Gradual enzymatic modification of barley and potato amylopectin

New potato and barley starches with no amylose were used in order to explore structural changes in amylopectin due to hydrolysis with α-amylase from Bacillus amyloliquifaciens. The degradation pattern was monitored with size exclusion, with light scattering and viscometry detectors for determination of 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 precipitation technique used. Generally the fractions obtained showed a pattern of both decreasing molecular weight and radius of gyration with increasing enzymatic hydrolysis. Fractions that precipitated with the lowest ethanol concentration had the highest values of both average molecular weight and radius of gyration. The unit chain length distributions of the fractions were analysed and the results showed that the chain length distribution varied with the time of hydrolysis. There was also a decreasing trend in average molecular weight with enzyme degradation time for fractions that precipitated at the same ethanol concentration, indicating that the fractionation was affected by structure and not only by molecular weight. Data from this study could be useful for the production of modified amylopectin molecules that vary in composition and characteristics.