Rheological properties of starch and whey protein isolate gels

The paste viscosity of starches Amioca (similar to 0.5% amylose), native corn (similar to 27% amylose), Hylon VII (similar to 70% amylose), tapioca (similar to 19% amylose), and their whey protein isolate (WPI; 50/50) mixtures at varying solid concentration of 2.5, 5,10,15 and 20% were determined. At higher gel concentration (20%) during the cooling cycle, WPI paste measured by rapid visco-analyser (RVA) showed a tremendous increase in viscosity over that of the micro visco-amylograph (MVA), 5784 and 184 cP, respectively. RVA gels had a more uniform network of coarse particles (similar to 250-500 nm) than the fine structures (similar to 50 nm) in those of the MVA. Inclusion of WPI reduced the paste viscosity of all starches by at least 50%, except for Hylon VII at 20% solid concentration. ne strength of Hylon VII and corn starch gels was reduced by WPI. In contrast, gels of WPI/tapioca (G' = 45.4 Pa) and WPI/amioca (G' = 18.3 Pa) had similar rheological properties as their pure starch control (G' = 47.4 Pa and G' = 15.3 Pa for Tapioca and Amioca, respectively).