Effects of konjac glucomannan on pasting and rheological properties of corn starch

Blend of starch and hydrocolloids is a secure and feasible physical modifying method for native starch. Konjac glucomannan (KGM), a kind of non-ionic hydrocolloids, has been widely used as food additive due to its water holding, thickening and gelling capacity. In this study, the effect of Konjac glucomannan (KGM) on the pasting and rheological properties of corn starch (CS) was investigated. The particle size distribution and low field-nuclear magnetic resonance (LF-NMR) tests were also conducted to further explore the interaction between KGM and corn starch. Rapid visco analysis (RVA) showed that pasting temperature of CS increased with the increase of KGM concentration. KGM addition raised the peak viscosity, breakdown and setback value as well. Dynamic viscoelasticity measurements showed that the storage modulus (G′) and the loss modulus (G″) increased in the presence of KGM, suggesting that KGM could effectively improve the viscoelasticity of CS. The steady shear results showed that the CS-KGM mixtures presented non-Newtonian shear-thinning behavior. The flow behavior index (n) ranged from 0.3479 to 0.2545 as the concentration of KGM increased, indicating that the pseudoplasticity was enhanced with the increasing addition of KGM. In addition, particle size distribution confirmed that KGM inhibited the pasting of corn starch. The low-field nuclear magnetic resonance (LF-NMR) experiment supported the hypothesis that KGM could compete with corn starch for water molecule. The results indicate that KGM significantly changes the pasting, rheological properties of corn starch due to strong interaction between CS and KGM in the composite system.