain length of amylopectin has a correlation wi th amylose content. The correlation coefficients between amylose conte nt and average chain length, long chain length, weight ratio and the m ole 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 th e lowest amylose molecular size and the longest chains, with a high ra tio 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 iodine-complex method, we conclude that long chains of amylopectin in high amylose starches contribute significant ly to apparent amylose content. Copyright (C) 1997 Elsevier Science Lt d. All rights reserved.