Steady and dynamic shear rheological properties of starch and decolorized Hsian-Tsao leaf gum composite systems

Rapid Visco Analyser (RVA) and dynamic rheological measurements were performed on a mixture of decolorized hsian-tsao leaf gum (dHG) and starch as a function of starch-to-gum ratio (S/G 0:6, 1:5, 2:4, 3:3, 4:2, 5:1, and 6:0), starch type (wheat, corn, and tapioca), and total solid content (2, 3, and 4%). Under S/G of 5:1, 4:2 and 3:3, dHG interacted with starch synergistically, which resulted in a marked increase in viscosity during cooling. The storage modulus of the resulting mixed gel was higher than the loss modulus, and both moduli were almost frequency-independent throughout the frequency range tested, indicating that the composite gels could be classified theologically as elastic gels. Mixed systems with tapioca starch showed higher pseudo-gel viscosity in the RVA test, but lower storage modulus in the dynamic test than those with wheat or corn starch. Such results implied that tapioca starch contributed a more viscous property but wheat and corn starch contributed a more elastic property to the mixed systems.