Rheology of different hydrocolloids-rice starch blends. Effect of successive heating-cooling cycles

Hydrocolloids are frequently used for modifying starch functionality. In the present study the possible interaction of three different hydrocolloids - guar gum, hydroxypropylmethylcellulose (HPMC) and xanthan gum - with rice starch was explored by determining the pasting, viscoelastic and swelling properties of the rice starch-hydrocolloids mixtures. The impact of successive heating-cooling cycles on the pasting, viscoelasticity and swelling was also determined. Hydrocolloids tested in the range 0.2-0.8% (w/w) significantly modified the pasting, viscoelastic and swelling properties of rice starch-hydrocolloid pastes (8%, w/w) and the extent of the effect was dependent on hydrocolloid concentration. Guar and xanthan gum mixtures with rice starch had the greatest effect on the pasting properties, whereas HPMC mixtures only changed the viscosity during cooling. The starch-hydrocolloids pastes formed weaker gels compared to those of the starch alone. Rheological results suggested the formation of composite network structures with high frequency dependence. Successive multiple-heating cycles allowed the gel to rearrange resulting in altered gel viscoelasticity and release of water soluble compounds that favour phase separation at the highest hydrocolloid level tested.