Effects of konjac-glucomannan on the gelatinization and retrogradation of corn starch as determined by rheology and differential scanning calorimetry

Effects of konjac-glucomannan (KM) on retrogradation and gelatinization of corn starch (CS) were studied as a function of mixing ratio and of storage time by measuring force-deformation curves, dynamic viscoelasticity, and differential scanning calorimetry(DSC). Total polysaccharide concentration for the rheological experiments was 15 wt % and CS/KM ratios were 15/0, 14.25/0.75, 13.50/ 1.50, and 12.75/2.25. A mixed gel with a CS/KM ratio of 13.50/1.50 showed a larger breaking strain and Young's modulus than a gel of CS plus water (15/0) stored for 1 day. Mixed gels of CS and KM stored for 14 days showed a smaller breaking stress than a gel of CS plus water. The DSC endothermic peak accompanying the gelatinization shifted slightly to higher temperatures with increasing KM concentration. A CS-KM-water mixture (total polysaccharide concentration, 33 wt %) retrograded faster than CS plus water during short storage. Enthalpies of CS-KM-water mixtures stored for 14 days were smaller than that of CS plus water. From the rheological and DSC changes it is suggested that KM promoted CS retrogradation during short-term storage and then retarded it slightly during longer storage times.