Influence of tamarind seed xyloglucan on rheological properties and thermal stability of tapioca starch

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.