Effect of heating temperature, pH, concentration and starch/whey protein ratio on the viscoelastic properties of corn starch/whey protein mixed gels

The viscoelastic properties of corn starch (CS) gels were more dependent on heating temperature, while the properties of whey protein isolate (WPI) ge ls were more dependent on pH. Thus heating temperature (75, 55, 95 degreesC ) and pH (5, 7, 9) were varied to obtain a series of mixed gels with intere sting viscoelastic properties. WPI gels showed extensive stress relaxation (SR) indicative of a highly transient network structure, while GS gels rela xed very little in 2000 s. Base on SR results, it appeared that CS/WPI mixe d gels with 25 and 50% CS formed compatible network structures at 15% total solids only at pH 9. This supposition was supported by SEM microstructures obtained for dehydrated gels and a synergistic increase in the large-strai n fracture stress for these gels. Some synergy was also found for mixed gel s at 30% total solids at pH 9, while at pH 7 the mixed gels seemed to conta in separate additive WPI and CS networks unlike the case for pH 7 at 15% to tal solids. In both cases (15 and 30% total solids) the degree of elasticit y of the mixed gels decreased as the WPI content increased. Mixed gels (CS: WPI=0.5) at pH 9 showed increased fracture stress and fracture strain relat ive to the same gels at pH 7. This suggests that a unique chemical compatib ility exists at pH 9 and results in gels that combine the elasticity of CS and the interval stress dissipation of WPI. (C) 2001 Society of Chemical in dustry.