Thermodynamic incompatibility between denatured whey protein and konjac glucomannan

The current study investigated the effect of a neutral polysaccharide, konjac glucomannan, on the heat-induced gelation of whey protein isolate (WPI) at pH 7. Oscillatory rheology (1. rad/s; 0.5% strain), differential scanning calorimetry and confocal laser scanning microscopy were used to investigate the effect of addition of konjac in the range 0-0.5%. w/w, on the thermal gelation properties of WPI. The minimum gelling concentration for WPI samples was 11%. w/w; the concentration was therefore held constant at this value. Gelation of WPI was induced by heating the samples from 20 to 80°C, holding at 80°C for 30. min, cooling to 20°C, and holding at 20°C for a further 30. min. On incorporation of increasing concentrations of konjac the gelation time decreased, while the storage modulus (G') of the mixed gel systems increased to ~1450. Pa for 11%. w/w WPI containing 0.5%. w/w konjac gels, compared to 15. Pa for 11%. w/w WPI gels (no konjac). This increase in gel strength was attributed to segregative interactions between denatured whey proteins and konjac glucomannan.