Effects of xyloglucan (XG) on rheological properties and thermal stability of tapioca starch (TS) were investigated. Mechanical spectra of 5% w/w TS/XG mixtures changed from gel behavior to concentrated solution and showed higher loss tangent (G ''/G ') with increasing XG concentration. Rapid visco-analysis profiles of 5% TS/XG mixtures at different mixing ratios revealed that peak and final viscosities increased with increasing XG content. From steady shear measurements at 25 degrees C, viscosities of gelatinized TS/ XG mixtures were higher than those of TS pastes, while flow curves of both TS and TS/XG pastes showed shear thinning behavior. Apparent viscosities at 50 s(-1) of TS and TS/XG pastes decreased with increasing temperature but the activation energy of TS/XG mixtures was lower than that of TS alone according to the Arrhenius plot. indicating improved heat stability of TS. Water separation of TS/XG pastes was also lower compared with that of TS alone from freeze-thaw cycle experiments. The results suggest that XG imparted more viscous, liquid-like rheological properties and heat stability to the gelatinized TS/XG mixtures. (c) 2005 Elsevier Ltd. All rights reserved.