Molecular characteristics of barley starches with variable amylose content

The granular and molecular characteristics of four types of hulless barley starches (normal, high amylose, waxy and zero amylose) were investigated by particle size analysis and size exclusion chromatography (SEC) with light scattering detection. Although bimodal size distribution of granules was observed for normal, waxy and zero amylose starches, the proportion of large to small granules for each type of starch differed substantially. The granular size distribution of high amylose starches was unimodal, showing the highest proportion of small granule (3 μm). For the intact starch molecules, molecular weights of high (amylopectin) and low (amylose) Mw fractions were in the range from 136×106 to 305×106 and from 2.73×106 to 5.67×106, respectively. The lowest Mw values were observed for amylopectin in high amylose starches. A good correlation (r2=0.96) between Mw and Rg of all amylopectins was found. After debranching of starch samples, significantly lower Mw values were observed for amylose, indicating the existence of branches in amylose molecules. Debranched amylopectins exhibited trimodal distributions of long B, intermediate B and short B+A chains. The longest amylopectin branches were found in high amylose barley starches.