Inhibition of amylopectin retrogradation by partial beta-amylolysis

The rate of retrogradation of amylopectin solution differs from one starch variety to another and it is thought to be due to the different length of the external chains of amylopectin. A shortening of the external chains of waxy maize and potato amylopectin was performed with beta-amylase. Partial beta-amylolysis produced a significant fraction of chains having 2-6 glucose units. A high linear correlation (R > 0.97) was found between the enthalpy of retrograded amylopectin measured by DSC, or percent solid measured by low frequency pulsed NMR, and average external chain length. No retrogradation appeared to occur when the external chains of both amylopectins had 11 or less glucose units on average. The inhibition of retrogradation appears to be caused primarily by the presence of very short external chains, which hinders the reassociation of the long external chains.