Pasting and rheological properties of waxy corn starch as affected by guar gum and xanthan gum

Effects of guar (GG) and xanthan (XG) gums (0.35-1.0% w/w) on pasting and rheological properties of waxy corn starch (WCS) (6.0% w/w) were studied. GG had a higher molecular weight but lower intrinsic viscosity than did XG, indicating that the GG chain was more flexible. RVA results indicated that viscosity and pasting temperature of the WCS dispersion during pasting increased with increasing GG or XG concentration. Dynamic viscoelasticity measurements indicated that the WCS/XG mixed pastes exhibited slightly superior viscoelastic properties to the WCS/GG pastes as evidenced by their higher G' and lower tan delta values. Flow tests showed that the WCS/GG pastes exhibited mainly thixotropic hysteresis loops during a full shear cycle, whereas the WCS/XG pastes showed much less thixotropic and eventually became antithixotropic at high XG concentrations. In-shear structural recovery of the pastes increased more with increasing XG concentrations than did pastes with increasing GG concentrations. The differences in molecular characteristics of the GG and XG chains are hypothesized to be responsible for the above mentioned effects. (c) 2007 Elsevier Ltd. All rights reserved.