Rheological and microstructural characteristics of rice starch-tara gum mixtures

Abstract

Effects of tara gum (TG) at different TG concentrations (0.2-0.6% w/w) on the rheological and pasting properties of rice starch (RS) pastes (5% w/w) were studied. Confocal laser scanning microscopy (CLSM) observation was also conducted to investigate the possible interaction between RS and TG. All RS-TG mixture pastes exhibited a pseudoplastic shear-thinning characteristic (n = 0.17-0.26). RS alone displayed a highly thixotropic behaviour as compared to RS-TG mixtures, showing that the thixotropic loop area markedly decreased in the presence of TG. Consistency index (K), apparent viscosity (eta(a, 100)), storage moduli (G'), and loss moduli (G '') values increased with increasing TG concentration. Viscous characteristics in the RS-TG mixture system were more pronounced compared to the control (0% TG) as evidenced by their higher tan delta values. Rapid visco-analysis showed that the addition of TG resulted in a significant increase in the peak, breakdown, final, and setback viscosities, and their viscosities also increased with an increase in TG concentration. These results suggested that the synergistic effect of TG addition on rheological and pasting properties of RS pastes appeared to be due to phase separation process that occurred as a result of incompatibility between TG and amylose component in starch, as confirmed by CLSM micrographs.