Rheological study and a phase diagram on mixture of corn starch and konjac glucomannan

Abstract

This chapter demonstrates how storage (G′) and loss (G″) shear moduli are measured for mixtures of corn starch (CS) and konjac glucomannan (KM) (total polysaccharide concentration—3.50 wt%, CS / KM ratios: 10/0, 9/1, 8/2, 7/3, 6/4). The viscoelastic behavior of aqueous dispersions of CS (2.10–3.50 wt%, 3.50 wt%=10/0) is an intermediate between a weak gel and an elastic gel, and aqueous dispersions of KM (0.35–1.40 wt%) shows a behavior similar to a concentrated polymer solution. The behavior of dispersions of CS and KM mixtures is an intermediate between a concentrated polymer solution and a weak gel. Storage modulus of a CS/KM mixture (constant KM content) as a function of the added CS shows a maximum at a certain CS content. These results suggest that phase separation of the two polymers occur. This is confirmed by confocal laser scanning microscopy. The microstructure of these mixtures is found to be CS continuous under most conditions. This is explained as a consequence of the starch forming a weak gel even when the KM phase volume appears to dominate the microstructure. Under the conditions of this study the KM behaves as a concentrated polymer solution which is trapped by weak gels of CS. The chapter describes the addition of hydrocoUoid to starch is known to increase the viscosity of starch and influence the gelatinization and retrogradation of starch.