Heat-induced gels of soy protein and κ-carrageenan at different pH values

P>Heat-induced (90 degrees C/30 min) gelling of soy protein isolate (SPI) and kappa-carrageenan (kappa-CR) systems at pH values of 6.7 and 5.7 was evaluated. kappa-CR addition, increase in protein concentration and reduction in pH led to decreases in the initial gel structure forming temperature. Self-supporting gels were not formed at concentrations of 8% (w/w) SPI or at concentrations below 0.3% (w/w) kappa-CR, but an increase in the concentration of SPI and kappa-CR led to an increase in the stress at rupture without influencing the deformability. Gel properties were a consequence of a simultaneous process of gelling and phase separation during heating. The non-linear parameter of the Blatz, Sharda and Tschoegl (BST) rheological model allowed for the evaluation of the structural characteristics that in general corresponded to strain hardening behaviour. Strain weakening behaviour was observed at high biopolymer concentrations and at pH 6.7, which was associated with accentuated phase separation and a more discontinuous gel network.