Effect of konjac glucomannan with different molecular weights on physicochemical properties of corn starch

Four konjac glucomannan (KGM) samples with different molecular weight (Mw) were prepared using high-pressure homogenization. The Mw effects of KGM on the particle size distribution, leached amylose, gelatinization, retrogradation, and rheological properties of corn starch (CS) were then investigated. KGM led to a Mw-dependent reduction in the swelling of starch granules and the leaching of amylose. Differential scanning calorimetry results showed that the incorporation of KGM slightly increased the onset and peak gelatinization temperatures of the CS but did not affect the conclusion gelatinization temperatures. Meanwhile, the ΔH increased significantly with the increase of KGM Mw. In addition, the retrogradation enthalpy and retrogradation ratio of CS were found to be significantly decreased with increasing the Mw of the KGM. This was further confirmed by the changes in the syneresis during analysis of freeze-thaw stability and the relative crystallinity as measured by X-ray diffraction. Flow and dynamic shear measurements revealed that both CS and CS-KGM mixtures are pseudoplastic fluids, and that the pseudoplasticity and viscoelasticity were significantly enhanced with increasing Mw of the KGM. The results demonstrated that the Mw of KGM plays an important part in affecting the physicochemical properties of corn starch.