Influence of purified konjac glucomannan on the gelatinisation and retrogradation properties of maize and potato starches

The effects of purified konjac glucomannan (PKG) on the gelatinisation and retrogradation properties of different starches was investigated by differential scanning calorimetry (DSC) and α-amylase digestion. It was established that when moisture was progressively restricted in starch–water or starch–konjac polysaccharide–water systems, the conclusion temperature by DSC (Tc) increased progressively with the concentration of PKG in the system. This increase in Tc was directly related to the volume fraction of water (as modelled by the modified Flory–Huggins equation) and was considered to be the result of the hydrocolloid limiting water availability for gelatinisation and swelling. In addition, the PKG was extremely effective at retarding ‘long-term’ retrogradation of starch during low temperature storage (reflected in the enthalpy of dissociation by DSC and amount of starch digested by α-amylase). In this context, the konjac hydrocolloid may (a) act as a physical barrier to prevent amylopectin chain association during storage, (b) restrict enzyme–substrate contact and (c) exert a viscosity effect that affects mobility within the stored system.