Gradual enzymatic modification of barley and potato amylopectin

New potato and barley starches with no amylose were used in order to explor e structural changes in amylopectin due to hydrolysis with amylase from Bac illus amyloliquifaciens. The degradation pattern was monitored with size ex clusion, with light scattering and viscometry detectors for determination o f molecular weight and radius of gyration. Fractions with relatively narrow molecular weight distributions at high yields were obtained as a result of the gradual enzymatic degradation and the subsequent sequential ethanol pr ecipitation technique used. Generally the fractions obtained showed a patte rn of both decreasing molecular weight and radius of gyration with increasi ng enzymatic hydrolysis. Fractions that precipitated with the lowest ethano l concentration had the highest values of both average molecular weight and radius of gyration. The unit chain length distributions of the fractions w ere analysed and the results showed that the chain length distribution vari ed with the time of hydrolysis. There was also a decreasing trend in averag e molecular weight with enzyme degradation time for fractions that precipit ated at the same ethanol concentration, indicating that the fractionation w as affected by structure and not only by molecular weight. Data from this s tudy could be useful for the production of modified amylopectin molecules t hat vary in composition and characteristics. (C) 2002 Elsevier Science Ltd. All rights reserved.