Degradation mechanism of amylopectin under ultrasonic irradiation

Abstract

In this study, amylopectin was ultrasonicated and a significant decrease in Mw was detected with extension of the processing time using high-performance size-exclusion chromatography equipped with refractive index detector and multi-angle laser-light scattering. The degradation mechanism was interpreted by means of chain length distribution characterization and 1H NMR spectrum. The disruption of amylopectin was indicated by a preferential degradation of larger molar mass of amylopectin which generating molecular fragments at about the same size, and degree of the maximum degradation was based on a critical molecular size which equalled to the diffusion layer of the collapsed cavitation bubbles in ultrasonic irradiation. The break points firstly occurred at B3 chains (midpoint scission) and then at B2 chains (midpoint scission) with an increase of A chains contents, which resulted in a much narrower molecular size distribution. Both of the α-1,4- and α-1,6-glycosidic bonds in B3 and B2 chains were disrupted in ultrasonic irradiation. However, α-1,6-glycosidic bonds was more likely to break as the degree of branching of the samples decreased with the extension of processing time.